如何检查数组是否包含 JavaScript 中的值？

Question

What is the most concise and efficient way to find out if a JavaScript array contains a value?

This is the only way I know to do it:

function contains(a, obj) {
    for (var i = 0; i < a.length; i++) {
        if (a[i] === obj) {
            return true;
        }
    }
    return false;
}

Is there a better and more concise way to accomplish this?

This is very closely related to Stack Overflow question Best way to find an item in a JavaScript Array? which addresses finding objects in an array using indexOf .

Answer 1

Modern browsers have Array#includes , which does exactly that and is widely supported by everyone except IE:

 console.log(['joe', 'jane', 'mary'].includes('jane')); //true

You can also use Array#indexOf , which is less direct, but doesn't require polyfills for outdated browsers.

 console.log(['joe', 'jane', 'mary'].indexOf('jane') >= 0); //true

---

Many frameworks also offer similar methods:

• jQuery: $.inArray(value, array, [fromIndex])
• Underscore.js: _.contains(array, value) (also aliased as _.include and _.includes )
• Dojo Toolkit: dojo.indexOf(array, value, [fromIndex, findLast])
• Prototype: array.indexOf(value)
• MooTools: array.indexOf(value)
• MochiKit: findValue(array, value)
• MS Ajax: array.indexOf(value)
• Ext: Ext.Array.contains(array, value)
• Lodash: _.includes(array, value, [from]) (is _.contains prior 4.0.0)
• Ramda: R.includes(value, array)

Notice that some frameworks implement this as a function, while others add the function to the array prototype.

Answer 2

Update from 2019: This answer is from 2008 (11 years old!) and is not relevant for modern JS usage. The promised performance improvement was based on a benchmark done in browsers of that time. It might not be relevant to modern JS execution contexts. If you need an easy solution, look for other answers. If you need the best performance, benchmark for yourself in the relevant execution environments.

As others have said, the iteration through the array is probably the best way, but it has been proven that a decreasing while loop is the fastest way to iterate in JavaScript. So you may want to rewrite your code as follows:

function contains(a, obj) {
    var i = a.length;
    while (i--) {
       if (a[i] === obj) {
           return true;
       }
    }
    return false;
}

Of course, you may as well extend Array prototype:

Array.prototype.contains = function(obj) {
    var i = this.length;
    while (i--) {
        if (this[i] === obj) {
            return true;
        }
    }
    return false;
}

And now you can simply use the following:

alert([1, 2, 3].contains(2)); // => true
alert([1, 2, 3].contains('2')); // => false

Answer 3

indexOf maybe, but it's a "JavaScript extension to the ECMA-262 standard; as such it may not be present in other implementations of the standard."

Example:

[1, 2, 3].indexOf(1) => 0
["foo", "bar", "baz"].indexOf("bar") => 1
[1, 2, 3].indexOf(4) => -1

AFAICS Microsoft does not offer some kind of alternative to this, but you can add similar functionality to arrays in Internet Explorer (and other browsers that don't support indexOf ) if you want to, as a quick Google search reveals (for example, this one ).

Answer 4

The top answers assume primitive types but if you want to find out if an array contains an object with some trait, Array.prototype.some() is an elegant solution:

const items = [ {a: '1'}, {a: '2'}, {a: '3'} ]

items.some(item => item.a === '3')  // returns true
items.some(item => item.a === '4')  // returns false

The nice thing about it is that the iteration is aborted once the element is found so unnecessary iteration cycles are spared.

Also, it fits nicely in an if statement since it returns a boolean:

if (items.some(item => item.a === '3')) {
  // do something
}

* As jamess pointed out in the comment, at the time of this answer, September 2018, Array.prototype.some() is fully supported: caniuse.com support table

Answer 5

ECMAScript 7 introduces Array.prototype.includes .

It can be used like this:

[1, 2, 3].includes(2); // true
[1, 2, 3].includes(4); // false

It also accepts an optional second argument fromIndex :

[1, 2, 3].includes(3, 3); // false
[1, 2, 3].includes(3, -1); // true

Unlike indexOf , which uses Strict Equality Comparison , includes compares using SameValueZero equality algorithm. That means that you can detect if an array includes a NaN :

[1, 2, NaN].includes(NaN); // true

Also unlike indexOf , includes does not skip missing indices:

new Array(5).includes(undefined); // true

It can be polyfilled to make it work on all browsers.

