如何正确克隆 JavaScript object？

Question

I have an object x . I'd like to copy it as object y , such that changes to y do not modify x . I realized that copying objects derived from built-in JavaScript objects will result in extra, unwanted properties. This isn't a problem, since I'm copying one of my own literal-constructed objects.

How do I correctly clone a JavaScript object?

Answer 1

2022 update

There's a new JS standard called structured cloning . It works on all browsers:

const clone = structuredClone(object);

Old answer

To do this for any object in JavaScript will not be simple or straightforward. You will run into the problem of erroneously picking up attributes from the object's prototype that should be left in the prototype and not copied to the new instance. If, for instance, you are adding a clone method to Object.prototype , as some answers depict, you will need to explicitly skip that attribute. But what if there are other additional methods added to Object.prototype , or other intermediate prototypes, that you don't know about? In that case, you will copy attributes you shouldn't, so you need to detect unforeseen, non-local attributes with the hasOwnProperty method.

In addition to non-enumerable attributes, you'll encounter a tougher problem when you try to copy objects that have hidden properties. For example, prototype is a hidden property of a function. Also, an object's prototype is referenced with the attribute __proto__ , which is also hidden, and will not be copied by a for/in loop iterating over the source object's attributes. I think __proto__ might be specific to Firefox's JavaScript interpreter and it may be something different in other browsers, but you get the picture. Not everything is enumerable. You can copy a hidden attribute if you know its name, but I don't know of any way to discover it automatically.

Yet another snag in the quest for an elegant solution is the problem of setting up the prototype inheritance correctly. If your source object's prototype is Object , then simply creating a new general object with {} will work, but if the source's prototype is some descendant of Object , then you are going to be missing the additional members from that prototype which you skipped using the hasOwnProperty filter, or which were in the prototype, but weren't enumerable in the first place. One solution might be to call the source object's constructor property to get the initial copy object and then copy over the attributes, but then you still will not get non-enumerable attributes. For example, a Date object stores its data as a hidden member:

function clone(obj) {
    if (null == obj || "object" != typeof obj) return obj;
    var copy = obj.constructor();
    for (var attr in obj) {
        if (obj.hasOwnProperty(attr)) copy[attr] = obj[attr];
    }
    return copy;
}

var d1 = new Date();

/* Executes function after 5 seconds. */
setTimeout(function(){
    var d2 = clone(d1);
    alert("d1 = " + d1.toString() + "\nd2 = " + d2.toString());
}, 5000);

The date string for d1 will be 5 seconds behind that of d2 . A way to make one Date the same as another is by calling the setTime method, but that is specific to the Date class. I don't think there is a bullet-proof general solution to this problem, though I would be happy to be wrong!

When I had to implement general deep copying I ended up compromising by assuming that I would only need to copy a plain Object , Array , Date , String , Number , or Boolean . The last 3 types are immutable, so I could perform a shallow copy and not worry about it changing. I further assumed that any elements contained in Object or Array would also be one of the 6 simple types in that list. This can be accomplished with code like the following:

function clone(obj) {
    var copy;

    // Handle the 3 simple types, and null or undefined
    if (null == obj || "object" != typeof obj) return obj;

    // Handle Date
    if (obj instanceof Date) {
        copy = new Date();
        copy.setTime(obj.getTime());
        return copy;
    }

    // Handle Array
    if (obj instanceof Array) {
        copy = [];
        for (var i = 0, len = obj.length; i < len; i++) {
            copy[i] = clone(obj[i]);
        }
        return copy;
    }

    // Handle Object
    if (obj instanceof Object) {
        copy = {};
        for (var attr in obj) {
            if (obj.hasOwnProperty(attr)) copy[attr] = clone(obj[attr]);
        }
        return copy;
    }

    throw new Error("Unable to copy obj! Its type isn't supported.");
}

The above function will work adequately for the 6 simple types I mentioned, as long as the data in the objects and arrays form a tree structure. That is, there isn't more than one reference to the same data in the object. For example:

// This would be cloneable:
var tree = {
    "left"  : { "left" : null, "right" : null, "data" : 3 },
    "right" : null,
    "data"  : 8
};

// This would kind-of work, but you would get 2 copies of the 
// inner node instead of 2 references to the same copy
var directedAcylicGraph = {
    "left"  : { "left" : null, "right" : null, "data" : 3 },
    "data"  : 8
};
directedAcyclicGraph["right"] = directedAcyclicGraph["left"];

// Cloning this would cause a stack overflow due to infinite recursion:
var cyclicGraph = {
    "left"  : { "left" : null, "right" : null, "data" : 3 },
    "data"  : 8
};
cyclicGraph["right"] = cyclicGraph;

It will not be able to handle any JavaScript object, but it may be sufficient for many purposes as long as you don't assume that it will just work for anything you throw at it.

Answer 2

If you do not use Date s, functions, undefined, regExp or Infinity within your object, a very simple one liner is JSON.parse(JSON.stringify(object)) :

 const a = { string: 'string', number: 123, bool: false, nul: null, date: new Date(), // stringified undef: undefined, // lost inf: Infinity, // forced to 'null' } console.log(a); console.log(typeof a.date); // Date object const clone = JSON.parse(JSON.stringify(a)); console.log(clone); console.log(typeof clone.date); // result of .toISOString()

This works for all kind of objects containing objects, arrays, strings, booleans and numbers.

See also this article about the structured clone algorithm of browsers which is used when posting messages to and from a worker. It also contains a function for deep cloning.

Answer 3

With jQuery, you can shallow copy with extend :

var copiedObject = jQuery.extend({}, originalObject)

subsequent changes to the copiedObject will not affect the originalObject , and vice versa.

Or to make a deep copy :

var copiedObject = jQuery.extend(true, {}, originalObject)

Answer 4

In ECMAScript 6 there is Object.assign method, which copies values of all enumerable own properties from one object to another. For example:

var x = {myProp: "value"};
var y = Object.assign({}, x); 

But be aware this is a shallow copy - nested objects are still copied as reference.

Answer 5

Per MDN :

• If you want shallow copy, use Object.assign({}, a)
• For "deep" copy, use JSON.parse(JSON.stringify(a))

There is no need for external libraries but you need to check browser compatibility first .

Answer 6

An elegant way to clone a Javascript object in one line of code

An Object.assign method is part of the ECMAScript 2015 (ES6) standard and does exactly what you need.

var clone = Object.assign({}, obj);

The Object.assign() method is used to copy the values of all enumerable own properties from one or more source objects to a target object.

Read more...

The polyfill to support older browsers:

if (!Object.assign) {
  Object.defineProperty(Object, 'assign', {
    enumerable: false,
    configurable: true,
    writable: true,
    value: function(target) {
      'use strict';
      if (target === undefined || target === null) {
        throw new TypeError('Cannot convert first argument to object');
      }

      var to = Object(target);
      for (var i = 1; i < arguments.length; i++) {
        var nextSource = arguments[i];
        if (nextSource === undefined || nextSource === null) {
          continue;
        }
        nextSource = Object(nextSource);

        var keysArray = Object.keys(nextSource);
        for (var nextIndex = 0, len = keysArray.length; nextIndex < len; nextIndex++) {
          var nextKey = keysArray[nextIndex];
          var desc = Object.getOwnPropertyDescriptor(nextSource, nextKey);
          if (desc !== undefined && desc.enumerable) {
            to[nextKey] = nextSource[nextKey];
          }
        }
      }
      return to;
    }
  });
}

Answer 7

There are many answers, but none that mentions Object.create from ECMAScript 5, which admittedly does not give you an exact copy, but sets the source as the prototype of the new object.

Thus, this is not an exact answer to the question, but it is a one-line solution and thus elegant. And it works best for 2 cases:

1. Where such inheritance is useful (duh!)
2. Where the source object won't be modified, thus making the relation between the 2 objects a non issue.

Example:

var foo = { a : 1 };
var bar = Object.create(foo);
foo.a; // 1
bar.a; // 1
foo.a = 2;
bar.a; // 2 - prototype changed
bar.a = 3;
foo.a; // Still 2, since setting bar.a makes it an "own" property

Why do I consider this solution to be superior? It's native, thus no looping, no recursion. However, older browsers will need a polyfill.

Answer 8

There are several issues with most solutions on the internet. So I decided to make a follow-up, which includes, why the accepted answer shouldn't be accepted.

starting situation

I want to deep-copy a Javascript Object with all of its children and their children and so on. But since I'm not kind of a normal developer, my Object has normal properties , circular structures and even nested objects .

So let's create a circular structure and a nested object first.

function Circ() {
    this.me = this;
}

function Nested(y) {
    this.y = y;
}

Let's bring everything together in an Object named a .

var a = {
    x: 'a',
    circ: new Circ(),
    nested: new Nested('a')
};

Next, we want to copy a into a variable named b and mutate it.

var b = a;

b.x = 'b';
b.nested.y = 'b';

You know what happened here because if not you wouldn't even land on this great question.

console.log(a, b);

a --> Object {
    x: "b",
    circ: Circ {
        me: Circ { ... }
    },
    nested: Nested {
        y: "b"
    }
}

b --> Object {
    x: "b",
    circ: Circ {
        me: Circ { ... }
    },
    nested: Nested {
        y: "b"
    }
}

Now let's find a solution.

JSON

The first attempt I tried was using JSON .

var b = JSON.parse( JSON.stringify( a ) );

b.x = 'b';
b.nested.y = 'b';

Don't waste too much time on it, you'll get TypeError: Converting circular structure to JSON .

Recursive copy (the accepted "answer")

Let's have a look at the accepted answer.

function cloneSO(obj) {
    // Handle the 3 simple types, and null or undefined
    if (null == obj || "object" != typeof obj) return obj;

    // Handle Date
    if (obj instanceof Date) {
        var copy = new Date();
        copy.setTime(obj.getTime());
        return copy;
    }

    // Handle Array
    if (obj instanceof Array) {
        var copy = [];
        for (var i = 0, len = obj.length; i < len; i++) {
            copy[i] = cloneSO(obj[i]);
        }
        return copy;
    }

    // Handle Object
    if (obj instanceof Object) {
        var copy = {};
        for (var attr in obj) {
            if (obj.hasOwnProperty(attr)) copy[attr] = cloneSO(obj[attr]);
        }
        return copy;
    }

    throw new Error("Unable to copy obj! Its type isn't supported.");
}

Looks good, heh? It's a recursive copy of the object and handles other types as well, like Date , but that wasn't a requirement.

var b = cloneSO(a);

b.x = 'b';
b.nested.y = 'b';

Recursion and circular structures doesn't work well together... RangeError: Maximum call stack size exceeded

native solution

After arguing with my co-worker, my boss asked us what happened, and he found a simple solution after some googling. It's called Object.create .

var b = Object.create(a);

b.x = 'b';
b.nested.y = 'b';

This solution was added to Javascript some time ago and even handles circular structure .

console.log(a, b);

a --> Object {
    x: "a",
    circ: Circ {
        me: Circ { ... }
    },
    nested: Nested {
        y: "b"
    }
}

b --> Object {
    x: "b",
    circ: Circ {
        me: Circ { ... }
    },
    nested: Nested {
        y: "b"
    }
}

... and you see, it didn't work with the nested structure inside.

polyfill for the native solution

There's a polyfill for Object.create in the older browser just like the IE 8. It's something like recommended by Mozilla, and of course, it's not perfect and results in the same problem as the native solution .

function F() {};
function clonePF(o) {
    F.prototype = o;
    return new F();
}

var b = clonePF(a);

b.x = 'b';
b.nested.y = 'b';

I've put F outside the scope so we can have a look at what instanceof tells us.

console.log(a, b);

a --> Object {
    x: "a",
    circ: Circ {
        me: Circ { ... }
    },
    nested: Nested {
        y: "b"
    }
}

b --> F {
    x: "b",
    circ: Circ {
        me: Circ { ... }
    },
    nested: Nested {
        y: "b"
    }
}

console.log(typeof a, typeof b);

a --> object
b --> object

console.log(a instanceof Object, b instanceof Object);

a --> true
b --> true

console.log(a instanceof F, b instanceof F);

a --> false
b --> true

Same problem as the native solution , but a little bit worse output.