Answer 6

Let's say you've defined an array like so:

const array = [1, 2, 3, 4]

Below are three ways of checking whether there is a 3 in there. All of them return either true or false .

Native Array method (since ES2016) ( compatibility table )

array.includes(3) // true

As custom Array method (pre ES2016)

// Prefixing the method with '_' to avoid name clashes
Object.defineProperty(Array.prototype, '_includes', { value: function (v) { return this.indexOf(v) !== -1 }})
array._includes(3) // true

Simple function

const includes = (a, v) => a.indexOf(v) !== -1
includes(array, 3) // true

Answer 7

Here's a JavaScript 1.6 compatible implementation of Array.indexOf :

if (!Array.indexOf) {
    Array.indexOf = [].indexOf ?
        function(arr, obj, from) {
            return arr.indexOf(obj, from);
        } :
        function(arr, obj, from) { // (for IE6)
            var l = arr.length,
                i = from ? parseInt((1 * from) + (from < 0 ? l : 0), 10) : 0;
            i = i < 0 ? 0 : i;
            for (; i < l; i++) {
                if (i in arr && arr[i] === obj) {
                    return i;
                }
            }
            return -1;
        };
}

Answer 8

Use:

function isInArray(array, search)
{
    return array.indexOf(search) >= 0;
}

// Usage
if(isInArray(my_array, "my_value"))
{
    //...
}

Answer 9

Extending the JavaScript Array object is a really bad idea because you introduce new properties (your custom methods) into for-in loops which can break existing scripts. A few years ago the authors of the Prototype library had to re-engineer their library implementation to remove just this kind of thing.

If you don't need to worry about compatibility with other JavaScript running on your page, go for it, otherwise, I'd recommend the more awkward, but safer free-standing function solution.

Answer 10

Performance

Today 2020.01.07 I perform tests on MacOs HighSierra 10.13.6 on Chrome v78.0.0, Safari v13.0.4 and Firefox v71.0.0 for 15 chosen solutions. Conclusions

• solutions based on JSON , Set and surprisingly find (K,N,O) are slowest on all browsers
• the es6 includes (F) is fast only on chrome
• the solutions based on for (C,D) and indexOf (G,H) are quite-fast on all browsers on small and big arrays so probably they are best choice for efficient solution
• the solutions where index decrease during loop, (B) is slower probably because the way of CPU cache works .
• I also run test for big array when searched element was on position 66% of array length, and solutions based on for (C,D,E) gives similar results (~630 ops/sec - but the E on safari and firefox was 10-20% slower than C and D)

Results

Details

I perform 2 tests cases: for array with 10 elements, and array with 1 milion elements. In both cases we put searched element in the array middle.

 let log = (name,f) => console.log(`${name}: 3-${f(arr,'s10')} 's7'-${f(arr,'s7')} 6-${f(arr,6)} 's3'-${f(arr,'s3')}`) let arr = [1,2,3,4,5,'s6','s7','s8','s9','s10']; //arr = new Array(1000000).fill(123); arr[500000]=7; function A(a, val) { var i = -1; var n = a.length; while (i++<n) { if (a[i] === val) { return true; } } return false; } function B(a, val) { var i = a.length; while (i--) { if (a[i] === val) { return true; } } return false; } function C(a, val) { for (var i = 0; i < a.length; i++) { if (a[i] === val) return true; } return false; } function D(a,val) { var len = a.length; for(var i = 0 ; i < len;i++) { if(a[i] === val) return true; } return false; } function E(a, val){ var n = a.length-1; var t = n/2; for (var i = 0; i <= t; i++) { if (a[i] === val || a[ni] === val) return true; } return false; } function F(a,val) { return a.includes(val); } function G(a,val) { return a.indexOf(val)>=0; } function H(a,val) { return !!~a.indexOf(val); } function I(a, val) { return a.findIndex(x=> x==val)>=0; } function J(a,val) { return a.some(x=> x===val); } function K(a, val) { const s = JSON.stringify(val); return a.some(x => JSON.stringify(x) === s); } function L(a,val) { return !a.every(x=> x!==val); } function M(a, val) { return !!a.find(x=> x==val); } function N(a,val) { return a.filter(x=>x===val).length > 0; } function O(a, val) { return new Set(a).has(val); } log('A',A); log('B',B); log('C',C); log('D',D); log('E',E); log('F',F); log('G',G); log('H',H); log('I',I); log('J',J); log('K',K); log('L',L); log('M',M); log('N',N); log('O',O);

 This shippet only presents functions used in performance tests - it not perform tests itself!