the better (but not perfect) solution

When digging around, I found a similar question ( In Javascript, when performing a deep copy, how do I avoid a cycle, due to a property being "this"? ) to this one, but with a way better solution.

function cloneDR(o) {
    const gdcc = "__getDeepCircularCopy__";
    if (o !== Object(o)) {
        return o; // primitive value
    }

    var set = gdcc in o,
        cache = o[gdcc],
        result;
    if (set && typeof cache == "function") {
        return cache();
    }
    // else
    o[gdcc] = function() { return result; }; // overwrite
    if (o instanceof Array) {
        result = [];
        for (var i=0; i<o.length; i++) {
            result[i] = cloneDR(o[i]);
        }
    } else {
        result = {};
        for (var prop in o)
            if (prop != gdcc)
                result[prop] = cloneDR(o[prop]);
            else if (set)
                result[prop] = cloneDR(cache);
    }
    if (set) {
        o[gdcc] = cache; // reset
    } else {
        delete o[gdcc]; // unset again
    }
    return result;
}

var b = cloneDR(a);

b.x = 'b';
b.nested.y = 'b';

And let's have a look at the output...

console.log(a, b);

a --> Object {
    x: "a",
    circ: Object {
        me: Object { ... }
    },
    nested: Object {
        y: "a"
    }
}

b --> Object {
    x: "b",
    circ: Object {
        me: Object { ... }
    },
    nested: Object {
        y: "b"
    }
}

console.log(typeof a, typeof b);

a --> object
b --> object

console.log(a instanceof Object, b instanceof Object);

a --> true
b --> true

console.log(a instanceof F, b instanceof F);

a --> false
b --> false

The requirements are matched, but there are still some smaller issues, including changing the instance of nested and circ to Object .

The structure of trees that share a leaf won't be copied, they will become two independent leaves:

        [Object]                     [Object]
         /    \                       /    \
        /      \                     /      \
      |/_      _\|                 |/_      _\|  
  [Object]    [Object]   ===>  [Object]    [Object]
       \        /                 |           |
        \      /                  |           |
        _\|  |/_                 \|/         \|/
        [Object]               [Object]    [Object]

conclusion

The last solution using recursion and a cache, may not be the best, but it's a real deep-copy of the object. It handles simple properties , circular structures and nested object , but it will mess up the instance of them while cloning.

jsfiddle

Answer 9

If you're okay with a shallow copy, the underscore.js library has a clone method.

y = _.clone(x);

or you can extend it like

copiedObject = _.extend({},originalObject);

Answer 10

OK, imagine you have this object below and you want to clone it:

let obj = {a:1, b:2, c:3}; //ES6

or

var obj = {a:1, b:2, c:3}; //ES5

the answer is mainly depeneds on which ECMAscript you using, in ES6+ , you can simply use Object.assign to do the clone:

let cloned = Object.assign({}, obj); //new {a:1, b:2, c:3};

or using spread operator like this:

let cloned = {...obj}; //new {a:1, b:2, c:3};

But if you using ES5 , you can use few methods, but the JSON.stringify , just make sure you not using for a big chunk of data to copy, but it could be one line handy way in many cases, something like this:

let cloned = JSON.parse(JSON.stringify(obj)); 
//new {a:1, b:2, c:3};, can be handy, but avoid using on big chunk of data over and over

Answer 11

Update 06 July 2020

There are three (3) ways to clone objects in JavaScript. As objects in JavaScript are reference values, you can't simply just copy using the =.

The ways are:

const food = { food: 'apple', drink: 'milk' }


// 1. Using the "Spread"
// ------------------

{ ...food }


// 2. Using "Object.assign"
// ------------------

Object.assign({}, food)


// 3. "JSON"
// ------------------

JSON.parse(JSON.stringify(food))

// RESULT:
// { food: 'apple', drink: 'milk' }

This can be used as a reference summary.

Answer 12

One particularly inelegant solution is to use JSON encoding to make deep copies of objects that do not have member methods. The methodology is to JSON encode your target object, then by decoding it, you get the copy you are looking for. You can decode as many times as you want to make as many copies as you need.

Of course, functions do not belong in JSON, so this only works for objects without member methods.

This methodology was perfect for my use case, since I'm storing JSON blobs in a key-value store, and when they are exposed as objects in a JavaScript API, each object actually contains a copy of the original state of the object so we can calculate the delta after the caller has mutated the exposed object.

var object1 = {key:"value"};
var object2 = object1;

object2 = JSON.stringify(object1);
object2 = JSON.parse(object2);

object2.key = "a change";
console.log(object1);// returns value

Answer 13

You can simply use a spread property to copy an object without references. But be careful (see comments), the 'copy' is just on the lowest object/array level. Nested properties are still references!

---

Complete clone:

let x = {a: 'value1'}
let x2 = {...x}

// => mutate without references:

x2.a = 'value2'
console.log(x.a)    // => 'value1'

Clone with references on second level:

const y = {a: {b: 'value3'}}
const y2 = {...y}

// => nested object is still a references:

y2.a.b = 'value4'
console.log(y.a.b)    // => 'value4'

---

JavaScript actually does not support deep clones natively. Use an utility function. For example Ramda:

http://ramdajs.com/docs/#clone

Answer 14

const objClone = { ...obj };

请注意，嵌套对象仍被复制为引用。

Answer 15

From this article: How to copy arrays and objects in Javascript by Brian Huisman:

Object.prototype.clone = function() {
  var newObj = (this instanceof Array) ? [] : {};
  for (var i in this) {
    if (i == 'clone') continue;
    if (this[i] && typeof this[i] == "object") {
      newObj[i] = this[i].clone();
    } else newObj[i] = this[i]
  } return newObj;
};

Answer 16

For those using AngularJS, there is also direct method for cloning or extending of the objects in this library.

var destination = angular.copy(source);

or

angular.copy(source, destination);

More in angular.copy documentation ...

Answer 17

function clone(obj) {
    if(obj == null || typeof(obj) != 'object')
        return obj;    
    var temp = new obj.constructor(); 
    for(var key in obj)
        temp[key] = clone(obj[key]);    
    return temp;
}

Answer 18

A.Levy's answer is almost complete, here is my little contribution: there is a way how to handle recursive references , see this line

if(this[attr]==this) copy[attr] = copy;

If the object is XML DOM element, we must use cloneNode instead

if(this.cloneNode) return this.cloneNode(true);

Inspired by A.Levy's exhaustive study and Calvin's prototyping approach, I offer this solution:

Object.prototype.clone = function() {
  if(this.cloneNode) return this.cloneNode(true);
  var copy = this instanceof Array ? [] : {};
  for(var attr in this) {
    if(typeof this[attr] == "function" || this[attr]==null || !this[attr].clone)
      copy[attr] = this[attr];
    else if(this[attr]==this) copy[attr] = copy;
    else copy[attr] = this[attr].clone();
  }
  return copy;
}

Date.prototype.clone = function() {
  var copy = new Date();
  copy.setTime(this.getTime());
  return copy;
}

Number.prototype.clone = 
Boolean.prototype.clone =
String.prototype.clone = function() {
  return this;
}

See also Andy Burke's note in the answers.

Answer 19

Performance

Today 2020.04.30 I perform tests of chosen solutions on Chrome v81.0, Safari v13.1 and Firefox v75.0 on MacOs High Sierra v10.13.6.

I focus on speed of copy DATA (object with simple type fields, not methods etc.). The solutions AI can make only shallow copy, solutions JU can make deep copy.

Results for shallow copy

• solution {...obj} (A) is fastest on chrome and firefox and medium fast on safari
• solution based on Object.assign (B) is fast on all browsers
• jQuery (E) and lodash (F,G,H) solutions are medium/quite fast
• solution JSON.parse/stringify (K) is quite slow
• solutions D and U are slow on all browsers

Results for deep copy

• solution Q is fastest on all browsers
• jQuery (L) and lodash (J) are medium fast
• solution JSON.parse/stringify (K) is quite slow
• solution U is slowest on all browsers
• lodash (J) and solution U crash on Chrome for 1000 level deep object

Details

For choosen solutions: A B C(my) D E F G H I J K L M N O P Q R S T U , I perform 4 tests

• shallow-small: object with 10 non-nested fields - you can run it HERE
• shallow-big: object with 1000 non-nested fields - you can run it HERE
• deep-small: object with 10 levels-nested fields - you can run it HERE
• deep-big: object with 1000 levels-nested fields - you can run it HERE

Objects used in tests are show in below snippet

 let obj_ShallowSmall = { field0: false, field1: true, field2: 1, field3: 0, field4: null, field5: [], field6: {}, field7: "text7", field8: "text8", } let obj_DeepSmall = { level0: { level1: { level2: { level3: { level4: { level5: { level6: { level7: { level8: { level9: [[[[[[[[[['abc']]]]]]]]]], }}}}}}}}}, }; let obj_ShallowBig = Array(1000).fill(0).reduce((a,c,i) => (a['field'+i]=getField(i),a) ,{}); let obj_DeepBig = genDeepObject(1000); // ------------------ // Show objects // ------------------ console.log('obj_ShallowSmall:',JSON.stringify(obj_ShallowSmall)); console.log('obj_DeepSmall:',JSON.stringify(obj_DeepSmall)); console.log('obj_ShallowBig:',JSON.stringify(obj_ShallowBig)); console.log('obj_DeepBig:',JSON.stringify(obj_DeepBig)); // ------------------ // HELPERS // ------------------ function getField(k) { let i=k%10; if(i==0) return false; if(i==1) return true; if(i==2) return k; if(i==3) return 0; if(i==4) return null; if(i==5) return []; if(i==6) return {}; if(i>=7) return "text"+k; } function genDeepObject(N) { // generate: {level0:{level1:{...levelN: {end:[[[...N-times...['abc']...]]] }}}...}}} let obj={}; let o=obj; let arr = []; let a=arr; for(let i=0; i<N; i++) { o['level'+i]={}; o=o['level'+i]; let aa=[]; a.push(aa); a=aa; } a[0]='abc'; o['end']=arr; return obj; }