Array small - 10 elements

You can perform tests in your machine HERE

Array big - 1.000.000 elements

You can perform tests in your machine HERE

Answer 11

One-liner:

function contains(arr, x) {
    return arr.filter(function(elem) { return elem == x }).length > 0;
}

Answer 12

Thinking out of the box for a second, if you are making this call many many times, it is vastly more efficient to use an associative array a Map to do lookups using a hash function.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map

Answer 13

I use the following:

Array.prototype.contains = function (v) {
    return this.indexOf(v) > -1;
}

var a = [ 'foo', 'bar' ];

a.contains('foo'); // true
a.contains('fox'); // false

Answer 14

function contains(a, obj) {
    return a.some(function(element){return element == obj;})
}

Array.prototype.some() was added to the ECMA-262 standard in the 5th edition

Answer 15

If you are using JavaScript 1.6 or later (Firefox 1.5 or later) you can use Array.indexOf . Otherwise, I think you are going to end up with something similar to your original code.

Answer 16

A hopefully faster bidirectional indexOf / lastIndexOf alternative

2015

While the new method includes is very nice, the support is basically zero for now.

It's a long time that I was thinking of a way to replace the slow indexOf / lastIndexOf functions.

A performant way has already been found, looking at the top answers. From those I chose the contains function posted by @Damir Zekic which should be the fastest one. But it also states that the benchmarks are from 2008 and so are outdated.

I also prefer while over for , but for not a specific reason I ended writing the function with a for loop. It could be also done with a while -- .

I was curious if the iteration was much slower if I check both sides of the array while doing it. Apparently no, and so this function is around two times faster than the top voted ones. Obviously it's also faster than the native one. This is in a real world environment, where you never know if the value you are searching is at the beginning or at the end of the array.

When you know you just pushed an array with a value, using lastIndexOf remains probably the best solution, but if you have to travel through big arrays and the result could be everywhere, this could be a solid solution to make things faster.

Bidirectional indexOf / lastIndexOf

function bidirectionalIndexOf(a, b, c, d, e){
  for(c=a.length,d=c*1; c--; ){
    if(a[c]==b) return c; //or this[c]===b
    if(a[e=d-1-c]==b) return e; //or a[e=d-1-c]===b
  }
  return -1
}

//Usage
bidirectionalIndexOf(array,'value');

Performance test

https://jsbench.me/7el1b8dj80

As a test I created an array with 100k entries.

Three queries: at the beginning, in the middle & at the end of the array.

I hope you also find this interesting and test the performance.

Note: As you can see I slightly modified the contains function to reflect the indexOf & lastIndexOf output (so basically true with the index and false with -1 ). That shouldn't harm it.

The array prototype variant

Object.defineProperty(Array.prototype,'bidirectionalIndexOf',{value:function(b,c,d,e){
  for(c=this.length,d=c*1; c--; ){
    if(this[c]==b) return c; //or this[c]===b
    if(this[e=d-1-c] == b) return e; //or this[e=d-1-c]===b
  }
  return -1
},writable:false, enumerable:false});

// Usage
array.bidirectionalIndexOf('value');

The function can also be easily modified to return true or false or even the object, string or whatever it is.

And here is the while variant:

function bidirectionalIndexOf(a, b, c, d){
  c=a.length; d=c-1;
  while(c--){
    if(b===a[c]) return c;
    if(b===a[d-c]) return d-c;
  }
  return c
}

// Usage
bidirectionalIndexOf(array,'value');

How is this possible?

I think that the simple calculation to get the reflected index in an array is so simple that it's two times faster than doing an actual loop iteration.