Below snippet presents tested solutions and shows differences between them

 function A(obj) { return {...obj} } function B(obj) { return Object.assign({}, obj); } function C(obj) { return Object.keys(obj).reduce( (a,c) => (a[c]=obj[c], a), {}) } function D(obj) { let copyOfObject = {}; Object.defineProperties(copyOfObject, Object.getOwnPropertyDescriptors(obj)); return copyOfObject; } function E(obj) { return jQuery.extend({}, obj) // shallow } function F(obj) { return _.clone(obj); } function G(obj) { return _.clone(obj,true); } function H(obj) { return _.extend({},obj); } function I(obj) { if (null == obj || "object" != typeof obj) return obj; var copy = obj.constructor(); for (var attr in obj) { if (obj.hasOwnProperty(attr)) copy[attr] = obj[attr]; } return copy; } function J(obj) { return _.cloneDeep(obj,true); } function K(obj) { return JSON.parse(JSON.stringify(obj)); } function L(obj) { return jQuery.extend(true, {}, obj) // deep } function M(obj) { if(obj == null || typeof(obj) != 'object') return obj; var temp = new obj.constructor(); for(var key in obj) temp[key] = M(obj[key]); return temp; } function N(obj) { let EClone = function(obj) { var newObj = (obj instanceof Array) ? [] : {}; for (var i in obj) { if (i == 'EClone') continue; if (obj[i] && typeof obj[i] == "object") { newObj[i] = EClone(obj[i]); } else newObj[i] = obj[i] } return newObj; }; return EClone(obj); }; function O(obj) { if (obj == null || typeof obj != "object") return obj; if (obj.constructor != Object && obj.constructor != Array) return obj; if (obj.constructor == Date || obj.constructor == RegExp || obj.constructor == Function || obj.constructor == String || obj.constructor == Number || obj.constructor == Boolean) return new obj.constructor(obj); let to = new obj.constructor(); for (var name in obj) { to[name] = typeof to[name] == "undefined" ? O(obj[name], null) : to[name]; } return to; } function P(obj) { function clone(target, source){ for(let key in source){ // Use getOwnPropertyDescriptor instead of source[key] to prevent from trigering setter/getter. let descriptor = Object.getOwnPropertyDescriptor(source, key); if(descriptor.value instanceof String){ target[key] = new String(descriptor.value); } else if(descriptor.value instanceof Array){ target[key] = clone([], descriptor.value); } else if(descriptor.value instanceof Object){ let prototype = Reflect.getPrototypeOf(descriptor.value); let cloneObject = clone({}, descriptor.value); Reflect.setPrototypeOf(cloneObject, prototype); target[key] = cloneObject; } else { Object.defineProperty(target, key, descriptor); } } let prototype = Reflect.getPrototypeOf(source); Reflect.setPrototypeOf(target, prototype); return target; } return clone({},obj); } function Q(obj) { var copy; // Handle the 3 simple types, and null or undefined if (null == obj || "object" != typeof obj) return obj; // Handle Date if (obj instanceof Date) { copy = new Date(); copy.setTime(obj.getTime()); return copy; } // Handle Array if (obj instanceof Array) { copy = []; for (var i = 0, len = obj.length; i < len; i++) { copy[i] = Q(obj[i]); } return copy; } // Handle Object if (obj instanceof Object) { copy = {}; for (var attr in obj) { if (obj.hasOwnProperty(attr)) copy[attr] = Q(obj[attr]); } return copy; } throw new Error("Unable to copy obj! Its type isn't supported."); } function R(obj) { const gdcc = "__getDeepCircularCopy__"; if (obj !== Object(obj)) { return obj; // primitive value } var set = gdcc in obj, cache = obj[gdcc], result; if (set && typeof cache == "function") { return cache(); } // else obj[gdcc] = function() { return result; }; // overwrite if (obj instanceof Array) { result = []; for (var i=0; i<obj.length; i++) { result[i] = R(obj[i]); } } else { result = {}; for (var prop in obj) if (prop != gdcc) result[prop] = R(obj[prop]); else if (set) result[prop] = R(cache); } if (set) { obj[gdcc] = cache; // reset } else { delete obj[gdcc]; // unset again } return result; } function S(obj) { const cache = new WeakMap(); // Map of old - new references function copy(object) { if (typeof object !== 'object' || object === null || object instanceof HTMLElement ) return object; // primitive value or HTMLElement if (object instanceof Date) return new Date().setTime(object.getTime()); if (object instanceof RegExp) return new RegExp(object.source, object.flags); if (cache.has(object)) return cache.get(object); const result = object instanceof Array ? [] : {}; cache.set(object, result); // store reference to object before the recursive starts if (object instanceof Array) { for(const o of object) { result.push(copy(o)); } return result; } const keys = Object.keys(object); for (const key of keys) result[key] = copy(object[key]); return result; } return copy(obj); } function T(obj){ var clonedObjectsArray = []; var originalObjectsArray = []; //used to remove the unique ids when finished var next_objid = 0; function objectId(obj) { if (obj == null) return null; if (obj.__obj_id == undefined){ obj.__obj_id = next_objid++; originalObjectsArray[obj.__obj_id] = obj; } return obj.__obj_id; } function cloneRecursive(obj) { if (null == obj || typeof obj == "string" || typeof obj == "number" || typeof obj == "boolean") return obj; // Handle Date if (obj instanceof Date) { var copy = new Date(); copy.setTime(obj.getTime()); return copy; } // Handle Array if (obj instanceof Array) { var copy = []; for (var i = 0; i < obj.length; ++i) { copy[i] = cloneRecursive(obj[i]); } return copy; } // Handle Object if (obj instanceof Object) { if (clonedObjectsArray[objectId(obj)] != undefined) return clonedObjectsArray[objectId(obj)]; var copy; if (obj instanceof Function)//Handle Function copy = function(){return obj.apply(this, arguments);}; else copy = {}; clonedObjectsArray[objectId(obj)] = copy; for (var attr in obj) if (attr != "__obj_id" && obj.hasOwnProperty(attr)) copy[attr] = cloneRecursive(obj[attr]); return copy; } throw new Error("Unable to copy obj! Its type isn't supported."); } var cloneObj = cloneRecursive(obj); //remove the unique ids for (var i = 0; i < originalObjectsArray.length; i++) { delete originalObjectsArray[i].__obj_id; }; return cloneObj; } function U(obj) { /* Deep copy objects by value rather than by reference, exception: `Proxy` */ const seen = new WeakMap() return clone(obj) function defineProp(object, key, descriptor = {}, copyFrom = {}) { const { configurable: _configurable, writable: _writable } = Object.getOwnPropertyDescriptor(object, key) || { configurable: true, writable: true } const test = _configurable // Can redefine property && (_writable === undefined || _writable) // Can assign to property if (!test || arguments.length <= 2) return test const basisDesc = Object.getOwnPropertyDescriptor(copyFrom, key) || { configurable: true, writable: true } // Custom… || {}; // …or left to native default settings ["get", "set", "value", "writable", "enumerable", "configurable"] .forEach(attr => descriptor[attr] === undefined && (descriptor[attr] = basisDesc[attr]) ) const { get, set, value, writable, enumerable, configurable } = descriptor return Object.defineProperty(object, key, { enumerable, configurable, ...get || set ? { get, set } // Accessor descriptor : { value, writable } // Data descriptor }) } function clone(object) { if (object !== Object(object)) return object /* —— Check if the object belongs to a primitive data type */ if (object instanceof Node) return object.cloneNode(true) /* —— Clone DOM trees */ let _object // The clone of object switch (object.constructor) { case Array: case Object: _object = cloneObject(object) break case Date: _object = new Date(+object) break case Function: const fnStr = String(object) _object = new Function("return " + (/^(?!function |[^{]+?=>)[^(]+?\(/.test(fnStr) ? "function " : "" ) + fnStr )() copyPropDescs(_object, object) break case RegExp: _object = new RegExp(object) break default: switch (Object.prototype.toString.call(object.constructor)) { // // Stem from: case "[object Function]": // `class` case "[object Undefined]": // `Object.create(null)` _object = cloneObject(object) break default: // `Proxy` _object = object } } return _object } function cloneObject(object) { if (seen.has(object)) return seen.get(object) /* —— Handle recursive references (circular structures) */ const _object = Array.isArray(object) ? [] : Object.create(Object.getPrototypeOf(object)) /* —— Assign [[Prototype]] for inheritance */ seen.set(object, _object) /* —— Make `_object` the associative mirror of `object` */ Reflect.ownKeys(object).forEach(key => defineProp(_object, key, { value: clone(object[key]) }, object) ) return _object } function copyPropDescs(target, source) { Object.defineProperties(target, Object.getOwnPropertyDescriptors(source) ) } } // ------------------------ // Test properties // ------------------------ console.log(` shallow deep func circ undefined date RegExp bigInt`) log(A); log(B); log(C); log(D); log(E); log(F); log(G); log(H); log(I); log(J); log(K); log(L); log(M); log(N); log(O); log(P); log(Q); log(R); log(S); log(T); log(U); console.log(` shallow deep func circ undefined date RegExp bigInt ---- LEGEND: shallow - solution create shallow copy deep - solution create deep copy func - solution copy functions circ - solution can copy object with circular references undefined - solution copy fields with undefined value date - solution can copy date RegExp - solution can copy fields with regular expressions bigInt - solution can copy BigInt `) // ------------------------ // Helper functions // ------------------------ function deepCompare(obj1,obj2) { return JSON.stringify(obj1)===JSON.stringify(obj2); } function getCase() { // pure data case return { undef: undefined, bool: true, num: 1, str: "txt1", e1: null, e2: [], e3: {}, e4: 0, e5: false, arr: [ false, 2, "txt3", null, [], {}, [ true,4,"txt5",null, [], {}, [true,6,"txt7",null,[],{} ], {bool: true,num: 8, str: "txt9", e1:null, e2:[] ,e3:{} ,e4: 0, e5: false} ], {bool: true,num: 10, str: "txt11", e1:null, e2:[] ,e3:{} ,e4: 0, e5: false} ], obj: { bool: true, num: 12, str: "txt13", e1: null, e2: [], e3: {}, e4: 0, e5: false, arr: [true,14,"txt15",null,[],{} ], obj: { bool: true, num: 16, str: "txt17", e1: null, e2: [], e3: {}, e4: 0, e5: false, arr: [true,18,"txt19",null,[],{} ], obj: {bool: true,num: 20, str: "txt21", e1:null, e2:[] ,e3:{} ,e4: 0, e5: false} } } }; } function check(org, copy, field, newValue) { copy[field] = newValue; return deepCompare(org,copy); } function testFunc(f) { let o = { a:1, fun: (i,j)=> i+j }; let c = f(o); let val = false try{ val = c.fun(3,4)==7; } catch(e) { } return val; } function testCirc(f) { function Circ() { this.me = this; } var o = { x: 'a', circ: new Circ(), obj_circ: null, }; o.obj_circ = o; let val = false; try{ let c = f(o); val = (o.obj_circ == o) && (o.circ == o.circ.me); } catch(e) { } return val; } function testRegExp(f) { let o = { re: /a[0-9]+/, }; let val = false; try{ let c = f(o); val = (String(c.re) == String(/a[0-9]+/)); } catch(e) { } return val; } function testDate(f) { let o = { date: new Date(), }; let val = false; try{ let c = f(o); val = (+new Date(c.date) == +new Date(o.date)); } catch(e) { } return val; } function testBigInt(f) { let val = false; try{ let o = { big: 123n, }; let c = f(o); val = o.big == c.big; } catch(e) { } return val; } function log(f) { let o = getCase(); // orginal object let oB = getCase(); // "backup" used for shallow valid test let c1 = f(o); // copy 1 for reference let c2 = f(o); // copy 2 for test shallow values let c3 = f(o); // copy 3 for test deep values let is_proper_copy = deepCompare(c1,o); // shoud be true // shallow changes let testShallow = [ ['bool',false],['num',666],['str','xyz'],['arr',[]],['obj',{}] ] .reduce((acc,curr)=> acc && check(c1,c2,curr[0], curr[1]), true ); // should be true (original object shoud not have changed shallow fields) let is_valid = deepCompare(o,oB); // deep test (intruduce some change) if (c3.arr[6]) c3.arr[6][7].num = 777; let diff_shallow = !testShallow; // shoud be true (shallow field was copied) let diff_deep = !deepCompare(c1,c3); // shoud be true (deep field was copied) let can_copy_functions = testFunc(f); let can_copy_circular = testCirc(f); let can_copy_regexp = testRegExp(f); let can_copy_date = testDate(f); let can_copy_bigInt = testBigInt(f); let has_undefined = 'undef' in c1; // field with undefined value is copied? let is_ok = is_valid && is_proper_copy; let b=(bool) => (bool+'').padEnd(5,' '); // bool value to formated string testFunc(f); if(is_ok) { console.log(`${f.name} ${b(diff_shallow)} ${b(diff_deep)} ${b(can_copy_functions)} ${b(can_copy_circular)} ${b(has_undefined)} ${b(can_copy_date)} ${b(can_copy_regexp)} ${b(can_copy_bigInt)}`) } else { console.log(`${f.name}: INVALID ${is_valid} ${is_proper_copy}`,{c1}) } }

 <script src="https://code.jquery.com/jquery-3.5.0.min.js" integrity="sha256-xNzN2a4ltkB44Mc/Jz3pT4iU1cmeR0FkXs4pru/JxaQ=" crossorigin="anonymous"></script> <script src="https://cdn.jsdelivr.net/npm/lodash@4.17.15/lodash.min.js"></script> This snippet only presents tested solutions and show differences between them (but it no make performence tests)

Below there are example results for Chrome for shallow-big object

Answer 20

使用 Lodash：

var y = _.clone(x, true);

Answer 21

In ES-6 you can simply use Object.assign(...). Ex:

let obj = {person: 'Thor Odinson'};
let clone = Object.assign({}, obj);

A good reference is here: https://googlechrome.github.io/samples/object-assign-es6/

Answer 22

Interested in cloning simple objects:

JSON.parse(JSON.stringify(json_original));

Source : How to copy JavaScript object to new variable NOT by reference?

Answer 23

You can clone an object and remove any reference from the previous one using a single line of code. Simply do:

var obj1 = { text: 'moo1' };
var obj2 = Object.create(obj1); // Creates a new clone without references

obj2.text = 'moo2'; // Only updates obj2's text property

console.log(obj1, obj2); // Outputs: obj1: {text:'moo1'}, obj2: {text:'moo2'}

For browsers / engines that do not currently support Object.create you can use this polyfill:

// Polyfill Object.create if it does not exist
if (!Object.create) {
    Object.create = function (o) {
        var F = function () {};
        F.prototype = o;
        return new F();
    };
}

Answer 24

let clone = Object.assign( Object.create( Object.getPrototypeOf(obj)), obj)

ES6 解决方案，如果你想（浅）克隆一个类实例而不仅仅是一个属性对象。

Answer 25

New answer to an old question! If you have the pleasure of having using ECMAScript 2016 (ES6) with Spread Syntax , it's easy.

keepMeTheSame = {first: "Me!", second: "You!"};
cloned = {...keepMeTheSame}

This provides a clean method for a shallow copy of an object. Making a deep copy, meaning makign a new copy of every value in every recursively nested object, requires on of the heavier solutions above.

JavaScript keeps evolving.

Answer 26

Structured Cloning

2022 update: The structuredClone() global function is already available in Node 17, Deno 1.14, and most major browsers (see Can I Use ).

You can use the same structured clone mechanism that the HTML standard includes for sending data between realms.

const clone = structuredClone(original);

See the other answer for more details.

Answer 27

I think there is a simple and working answer. In deep copying there are two concerns:

1. Keep properties independent to each other.
2. And keep the methods alive on cloned object.

So I think one simple solution will be to first serialize and deserialize and then do an assign on it to copy functions too.

let deepCloned = JSON.parse(JSON.stringify(source));
let merged = Object.assign({}, source);
Object.assign(merged, deepCloned);

Although this question has many answers, I hope this one helps too.

Answer 28

For a deep copy and clone, JSON.stringify then JSON.parse the object:

obj = { a: 0 , b: { c: 0}};
let deepClone = JSON.parse(JSON.stringify(obj));
obj.a = 5;
obj.b.c = 5;
console.log(JSON.stringify(deepClone)); // { a: 0, b: { c: 0}}

Answer 29

(The following was mainly an integration of @ Maciej Bukowski , @ A. Levy , @ Jan Turoň , @ Redu 's answers, and @ LeviRoberts , @ RobG 's comments, many thanks to them!!!)

Deep copy ? — YES! (mostly);
Shallow copy ? — NO! (except Proxy ).

I sincerely welcome everyone to test clone() .
In addition, defineProp() is designed to easily and quickly (re)define or copy any type of descriptor.

Function

function clone(object) {
  /*
    Deep copy objects by value rather than by reference,
    exception: `Proxy`
  */

  const seen = new WeakMap()

  return clone(object)


  function clone(object) {
    if (object !== Object(object)) return object /*
    —— Check if the object belongs to a primitive data type */

    if (object instanceof Node) return object.cloneNode(true) /*
    —— Clone DOM trees */

    let _object // The clone of object

    switch (object.constructor) {
      case Array:
      case Object:
        _object = cloneObject(object)
        break

      case Date:
        _object = new Date(+object)
        break

      case Function:
        _object = copyFn(object)
        break

      case RegExp:
        _object = new RegExp(object)
        break

      default:
        switch (Object.prototype.toString.call(object.constructor)) {
          //                                  // Stem from:
          case "[object Function]":
            switch (object[Symbol.toStringTag]) {
              case undefined:
                _object = cloneObject(object) // `class`
                break

              case "AsyncFunction":
              case "GeneratorFunction":
              case "AsyncGeneratorFunction":
                _object = copyFn(object)
                break

              default:
                _object = object
            }
            break

          case "[object Undefined]":          // `Object.create(null)`
            _object = cloneObject(object)
            break

          default:
            _object = object                  // `Proxy`
        }
    }

    return _object
  }


  function cloneObject(object) {
    if (seen.has(object)) return seen.get(object) /*
    —— Handle recursive references (circular structures) */

    const _object = Array.isArray(object)
      ? []
      : Object.create(Object.getPrototypeOf(object)) /*
        —— Assign [[Prototype]] for inheritance */

    seen.set(object, _object) /*
    —— Make `_object` the associative mirror of `object` */

    Reflect.ownKeys(object).forEach(key =>
      defineProp(_object, key, { value: clone(object[key]) }, object)
    )

    return _object
  }
}


function copyPropDescs(target, source) {
  Object.defineProperties(target,
    Object.getOwnPropertyDescriptors(source)
  )
}


function convertFnToStr(fn) {
  let fnStr = String(fn)
  if (fn.name.startsWith("[")) // isSymbolKey
    fnStr = fnStr.replace(/\[Symbol\..+?\]/, '')
  fnStr = /^(?!(async )?(function\b|[^{]+?=>))[^(]+?\(/.test(fnStr)
    ? fnStr.replace(/^(async )?(\*)?/, "$1function$2 ") : fnStr
  return fnStr
}

function copyFn(fn) {
  const newFn = new Function(`return ${convertFnToStr(fn)}`)()
  copyPropDescs(newFn, fn)
  return newFn
}



function defineProp(object, key, descriptor = {}, copyFrom = {}) {
  const { configurable: _configurable, writable: _writable }
    = Object.getOwnPropertyDescriptor(object, key)
    || { configurable: true, writable: true }

  const test = _configurable // Can redefine property
    && (_writable === undefined || _writable) // Can assign to property

  if (!test || arguments.length <= 2) return test

  const basisDesc = Object.getOwnPropertyDescriptor(copyFrom, key)
    || { configurable: true, writable: true } // Custom…
    || {}; // …or left to native default settings

  ["get", "set", "value", "writable", "enumerable", "configurable"]
    .forEach(attr =>
      descriptor[attr] === undefined &&
      (descriptor[attr] = basisDesc[attr])
    )

  const { get, set, value, writable, enumerable, configurable }
    = descriptor

  return Object.defineProperty(object, key, {
    enumerable, configurable, ...get || set
      ? { get, set } // Accessor descriptor
      : { value, writable } // Data descriptor
  })
}

// Tests

const obj0 = {
  u: undefined,
  nul: null,
  t: true,
  num: 9,
  str: "",
  sym: Symbol("symbol"),
  [Symbol("e")]: Math.E,
  arr: [[0], [1, 2]],
  d: new Date(),
  re: /f/g,
  get g() { return 0 },
  o: {
    n: 0,
    o: { f: function (...args) { } }
  },
  f: {
    getAccessorStr(object) {
      return []
        .concat(...
          Object.values(Object.getOwnPropertyDescriptors(object))
            .filter(desc => desc.writable === undefined)
            .map(desc => Object.values(desc))
        )
        .filter(prop => typeof prop === "function")
        .map(String)
    },
    f0: function f0() { },
    f1: function () { },
    f2: a => a / (a + 1),
    f3: () => 0,
    f4(params) { return param => param + params },
    f5: (a, b) => ({ c = 0 } = {}) => a + b + c
  }
}

defineProp(obj0, "s", { set(v) { this._s = v } })
defineProp(obj0.arr, "tint", { value: { is: "non-enumerable" } })
obj0.arr[0].name = "nested array"


let obj1 = clone(obj0)
obj1.o.n = 1
obj1.o.o.g = function g(a = 0, b = 0) { return a + b }
obj1.arr[1][1] = 3
obj1.d.setTime(+obj0.d + 60 * 1000)
obj1.arr.tint.is = "enumerable? no"
obj1.arr[0].name = "a nested arr"
defineProp(obj1, "s", { set(v) { this._s = v + 1 } })
defineProp(obj1.re, "multiline", { value: true })

console.log("\n\n" + "-".repeat(2 ** 6))




console.log(">:>: Test - Routinely")

console.log("obj0:\n ", JSON.stringify(obj0))
console.log("obj1:\n ", JSON.stringify(obj1))
console.log()

console.log("obj0:\n ", obj0)
console.log("obj1:\n ", obj1)
console.log()

console.log("obj0\n ",
  ".arr.tint:", obj0.arr.tint, "\n ",
  ".arr[0].name:", obj0.arr[0].name
)
console.log("obj1\n ",
  ".arr.tint:", obj1.arr.tint, "\n ",
  ".arr[0].name:", obj1.arr[0].name
)
console.log()

console.log("Accessor-type descriptor\n ",
  "of obj0:", obj0.f.getAccessorStr(obj0), "\n ",
  "of obj1:", obj1.f.getAccessorStr(obj1), "\n ",
  "set (obj0 & obj1) .s :", obj0.s = obj1.s = 0, "\n ",
  "  → (obj0 , obj1) ._s:", obj0._s, ",", obj1._s
)

console.log("—— obj0 has not been interfered.")

console.log("\n\n" + "-".repeat(2 ** 6))




console.log(">:>: Test - More kinds of functions")

const fnsForTest = {
  f(_) { return _ },
  func: _ => _,
  aFunc: async _ => _,
  async function() { },
  async asyncFunc() { },
  aFn: async function () { },
  *gen() { },
  async *asyncGen() { },
  aG1: async function* () { },
  aG2: async function* gen() { },
  *[Symbol.iterator]() { yield* Object.keys(this) }
}

console.log(Reflect.ownKeys(fnsForTest).map(k =>
  `${String(k)}:
  ${fnsForTest[k].name}-->
    ${String(fnsForTest[k])}`
).join("\n"))

const normedFnsStr = `{
  f: function f(_) { return _ },
  func: _ => _,
  aFunc: async _ => _,
  function: async function() { },
  asyncFunc: async function asyncFunc() { },
  aFn: async function () { },
  gen: function* gen() { },
  asyncGen: async function* asyncGen() { },
  aG1: async function* () { },
  aG2: async function* gen() { },
  [Symbol.iterator]: function* () { yield* Object.keys(this) }
}`

const copiedFnsForTest = clone(fnsForTest)
console.log("fnsForTest:", fnsForTest)
console.log("fnsForTest (copied):", copiedFnsForTest)
console.log("fnsForTest (normed str):", eval(`(${normedFnsStr})`))
console.log("Comparison of fnsForTest and its clone:",
  Reflect.ownKeys(fnsForTest).map(k =>
    [k, fnsForTest[k] === copiedFnsForTest[k]]
  )
)

console.log("\n\n" + "-".repeat(2 ** 6))




console.log(">:>: Test - Circular structures")

obj0.o.r = {}
obj0.o.r.recursion = obj0.o
obj0.arr[1] = obj0.arr

obj1 = clone(obj0)
console.log("obj0:\n ", obj0)
console.log("obj1:\n ", obj1)

console.log("Clear obj0's recursion:",
  obj0.o.r.recursion = null, obj0.arr[1] = 1
)
console.log(
  "obj0\n ",
  ".o.r:", obj0.o.r, "\n ",
  ".arr:", obj0.arr
)
console.log(
  "obj1\n ",
  ".o.r:", obj1.o.r, "\n ",
  ".arr:", obj1.arr
)
console.log("—— obj1 has not been interfered.")


console.log("\n\n" + "-".repeat(2 ** 6))




console.log(">:>: Test - Classes")

class Person {
  constructor(name) {
    this.name = name
  }
}

class Boy extends Person { }
Boy.prototype.sex = "M"

const boy0 = new Boy
boy0.hobby = { sport: "spaceflight" }

const boy1 = clone(boy0)
boy1.hobby.sport = "superluminal flight"

boy0.name = "one"
boy1.name = "neo"

console.log("boy0:\n ", boy0)
console.log("boy1:\n ", boy1)
console.log("boy1's prototype === boy0's:",
  Object.getPrototypeOf(boy1) === Object.getPrototypeOf(boy0)
)

References

1. Object.create() | MDN
2. Object.defineProperties() | MDN
3. Enumerability and ownership of properties | MDN
4. TypeError: cyclic object value | MDN

Language tricks used

1. Conditionally add prop to object

Answer 30

Use lodash _.cloneDeep().

Shallow Copy: lodash _.clone()

A shallow copy can be made by simply copying the reference.

let obj1 = {
    a: 0,
    b: {
        c: 0,
        e: {
            f: 0
        }
    }
};
let obj3 = _.clone(obj1);
obj1.a = 4;
obj1.b.c = 4;
obj1.b.e.f = 100;

console.log(JSON.stringify(obj1));
//{"a":4,"b":{"c":4,"e":{"f":100}}}

console.log(JSON.stringify(obj3));
//{"a":0,"b":{"c":4,"e":{"f":100}}}

Deep Copy: lodash _.cloneDeep()

fields are dereferenced: rather than references to objects being copied

let obj1 = {
    a: 0,
    b: {
        c: 0,
        e: {
            f: 0
        }
    }
};
let obj3 = _.cloneDeep(obj1);
obj1.a = 100;
obj1.b.c = 100;
obj1.b.e.f = 100;

console.log(JSON.stringify(obj1));
{"a":100,"b":{"c":100,"e":{"f":100}}}

console.log(JSON.stringify(obj3));
{"a":0,"b":{"c":0,"e":{"f":0}}}

Answer 31

The most correct to copy object is use Object.create :

Object.create(Object.getPrototypeOf(obj), Object.getOwnPropertyDescriptors(obj));

Such notation will make identically the same object with correct prototype and hidden properties.

Answer 32

This is an adaptation of A. Levy's code to also handle the cloning of functions and multiple/cyclic references - what this means is that if two properties in the tree which is cloned are references of the same object, the cloned object tree will have these properties point to one and the same clone of the referenced object. This also solves the case of cyclic dependencies which, if left unhandled, leads to an infinite loop. The complexity of the algorithm is O(n)

function clone(obj){
    var clonedObjectsArray = [];
    var originalObjectsArray = []; //used to remove the unique ids when finished
    var next_objid = 0;

    function objectId(obj) {
        if (obj == null) return null;
        if (obj.__obj_id == undefined){
            obj.__obj_id = next_objid++;
            originalObjectsArray[obj.__obj_id] = obj;
        }
        return obj.__obj_id;
    }

    function cloneRecursive(obj) {
        if (null == obj || typeof obj == "string" || typeof obj == "number" || typeof obj == "boolean") return obj;

        // Handle Date
        if (obj instanceof Date) {
            var copy = new Date();
            copy.setTime(obj.getTime());
            return copy;
        }

        // Handle Array
        if (obj instanceof Array) {
            var copy = [];
            for (var i = 0; i < obj.length; ++i) {
                copy[i] = cloneRecursive(obj[i]);
            }
            return copy;
        }

        // Handle Object
        if (obj instanceof Object) {
            if (clonedObjectsArray[objectId(obj)] != undefined)
                return clonedObjectsArray[objectId(obj)];

            var copy;
            if (obj instanceof Function)//Handle Function
                copy = function(){return obj.apply(this, arguments);};
            else
                copy = {};

            clonedObjectsArray[objectId(obj)] = copy;

            for (var attr in obj)
                if (attr != "__obj_id" && obj.hasOwnProperty(attr))
                    copy[attr] = cloneRecursive(obj[attr]);                 

            return copy;
        }       


        throw new Error("Unable to copy obj! Its type isn't supported.");
    }
    var cloneObj = cloneRecursive(obj);



    //remove the unique ids
    for (var i = 0; i < originalObjectsArray.length; i++)
    {
        delete originalObjectsArray[i].__obj_id;
    };

    return cloneObj;
}

Some quick tests

var auxobj = {
    prop1 : "prop1 aux val", 
    prop2 : ["prop2 item1", "prop2 item2"]
    };

var obj = new Object();
obj.prop1 = "prop1_value";
obj.prop2 = [auxobj, auxobj, "some extra val", undefined];
obj.nr = 3465;
obj.bool = true;

obj.f1 = function (){
    this.prop1 = "prop1 val changed by f1";
};

objclone = clone(obj);

//some tests i've made
console.log("test number, boolean and string cloning: " + (objclone.prop1 == obj.prop1 && objclone.nr == obj.nr && objclone.bool == obj.bool));

objclone.f1();
console.log("test function cloning 1: " + (objclone.prop1 == 'prop1 val changed by f1'));
objclone.f1.prop = 'some prop';
console.log("test function cloning 2: " + (obj.f1.prop == undefined));

objclone.prop2[0].prop1 = "prop1 aux val NEW";
console.log("test multiple references cloning 1: " + (objclone.prop2[1].prop1 == objclone.prop2[0].prop1));
console.log("test multiple references cloning 2: " + (objclone.prop2[1].prop1 != obj.prop2[0].prop1));

Answer 33

I just wanted to add to all the Object.create solutions in this post, that this does not work in the desired way with nodejs.

In Firefox the result of

var a = {"test":"test"};
var b = Object.create(a);
console.log(b);´

is

{test:"test"} .

In nodejs it is

{}

Answer 34

function clone(src, deep) {

    var toString = Object.prototype.toString;
    if(!src && typeof src != "object"){
        //any non-object ( Boolean, String, Number ), null, undefined, NaN
        return src;
    }

    //Honor native/custom clone methods
    if(src.clone && toString.call(src.clone) == "[object Function]"){
        return src.clone(deep);
    }

    //DOM Elements
    if(src.nodeType && toString.call(src.cloneNode) == "[object Function]"){
        return src.cloneNode(deep);
    }

    //Date
    if(toString.call(src) == "[object Date]"){
        return new Date(src.getTime());
    }

    //RegExp
    if(toString.call(src) == "[object RegExp]"){
        return new RegExp(src);
    }

    //Function
    if(toString.call(src) == "[object Function]"){
        //Wrap in another method to make sure == is not true;
        //Note: Huge performance issue due to closures, comment this :)
        return (function(){
            src.apply(this, arguments);
        });

    }

    var ret, index;
    //Array
    if(toString.call(src) == "[object Array]"){
        //[].slice(0) would soft clone
        ret = src.slice();
        if(deep){
            index = ret.length;
            while(index--){
                ret[index] = clone(ret[index], true);
            }
        }
    }
    //Object
    else {
        ret = src.constructor ? new src.constructor() : {};
        for (var prop in src) {
            ret[prop] = deep
                ? clone(src[prop], true)
                : src[prop];
        }
    }

    return ret;
};

Answer 35

Since mindeavor stated that the object to be cloned is a 'literal-constructed' object, a solution might be to simply generate the object multiple times rather than cloning an instance of the object:

function createMyObject()
{
    var myObject =
    {
        ...
    };
    return myObject;
}

var myObjectInstance1 = createMyObject();
var myObjectInstance2 = createMyObject();

Answer 36

I've written my own implementation. Not sure if it counts as a better solution:

/*
    a function for deep cloning objects that contains other nested objects and circular structures.
    objects are stored in a 3D array, according to their length (number of properties) and their depth in the original object.
                                    index (z)
                                         |
                                         |
                                         |
                                         |
                                         |
                                         |                      depth (x)
                                         |_ _ _ _ _ _ _ _ _ _ _ _
                                        /_/_/_/_/_/_/_/_/_/
                                       /_/_/_/_/_/_/_/_/_/
                                      /_/_/_/_/_/_/...../
                                     /................./
                                    /.....            /
                                   /                 /
                                  /------------------
            object length (y)    /
*/

Following is the implementation:

function deepClone(obj) {
    var depth = -1;
    var arr = [];
    return clone(obj, arr, depth);
}

/**
 *
 * @param obj source object
 * @param arr 3D array to store the references to objects
 * @param depth depth of the current object relative to the passed 'obj'
 * @returns {*}
 */
function clone(obj, arr, depth){
    if (typeof obj !== "object") {
        return obj;
    }

    var length = Object.keys(obj).length; // native method to get the number of properties in 'obj'

    var result = Object.create(Object.getPrototypeOf(obj)); // inherit the prototype of the original object
    if(result instanceof Array){
        result.length = length;
    }

    depth++; // depth is increased because we entered an object here

    arr[depth] = []; // this is the x-axis, each index here is the depth
    arr[depth][length] = []; // this is the y-axis, each index is the length of the object (aka number of props)
    // start the depth at current and go down, cyclic structures won't form on depths more than the current one
    for(var x = depth; x >= 0; x--){
        // loop only if the array at this depth and length already have elements
        if(arr[x][length]){
            for(var index = 0; index < arr[x][length].length; index++){
                if(obj === arr[x][length][index]){
                    return obj;
                }
            }
        }
    }

    arr[depth][length].push(obj); // store the object in the array at the current depth and length
    for (var prop in obj) {
        if (obj.hasOwnProperty(prop)) result[prop] = clone(obj[prop], arr, depth);
    }

    return result;
}

Answer 37

Use deepcopy from npm . Works in both the browser and in node as an npm module...

https://www.npmjs.com/package/deepcopy

let a = deepcopy(b)

Answer 38

Object copy using ( ... )

//bad
const original = { a: 1, b: 2 };
const copy = Object.assign({}, original, { c: 3 }); // copy => { a: 1, b: 2,c: 3 }

//good
const originalObj = { id: 5, name: 'San Francisco'};
const copyObject = {...originalObj, pincode: 4444};
console.log(copyObject)  //{ id: 5, name: 'San Francisco', pincode: 4444 }

Same can be use for copying array from one to other

const itemsCopy = [...items];

Answer 39

Simple recursive method to clone an object. Also could use lodash.clone.

 let clone = (obj) => { let obj2 = Array.isArray(obj) ? [] : {}; for(let k in obj) { obj2[k] = (typeof obj[k] === 'object' ) ? clone(obj[k]) : obj[k]; } return obj2; } let w = { name: "Apple", types: ["Fuji", "Gala"]}; let x = clone(w); w.name = "Orange"; w.types = ["Navel"]; console.log(x); console.log(w);

Answer 40

Native JS:

const shallowClone = {...originalObj};
const deepClone = JSON.parse(JSON.stringify(originalObj));

Using Libraries:

// Lodash
const shallowClone = _.clone(originalObj);
const deepClone = _. cloneDeep(originalObj);

// JQuery
const shallowClone = jQuery.extend({}, originalObj);
const deepClone = jQuery.extend(true, {}, originalObj);

// Angular
const deepClone = angular.copy(originalObj);

Answer 41

Jan Turoň's answer above is very close, and may be the best to use in a browser due to compatibility issues, but it will potentially cause some strange enumeration issues. For instance, executing:

for ( var i in someArray ) { ... }

Will assign the clone() method to i after iterating through the elements of the array. Here's an adaptation that avoids the enumeration and works with node.js:

Object.defineProperty( Object.prototype, "clone", {
    value: function() {
        if ( this.cloneNode )
        {
            return this.cloneNode( true );
        }

        var copy = this instanceof Array ? [] : {};
        for( var attr in this )
        {
            if ( typeof this[ attr ] == "function" || this[ attr ] == null || !this[ attr ].clone )
            {
                copy[ attr ] = this[ attr ];
            }
            else if ( this[ attr ] == this )
            {
                copy[ attr ] = copy;
            }
            else
            {
                copy[ attr ] = this[ attr ].clone();
            }
        }
        return copy;
    }
});

Object.defineProperty( Date.prototype, "clone", {
    value: function() {
        var copy = new Date();
        copy.setTime( this.getTime() );
        return copy;
    }
});

Object.defineProperty( Number.prototype, "clone", { value: function() { return this; } } );
Object.defineProperty( Boolean.prototype, "clone", { value: function() { return this; } } );
Object.defineProperty( String.prototype, "clone", { value: function() { return this; } } );

This avoids making the clone() method enumerable because defineProperty() defaults enumerable to false.

Answer 42

Consult http://www.w3.org/html/wg/drafts/html/master/infrastructure.html#safe-passing-of-structured-data for the W3C's "Safe passing of structured data" algorithm, intended to be implemented by browsers for passing data to eg web workers. However, it has some limitations, in that it does not handle functions. See https://developer.mozilla.org/en-US/docs/DOM/The_structured_clone_algorithm for more information, including an alternative algorithm in JS which gets you part of the way there.

Answer 43

Clone an object based on a template . What do you do if you don't want an exact copy, but you do want the robustness of some kind of reliable clone operation but you only want bits cloned or you want to make sure you can control the existence or format of each attribute value cloned?

I am contributing this because it's useful for us and we created it because we could not find something similar. You can use it to clone an object based on a template object which specifies what attributes of the object I want to clone, and the template allows for functions to transform those attributes into something different if they don't exist on the source object or however you want to handle the clone. If it's not useful I am sure someone can delete this answer.

   function isFunction(functionToCheck) {
       var getType = {};
       return functionToCheck && getType.toString.call(functionToCheck) === '[object Function]';
   }

   function cloneObjectByTemplate(obj, tpl, cloneConstructor) {
       if (typeof cloneConstructor === "undefined") {
           cloneConstructor = false;
       }
       if (obj == null || typeof (obj) != 'object') return obj;

       //if we have an array, work through it's contents and apply the template to each item...
       if (Array.isArray(obj)) {
           var ret = [];
           for (var i = 0; i < obj.length; i++) {
               ret.push(cloneObjectByTemplate(obj[i], tpl, cloneConstructor));
           }
           return ret;
       }

       //otherwise we have an object...
       //var temp:any = {}; // obj.constructor(); // we can't call obj.constructor because typescript defines this, so if we are dealing with a typescript object it might reset values.
       var temp = cloneConstructor ? new obj.constructor() : {};

       for (var key in tpl) {
           //if we are provided with a function to determine the value of this property, call it...
           if (isFunction(tpl[key])) {
               temp[key] = tpl[key](obj); //assign the result of the function call, passing in the value
           } else {
               //if our object has this property...
               if (obj[key] != undefined) {
                   if (Array.isArray(obj[key])) {
                       temp[key] = [];
                       for (var i = 0; i < obj[key].length; i++) {
                           temp[key].push(cloneObjectByTemplate(obj[key][i], tpl[key], cloneConstructor));
                       }
                   } else {
                       temp[key] = cloneObjectByTemplate(obj[key], tpl[key], cloneConstructor);
                   }
               }
           }
       }

       return temp;
   }

A simple way to call it would be like this:

var source = {
       a: "whatever",
       b: {
           x: "yeah",
           y: "haha"
       }
   };
   var template = {
       a: true, //we want to clone "a"
       b: {
           x: true //we want to clone "b.x" too
       }
   }; 
   var destination = cloneObjectByTemplate(source, template);

If you wanted to use a function to make sure an attribute is returned or to make sure it's a particular type, use a template like this. Instead of using { ID: true } we are providing a function which still just copies the ID attribute of the source object but it makes sure that it's a number even if it does not exist on the source object.

 var template = {
    ID: function (srcObj) {
        if(srcObj.ID == undefined){ return -1; }
        return parseInt(srcObj.ID.toString());
    }
}

Arrays will clone fine but if you want to you can have your own function handle those individual attributes too, and do something special like this:

 var template = {
    tags: function (srcObj) {
        var tags = [];
        if (process.tags != undefined) {
            for (var i = 0; i < process.tags.length; i++) {

                tags.push(cloneObjectByTemplate(
                  srcObj.tags[i],
                  { a : true, b : true } //another template for each item in the array
                );
            }
        }
        return tags;
    }
 }

So in the above, our template just copies the tags attribute of the source object if it exists, (it's assumed to be an array), and for each element in that array the clone function is called to individually clone it based on a second template which just copies the a and b attributes of each of those tag elements.

If you are taking objects in and out of node and you want to control which attributes of those objects are cloned then this is a great way of controlling that in node.js and the code works in the browser too.

Here is an example of it's use: http://jsfiddle.net/hjchyLt1/

Answer 44

According to the Airbnb JavaScript Style Guide with 404 contributors:

Prefer the object spread operator over Object.assign to shallow-copy objects. Use the object rest operator to get a new object with certain properties omitted.

// very bad
const original = { a: 1, b: 2 };
const copy = Object.assign(original, { c: 3 }); // this mutates `original` ಠ_ಠ
delete copy.a; // so does this

// bad
const original = { a: 1, b: 2 };
const copy = Object.assign({}, original, { c: 3 }); // copy => { a: 1, b: 2, c: 3 }

// good
const original = { a: 1, b: 2 };
const copy = { ...original, c: 3 }; // copy => { a: 1, b: 2, c: 3 }

const { a, ...noA } = copy; // noA => { b: 2, c: 3 }

Also I'd like to warn you that even though Airbnb hardly recommends the object spread operator approach. Keep in mind that Microsoft Edge still does not support this 2018 feature yet.

ES2016+ Compat table >>

Answer 45

Just as this link says use this code:

let clone = Object.create(Object.getPrototypeOf(obj),
 Object.getOwnPropertyDescriptors(obj));

Answer 46

Simple

var restore = { name:'charlesi',
age:9}
var prev_data ={
name: 'charles'
age : 10
}

var temp = JSON.stringify(prev_data)
restore = JSON.parse(temp)

restore = {
name:'charlie',
age : 12}

output prev_data:

{
name: 'charles'
age : 10
} 

Answer 47

In my code I frequently define a function (_) to handle copies so that I can pass by value to functions. This code creates a deep copy but maintains inheritance. It also keeps track of sub-copies so that self-referential objects can be copied without an infinite loop. Feel free to use it.

It might not be the most elegant, but it hasn't failed me yet.

_ = function(oReferance) {
  var aReferances = new Array();
  var getPrototypeOf = function(oObject) {
    if(typeof(Object.getPrototypeOf)!=="undefined") return Object.getPrototypeOf(oObject);
    var oTest = new Object();
    if(typeof(oObject.__proto__)!=="undefined"&&typeof(oTest.__proto__)!=="undefined"&&oTest.__proto__===Object.prototype) return oObject.__proto__;
    if(typeof(oObject.constructor)!=="undefined"&&typeof(oTest.constructor)!=="undefined"&&oTest.constructor===Object&&typeof(oObject.constructor.prototype)!=="undefined") return oObject.constructor.prototype;
    return Object.prototype;
  };
  var recursiveCopy = function(oSource) {
    if(typeof(oSource)!=="object") return oSource;
    if(oSource===null) return null;
    for(var i=0;i<aReferances.length;i++) if(aReferances[i][0]===oSource) return aReferances[i][1];
    var Copy = new Function();
    Copy.prototype = getPrototypeOf(oSource);
    var oCopy = new Copy();
    aReferances.push([oSource,oCopy]);
    for(sPropertyName in oSource) if(oSource.hasOwnProperty(sPropertyName)) oCopy[sPropertyName] = recursiveCopy(oSource[sPropertyName]);
    return oCopy;
  };
  return recursiveCopy(oReferance);
};

// Examples:
Wigit = function(){};
Wigit.prototype.bInThePrototype = true;
A = new Wigit();
A.nCoolNumber = 7;
B = _(A);
B.nCoolNumber = 8; // A.nCoolNumber is still 7
B.bInThePrototype // true
B instanceof Wigit // true

Answer 48

You can use functional closure to gain all the benefits of a deep copy, without a deep copy. It's a very different paradigm, but works well. Instead of trying to copy an existing object, just use a function to instantiate a new object when you need one.

First, create an function that returns an object

function template() {
  return {
    values: [1, 2, 3],
    nest: {x: {a: "a", b: "b"}, y: 100}
  };
}

Then create a simple shallow copy function

function copy(a, b) {
  Object.keys(b).forEach(function(key) {
    a[key] = b[key];
  });
}

Create a new object, and copy the template's properties onto it

var newObject = {}; 
copy(newObject, template());

But the above copy step is not necessary. All you need to do is this:

var newObject = template();

Now that you have a new object, test to see what its properties are:

console.log(Object.keys(newObject));

This displays:

["values", "nest"]

Yes, those are the newObject's own properties, not references to properties on another object. Let's just check:

console.log(newObject.nest.x.b);

This displays:

"b"

The newObject has acquired all of the template object's properties, but is free of any dependency chain.

http://jsbin.com/ISUTIpoC/1/edit?js,console

I added this example to encourage some debate, so please add some comments :)

Answer 49

I think, that recurrence with caching is the best what we can do it here without libraries.

And underestimated WeakMap comes to the problem of cycles, wherein storing pairs of references to old and new object can help us to recreate pretty easily whole tree.

I prevented deep cloning of the DOM elements, probably you don't want to clone entire page :)

function deepCopy(object) {
    const cache = new WeakMap(); // Map of old - new references

    function copy(obj) {
        if (typeof obj !== 'object' ||
            obj === null ||
            obj instanceof HTMLElement
        )
            return obj; // primitive value or HTMLElement

        if (obj instanceof Date) 
            return new Date().setTime(obj.getTime());

        if (obj instanceof RegExp) 
            return new RegExp(obj.source, obj.flags);

        if (cache.has(obj)) 
            return cache.get(obj);

        const result = obj instanceof Array ? [] : {};

        cache.set(obj, result); // store reference to object before the recursive starts

        if (obj instanceof Array) {
            for(const o of obj) {
                 result.push(copy(o));
            }
            return result;
        }

        const keys = Object.keys(obj); 

        for (const key of keys)
            result[key] = copy(obj[key]);

        return result;
    }

    return copy(object);
}

Some tests:

// #1
const obj1 = { };
const obj2 = { };
obj1.obj2 = obj2;
obj2.obj1 = obj1; // Trivial circular reference

var copy = deepCopy(obj1);
copy == obj1 // false
copy.obj2 === obj1.obj2 // false
copy.obj2.obj1.obj2 // and so on - no error (correctly cloned).

// #2
const obj = { x: 0 }
const clone = deepCopy({ a: obj, b: obj });
clone.a == clone.b // true

// #3
const arr = [];
arr[0] = arr; // A little bit weird but who cares
clone = deepCopy(arr)
clone == arr // false;
clone[0][0][0][0] == clone // true;

NOTE: I'm using constants, for of loop, => operator and WeakMaps to create more essential code. This syntax (ES6) is supported by today's browsers

Answer 50

The solution JSON.parse(JSON.stringify(orig_obj) as stated by many peers here for deep_cloning has several issues which I found, and they are listed below:

1. It discards the entries while copying whose values are undefined in the original object,
2. If there are some values like Infinity , NaN etc, they will be converted into null while copying,
3. If there is a Date type in the original object, it will be stringified in the cloned object ( typeof date_entry --> string ).

Found an effective way for cloning an object, and it worked well for me in all sort of scenarios. Please have a look at below code, as it has resolved all above mentioned pitfalls of JSON.parse(...) , yet resulting in proper deep-cloning:

var orig_obj = {
  string: 'my_str',
  number: 123,
  bool: false,
  nul: null,
  nested : {
    value : true
  },
  nan : NaN,
  date: new Date(), 
  undef: undefined,
  inf: Infinity,
}
console.log("original_obj before modification: ", orig_obj, "\n");
console.log(typeof orig_obj.date, "\n");

var clone_obj = Object.assign({}, orig_obj);

//this below loop will help in deep cloning and solving above issues
for(let prop in orig_obj) {
    if(typeof orig_obj[prop] === "object") {
        if(orig_obj[prop] instanceof Date)
            clone_obj[prop] = orig_obj[prop];
        else {
            clone_obj[prop] = JSON.parse(JSON.stringify(orig_obj[prop]));
        }
    }
}

console.log("cloned_obj before modification: ", orig_obj, "\n");

clone_obj.bool = true;
clone_obj.nested.value = "false";

console.log("original_obj post modification: ", orig_obj, "\n");
console.log("cloned_obj post modification: ", clone_obj, "\n");
console.log(typeof clone_obj.date);

Answer 51

I've tried this in the case of a scalar object and it works for me:

function binder(i) {
  return function () {
    return i;
  };
}

a=1;
b=binder(a)(); // copy value of a into b

alert(++a); // 2
alert(b); // still 1

Regards.

Answer 52

Here's a modern solution that doesn't have the pitfalls of Object.assign() (does not copy by reference):

const cloneObj = (obj) => {
    return Object.keys(obj).reduce((dolly, key) => {
        dolly[key] = (obj[key].constructor === Object) ?
            cloneObj(obj[key]) :
            obj[key];
        return dolly;
    }, {});
};

Answer 53

Using defaults (historically specific to nodejs but now usable from the browser thanks to modern JS):

import defaults from 'object.defaults';

const myCopy = defaults({}, myObject);

Answer 54

To support a better understanding of copying of objects, this illustrative jsbin may be of value

class base {
  get under(){return true}
}

class a extends base {}

const b = {
  get b1(){return true},
  b: true
}

console.log('Object assign')
let t1 = Object.create(b)
t1.x = true
const c = Object.assign(t1, new a())
console.log(c.b1 ? 'prop value copied': 'prop value gone')
console.log(c.x ? 'assigned value copied': 'assigned value gone')
console.log(c.under ? 'inheritance ok': 'inheritance gone')
console.log(c.b1 ? 'get value unchanged' : 'get value lost')
c.b1 = false
console.log(c.b1? 'get unchanged' : 'get lost')
console.log('-----------------------------------')
console.log('Object assign  - order swopped')
t1 = Object.create(b)
t1.x = true
const d = Object.assign(new a(), t1)
console.log(d.b1 ? 'prop value copied': 'prop value gone')
console.log(d.x ? 'assigned value copied': 'assigned value gone')
console.log(d.under ? 'inheritance n/a': 'inheritance gone')
console.log(d.b1 ? 'get value copied' : 'get value lost')
d.b1 = false
console.log(d.b1? 'get copied' : 'get lost')
console.log('-----------------------------------')
console.log('Spread operator')
t1 = Object.create(b)
t2 = new a()
t1.x = true
const e = { ...t1, ...t2 }
console.log(e.b1 ? 'prop value copied': 'prop value gone')
console.log(e.x ? 'assigned value copied': 'assigned value gone')
console.log(e.under ? 'inheritance ok': 'inheritance gone')
console.log(e.b1 ? 'get value copied' : 'get value lost')
e.b1 = false
console.log(e.b1? 'get copied' : 'get lost')
console.log('-----------------------------------')
console.log('Spread operator on getPrototypeOf')
t1 = Object.create(b)
t2 = new a()
t1.x = true
const e1 = { ...Object.getPrototypeOf(t1), ...Object.getPrototypeOf(t2) }
console.log(e1.b1 ? 'prop value copied': 'prop value gone')
console.log(e1.x ? 'assigned value copied': 'assigned value gone')
console.log(e1.under ? 'inheritance ok': 'inheritance gone')
console.log(e1.b1 ? 'get value copied' : 'get value lost')
e1.b1 = false
console.log(e1.b1? 'get copied' : 'get lost')
console.log('-----------------------------------')
console.log('keys, defineProperty, getOwnPropertyDescriptor')
f = Object.create(b)
t2 = new a()
f.x = 'a'
Object.keys(t2).forEach(key=> {
  Object.defineProperty(f,key,Object.getOwnPropertyDescriptor(t2, key))
})
console.log(f.b1 ? 'prop value copied': 'prop value gone')
console.log(f.x ? 'assigned value copied': 'assigned value gone')
console.log(f.under ? 'inheritance ok': 'inheritance gone')
console.log(f.b1 ? 'get value copied' : 'get value lost')
f.b1 = false
console.log(f.b1? 'get copied' : 'get lost')
console.log('-----------------------------------')
console.log('defineProperties, getOwnPropertyDescriptors')
let g = Object.create(b)
t2 = new a()
g.x = 'a'
Object.defineProperties(g,Object.getOwnPropertyDescriptors(t2))
console.log(g.b1 ? 'prop value copied': 'prop value gone')
console.log(g.x ? 'assigned value copied': 'assigned value gone')
console.log(g.under ? 'inheritance ok': 'inheritance gone')
console.log(g.b1 ? 'get value copied' : 'get value lost')
g.b1 = false
console.log(g.b1? 'get copied' : 'get lost')
console.log('-----------------------------------')

Answer 55

I have gone through all above solutions and they are quite well. However, there is another approach that you can use to clone object (with values not reference). Object.assign

let x = {
    a: '1',
    b: '2'
}

let y = Object.assign({}, x)
y.a = "3"

console.log(x)

The output will be

{ a: '1', b: '2' }

Moreover, you can also clone array with the same approach.

clonedArray = Object.assign([], array)

Answer 56

Using the spread syntax performs a shallow copy of the object. This means that none of the nested object instances are cloned as you can see in the following example with the nested object child

 const user1 = { name: 'Alex', address: '15th Park Avenue', age: 43, child:{ name: 'John' } } const user2 = {...user1}; user1.child.name = 'chris'; console.log(user1); console.log(user2);

To solve this nested object problem and perform a deep copy we can use JSON.parse(JSON.stringify(someObject))

 const user1 = { name: 'Alex', address: '15th Park Avenue', age: 43, child:{ name: 'John' } } const user2 = JSON.parse(JSON.stringify(user1)); user1.child.name = 'chris'; console.log(user1); console.log(user2);

Answer 57

Ok so this might be the very best option for shallow copying. If follows the many examples using assign, but it also keeps the inheritance and prototype. It's so simple too and works for most array-like and Objects except those with constructor requirements or read-only properties. But that means it fails miserably for TypedArrays, RegExp, Date, Maps, Sets and Object versions of primitives (Boolean, String, etc..).

function copy ( a ) { return Object.assign( new a.constructor, a ) }

Where a can be any Object or class constructed instance, but again not be reliable for thingies that use specialized getters and setters or have constructor requirements, but for more simple situations it rocks. It does work on arguments as well.

You can also apply it to primitives to get strange results, but then... unless it just ends up being a useful hack, who cares.

results from basic built-in Object and Array...

> a = { a: 'A', b: 'B', c: 'C', d: 'D' }
{ a: 'A', b: 'B', c: 'C', d: 'D' }
> b = copy( a )
{ a: 'A', b: 'B', c: 'C', d: 'D' }
> a = [1,2,3,4]
[ 1, 2, 3, 4 ]
> b = copy( a )
[ 1, 2, 3, 4 ]

And fails because of mean get/setters, constructor required arguments or read-only properties, and sins against the father.

> a = /\w+/g
/\w+/g
> b = copy( a )  // fails because source and flags are read-only
/(?:)/
> a = new Date ( '1/1/2001' )
2000-12-31T16:00:00.000Z
> b = copy( a )  // fails because Date using methods to get and set things
2017-02-04T14:44:13.990Z
> a = new Boolean( true )
[Boolean: true]
> b = copy( a )  // fails because of of sins against the father
[Boolean: false]
> a = new Number( 37 )
[Number: 37]
> b = copy( a )  // fails because of of sins against the father
[Number: 0]
> a = new String( 'four score and seven years ago our four fathers' )
[String: 'four score and seven years ago our four fathers']
> b = copy( a )  // fails because of of sins against the father
{ [String: ''] '0': 'f', '1': 'o', '2': 'u', '3': 'r', '4': ' ', '5': 's', '6': 'c', '7': 'o', '8': 'r', '9': 'e', '10': ' ', '11': 'a', '12': 'n', '13': 'd', '14': ' ', '15': 's', '16': 'e', '17': 'v', '18': 'e', '19': 'n', '20': ' ', '21': 'y', '22': 'e', '23': 'a', '24': 'r', '25': 's', '26': ' ', '27': 'a', '28': 'g', '29': 'o', '30': ' ', '31': 'o', '32': 'u', '33': 'r', '34': ' ', '35': 'f', '36': 'o', '37': 'u', '38': 'r', '39': ' ', '40': 'f', '41': 'a', '42': 't', '43': 'h', '44': 'e', '45': 'r', '46': 's' } 

Answer 58

I don't know which cases this doesn't work for, but it got me a copy of an array. I think its cute :) Hope it helps

copiedArr = origArr.filter(function(x){return true})

Answer 59

If your object is a class (eg https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes ):

var copiedObject = jQuery.extend(true, {}, originalObject);
copiedObject.__proto__ = originalObject.__proto__;

Then in copiedObject you have a deep-copied instance of originalObject class with all its methods.

Answer 60

If you are using TypeScript, need to support older web browsers (and so can't use Object.assign ), and aren't using a library with a clone method build in, you can make yourself a combine helper in a few lines of code. It combines objects, and if you have only one, just clones it.

/** Creates a new object that combines the properties of the specified objects. */
function combine(...objs: {}[]) {
    const combined = {};
    objs.forEach(o => Object.keys(o).forEach(p => combined[p] = o[p]));
    return combined;
}

Answer 61

You may clone your Object without modification parent Object -

    /** [Object Extend]*/
    ( typeof Object.extend === 'function' ? undefined : ( Object.extend = function ( destination, source ) {
        for ( var property in source )
            destination[property] = source[property];
        return destination;
    } ) );
    /** [/Object Extend]*/
    /** [Object clone]*/
    ( typeof Object.clone === 'function' ? undefined : ( Object.clone = function ( object ) {
        return this.extend( {}, object );
    } ) );
    /** [/Object clone]*/

    let myObj = {
        a:1, b:2, c:3, d:{
            a:1, b:2, c:3
        }
    };

    let clone = Object.clone( myObj );

    clone.a = 10;

    console.log('clone.a==>', clone.a); //==> 10

    console.log('myObj.a==>', myObj.a); //==> 1 // object not modified here

    let clone2 = Object.clone( clone );

    clone2.a = 20;

    console.log('clone2.a==>', clone2.a); //==> 20

    console.log('clone.a==>', clone.a); //==> 10 // object not modified here

Answer 62

I'm providing an answer to this question, because I do not see any native, recursive implementations here that resolve the problem of DOM elements.

The problem there is that <element> has parent and child attributes, that link to other elements with parent and child values, which point back to the original <element> , causing either an infinite recursive or cyclic redundancy .

If your object is something safe and simple like

{
    '123':456
}

...then any other answer here will probably work.

But if you have...

{
    '123':<reactJSComponent>,
    '456':document.createElement('div'),
}

...then you need something like this:

    // cloneVariable() : Clone variable, return null for elements or components.
var cloneVariable = function (args) {
    const variable = args.variable;

    if(variable === null) {
            return null;
    }

    if(typeof(variable) === 'object') {
            if(variable instanceof HTMLElement || variable.nodeType > 0) {
                    return null;
            }

            if(Array.isArray(variable)) {
                    var arrayclone = [];

                    variable.forEach((element) => {
                            arrayclone.push(cloneVariable({'variable':element}));
                    });

                    return arrayclone;
            }

            var objectclone = {};

            Object.keys(variable).forEach((field) => {
                    objectclone[field] = cloneVariable({'variable':variable[field]});
            });

            return objectclone;
    }

    return variable;
}

Answer 63

var x = {'e': 2, 'd': 8, 'b': 5};

const y = {};
for(let key in x) {
    y[key] = x[key];
}
console.log(y); // =>>> {e: 2, d: 8, b: 5}

const z = {};
Object.keys(x).forEach(key => {
    z[key] = x[key];
});
console.log(z); // =>>> {e: 2, d: 8, b: 5}

const w = {};
for(let i = 0; i < Object.keys(x).length; i++) {
    w[Object.keys(x)[i]] = x[Object.keys(x)[i]];
}
console.log(w); // =>>> {e: 2, d: 8, b: 5}

const v = {};
for(let key of Object.keys(x)) {
    v[key] = x[key];
}
console.log(v); // =>>> {e: 2, d: 8, b: 5}

x['q'] = 100;   // Altering x will not affect the other objects

console.log(x); // =>>> {e: 2, d: 8, b: 5, q: 100}
console.log(y); // =>>> {e: 2, d: 8, b: 5}
console.log(z); // =>>> {e: 2, d: 8, b: 5}
console.log(w); // =>>> {e: 2, d: 8, b: 5}
console.log(v); // =>>> {e: 2, d: 8, b: 5}

Answer 64

Ways to Copy Objects in JavaScript

1. Use the spread ( ... ) syntax
2. Use the Object.assign() method
3. Use the JSON.stringify() and JSON.parse() methods

const person = {
    firstName: 'John',
    lastName: 'Doe'
};

// using spread ...
let p1 = {
    ...person
};

// using  Object.assign() method
let p2 = Object.assign({}, person);

// using JSON
let p3 = JSON.parse(JSON.stringify(person));

Answer 65

You can use rest operator to clone arrays or objects

let myObj = {1: 100, 'a': 200};

let clone = {...myObj}; 

clone.a = 300;

console.log(clone.a) // Output :- 300
console.log(myObj.a) // Output :- 200

Answer 66

This makes new copy of your obj (not just reference).

let myCopy = JSON.parse(JSON.stringify(obj)); 

..Works much efficiently then the _.cloneDeep(obj) .

Answer 67

If there are no circular dependencies in your object, I suggest using one of the other answers or jQuery's copy methods , as they all seem quite effective.

If there are circular dependencies (ie, two sub-objects link to each other), you are kind of screwed as there is (from a theoretical perspective) no way to solve this issue elegantly .

Answer 68

//
// creates 'clone' method on context object
//
//  var 
//     clon = Object.clone( anyValue );
//
!((function (propertyName, definition) {
    this[propertyName] = definition();
}).call(
    Object,
    "clone",
    function () {
        function isfn(fn) {
            return typeof fn === "function";
        }

        function isobj(o) {
            return o === Object(o);
        }

        function isarray(o) {
            return Object.prototype.toString.call(o) === "[object Array]";
        }

        function fnclon(fn) {
            return function () {
                fn.apply(this, arguments);
            };
        }

        function owns(obj, p) {
            return obj.hasOwnProperty(p);
        }

        function isemptyobj(obj) {
            for (var p in obj) {
                return false;
            }
            return true;
        }

        function isObject(o) {
            return Object.prototype.toString.call(o) === "[object Object]";
        }
        return function (input) {
            if (isfn(input)) {
                return fnclon(input);
            } else if (isobj(input)) {
                var cloned = {};
                for (var p in input) {
                    owns(Object.prototype, p)
                    || (
                        isfn(input[p])
                        && ( cloned[p] = function () { return input[p].apply(input, arguments); } )
                        || ( cloned[p] = input[p] )
                    );
                }
                if (isarray(input)) {
                    cloned.length = input.length;
                    "concat every filter forEach indexOf join lastIndexOf map pop push reduce reduceRight reverse shift slice some sort splice toLocaleString toString unshift"
                    .split(" ")
                    .forEach(
                      function (methodName) {
                        isfn( Array.prototype[methodName] )
                        && (
                            cloned[methodName] =
                            function () {
                                return Array.prototype[methodName].apply(cloned, arguments);
                            }
                        );
                      }
                    );
                }
                return isemptyobj(cloned)
                       ? (
                          isObject(input)
                          ? cloned
                          : input
                        )
                       : cloned;
            } else {
                return input;
            }
        };
    }
));
//

Answer 69

I came to this page due to the same question but I'm neither using JQuery and none of the clone-Methods worked for my own objects.

I'm aware my answer isn't related too strong to this question because it's a different approach. Instead of using clone-functions I use a create function. It worked for me for the following (unfortunately restricting) purposes:

1. I use mostly JSP-generated Javascript
2. I know in the beginning which Object must be generated (In my case it's Information from a Database which gets fetched once and needs to be deployed more often in the JS.

First I defined my Objects like this:

var obj= new Object();
obj.Type='Row';
obj.ID=1;
obj.Value='Blah blah';

Now I moved everything like:

function getObjSelektor(id_nummer,selected){
var obj = document.createElement("select");
obj.setAttribute("id","Selektor_"+id_nummer);
obj.setAttribute("name","Selektor");
obj.setAttribute("size","1");

var obj_opt_1 = document.createElement("option");
obj_opt_1.setAttribute("value","1");
if(1==selected)
    posopval_opt_1.setAttribute("selected","selected");
obj_opt_1.innerHTML="Blah blah";
obj.appendChild(obj_opt_1);

var obj_opt_2 = document.createElement("option");
obj_opt_2.setAttribute("value","2");
if(2==selected)
    obj_opt_2.setAttribute("selected","selected");
obj_opt_2.innerHTML="2nd Row";
obj.appendChild(obj_opt_2);

...

return obj;
}

And call the function in the regular code:

myDiv.getObjSelektor(getObjSelektor(anotherObject.ID));

As said this is a different approach which solved my issue for my purposes.

Answer 70

If you got an Object with Functions you can do it with JSONfn, see http://www.eslinstructor.net/jsonfn/ .

var obj= {
    name:'Marvin',
    getName :  function(){
      return this.name;
    }
}
var cobj = JSONfn.parse(JSONfn.stringify(obj));

Answer 71

The problem with copying an object that, eventually, may point at itself, can be solved with a simple check. Add this check, every time there is a copy action. It may be slow , but it should work.

I use a toType() function to return the object type, explicitly. I also have my own copyObj() function, which is rather similar in logic, which answers all three Object(), Array(), and Date() cases.

I run it in NodeJS.

NOT TESTED, YET.

// Returns true, if one of the parent's children is the target.
// This is useful, for avoiding copyObj() through an infinite loop!
function isChild(target, parent) {
  if (toType(parent) == '[object Object]') {
    for (var name in parent) {
      var curProperty = parent[name];

      // Direct child.
      if (curProperty = target) return true;

      // Check if target is a child of this property, and so on, recursively.
      if (toType(curProperty) == '[object Object]' || toType(curProperty) == '[object Array]') {
        if (isChild(target, curProperty)) return true;
      }
    }
  } else if (toType(parent) == '[object Array]') {
    for (var i=0; i < parent.length; i++) {
      var curItem = parent[i];

      // Direct child.
      if (curItem = target) return true;

      // Check if target is a child of this property, and so on, recursively.
      if (toType(curItem) == '[object Object]' || toType(curItem) == '[object Array]') {
        if (isChild(target, curItem)) return true;
      }
    }
  }

  return false;     // Not the target.
}

Answer 72

To handle circular objects that that JSON.stringify can't handle, you can bring in a library called JSOG , that serializes and deserializes arbitrary graphs into JSON format.

var clone = JSOG.parse(JSOG.stringify(original));

It might also be interesting to try patching JSOG for cloning with this trick (don't have time at the moment, but if someone wants to give it a shot...):

Serialize a simple function :

foo.f = function(a) { return a }
var stringForm = foo.f.toString() // "function (a) { return a }"

Deserialize a function :

eval("foo.f = " + stringForm)

Some conventions (probably in the name of the property) to identify functions vs regular strings would be needed ( @func_f perhaps).

Of course if the function calls a second function the second function will need to exist just as it would for the original.

The above however is quite dangerous if you are to accept the serialized form from an untrusted source, but then accepting any function in any form from an untrusted source would be dangerous, so if you're interested in cloning functions trust must have already been established (or you're already intent on writing a security flaw!).

Disclaimer: I have not tested the speed of JSOG stringify/parse vs JSON stringify/parse, but It does work on the simple (circular) objects I tested it with.

Answer 73

Ok, I know it has many answers, but no one pointed out, EcmaScript5 has assign method, work on FF and Chrome, it copies enumerable and own properties and Symbols.

Object Assign

Answer 74

所以只是添加一些简单的东西，如果你想创建一个灯箱或类似的东西，上面的大多数答案都是不必要的复杂，简单地复制源属性和其他任何必要的东西会更容易。

Answer 75

Short and sweet:

let clone = Object.fromEntries(Object.entries(obj));

Demo:

 let obj = {a: 'b'}; let clone = Object.fromEntries(Object.entries(obj)); clone.a = 'c'; console.log(obj, clone);

Answer 76

The different

Only copy top level: {...object} and Object.assign({}, object)

 let objA = { a: "keyA", b: { c: "keyC", } } let objB = Object.assign({}, objA); // or {...objB} // change objB objB.a = "Change objA.a (top)" console.log("objA.a (top) No Change:\n" + JSON.stringify(objA, false, 2)); objB.bc = "change should be only for objB.bc but it in objA.bc" console.log("objA.ac second level has Change:\n" + JSON.stringify(objA, false, 2));

for deep copy use structuredClone() 2022 or JSON.parse(JSON.stringify(object)) for old browser, easy without hack.

 let objA = { a: "keyA", b: { c: "keyC", } } let objB = typeof structuredClone == 'function' ? structuredClone(objA) : JSON.parse(JSON.stringify(objA)); // change objB objB.a = "Change objA.a (top)" objB.bc = "change should be only for objB.c but it in objA.c" console.log("objA has no Change:\n" + JSON.stringify(objA, false, 2));

Answer 77

From the Apple JavaScript Coding Guidelines :

// Create an inner object with a variable x whose default
// value is 3.
function innerObj()
{
        this.x = 3;
}
innerObj.prototype.clone = function() {
    var temp = new innerObj();
    for (myvar in this) {
        // this object does not contain any objects, so
        // use the lightweight copy code.
        temp[myvar] = this[myvar];
    }
    return temp;
}

// Create an outer object with a variable y whose default
// value is 77.
function outerObj()
{
        // The outer object contains an inner object.  Allocate it here.
        this.inner = new innerObj();
        this.y = 77;
}
outerObj.prototype.clone = function() {
    var temp = new outerObj();
    for (myvar in this) {
        if (this[myvar].clone) {
            // This variable contains an object with a
            // clone operator.  Call it to create a copy.
            temp[myvar] = this[myvar].clone();
        } else {
            // This variable contains a scalar value,
            // a string value, or an object with no
            // clone function.  Assign it directly.
            temp[myvar] = this[myvar];
        }
    }
    return temp;
}

// Allocate an outer object and assign non-default values to variables in
// both the outer and inner objects.
outer = new outerObj;
outer.inner.x = 4;
outer.y = 16;

// Clone the outer object (which, in turn, clones the inner object).
newouter = outer.clone();

// Verify that both values were copied.
alert('inner x is '+newouter.inner.x); // prints 4
alert('y is '+newouter.y); // prints 16

Steve

Answer 78

I've had an issue when copying objects. This is because when you do following, you're only making a 'reference' to the object and when the source object value is updated later, the copy object that was cloned also changes value because it was merely a 'reference' and hence you see multiple values of the last changes to the source object.

let x = { a: 1 };
let y = x; // y is a reference to x, so if x changes y also changes and v/v

So, to tackle this issue you do the following:

let y = JSON.parse(JSON.stringify(x)); //see Note below

The other way to prevent references is by doing the following:

let x = { a: 1 };
let y = Object.assign({}, x); // Object.assign(target, ...sources)

y.a = 2;
console.log(x); // { a: 1 }
console.log(y); // { a: 2 }

Note: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign#warning_for_deep_clone

Answer 79

I found a way to clone object with functions (break multiple lines to easier understand):

const clone = Object.assign(
    Object.create(
        Object.getPrototypeOf(originalObject)
    ),
    dataObject
);

Answer 80

My favorite & elegant JS objects clone solution is

function CloneObject() {}
function cloneObject(o) {
   CloneObject.prototype = o;
   return new CloneObject();
}

Use cloneObject(object) to get a clone of JS object.

Unlike many copy solutions this clone keeps prototype relationship in cloned object.

Answer 81

function clone(obj)
{
    var cloneObj = Object.create(obj);

    return cloneObj;
}

In Javascript objects individually inherit another object (Prototypal inheritance). Object.create(obj) returns an object that is a sub-object or child object of obj. In the above function it will effectively return a copy of the object.

However, This is a very odd way to clone because I am not using inheritance for its real purpose.