Here is a complex example doing three checks per iteration, but this is only possible with a longer calculation which causes the slowdown of the code.

https://web.archive.org/web/20151019160219/http://jsperf.com/bidirectionalindexof/2

Answer 17

function inArray(elem,array)
{
    var len = array.length;
    for(var i = 0 ; i < len;i++)
    {
        if(array[i] == elem){return i;}
    }
    return -1;
} 

Returns array index if found, or -1 if not found

Answer 18

We use this snippet (works with objects, arrays, strings):

/*
 * @function
 * @name Object.prototype.inArray
 * @description Extend Object prototype within inArray function
 *
 * @param {mix}    needle       - Search-able needle
 * @param {bool}   searchInKey  - Search needle in keys?
 *
 */
Object.defineProperty(Object.prototype, 'inArray',{
    value: function(needle, searchInKey){

        var object = this;

        if( Object.prototype.toString.call(needle) === '[object Object]' || 
            Object.prototype.toString.call(needle) === '[object Array]'){
            needle = JSON.stringify(needle);
        }

        return Object.keys(object).some(function(key){

            var value = object[key];

            if( Object.prototype.toString.call(value) === '[object Object]' || 
                Object.prototype.toString.call(value) === '[object Array]'){
                value = JSON.stringify(value);
            }

            if(searchInKey){
                if(value === needle || key === needle){
                return true;
                }
            }else{
                if(value === needle){
                    return true;
                }
            }
        });
    },
    writable: true,
    configurable: true,
    enumerable: false
});

Usage:

var a = {one: "first", two: "second", foo: {three: "third"}};
a.inArray("first");          //true
a.inArray("foo");            //false
a.inArray("foo", true);      //true - search by keys
a.inArray({three: "third"}); //true

var b = ["one", "two", "three", "four", {foo: 'val'}];
b.inArray("one");         //true
b.inArray('foo');         //false
b.inArray({foo: 'val'})   //true
b.inArray("{foo: 'val'}") //false

var c = "String";
c.inArray("S");        //true
c.inArray("s");        //false
c.inArray("2", true);  //true
c.inArray("20", true); //false

Answer 19

If you are checking repeatedly for existence of an object in an array you should maybe look into

1. Keeping the array sorted at all times by doing insertion sort in your array (put new objects in on the right place)
2. Make updating objects as remove+sorted insert operation and
3. Use a binary search lookup in your contains(a, obj) .

Answer 20

Solution that works in all modern browsers:

function contains(arr, obj) {
  const stringifiedObj = JSON.stringify(obj); // Cache our object to not call `JSON.stringify` on every iteration
  return arr.some(item => JSON.stringify(item) === stringifiedObj);
}

Usage:

contains([{a: 1}, {a: 2}], {a: 1}); // true

IE6+ solution:

function contains(arr, obj) {
  var stringifiedObj = JSON.stringify(obj)
  return arr.some(function (item) {
    return JSON.stringify(item) === stringifiedObj;
  });
}

// .some polyfill, not needed for IE9+
if (!('some' in Array.prototype)) {
  Array.prototype.some = function (tester, that /*opt*/) {
    for (var i = 0, n = this.length; i < n; i++) {
      if (i in this && tester.call(that, this[i], i, this)) return true;
    } return false;
  };
}

Usage:

contains([{a: 1}, {a: 2}], {a: 1}); // true

Why to use JSON.stringify ?

Array.indexOf and Array.includes (as well as most of the answers here) only compare by reference and not by value.

[{a: 1}, {a: 2}].includes({a: 1});
// false, because {a: 1} is a new object

Bonus

Non-optimized ES6 one-liner:

[{a: 1}, {a: 2}].some(item => JSON.stringify(item) === JSON.stringify({a: 1));
// true

---

Note: Comparing objects by value will work better if the keys are in the same order, so to be safe you might sort the keys first with a package like this one: https://www.npmjs.com/package/sort-keys

---

Updated the contains function with a perf optimization. Thanks itinance for pointing it out.

Answer 21

Use lodash's some function.

It's concise, accurate and has great cross platform support.

The accepted answer does not even meet the requirements.

Requirements: Recommend most concise and efficient way to find out if a JavaScript array contains an object.

Accepted Answer:

$.inArray({'b': 2}, [{'a': 1}, {'b': 2}])
> -1

My recommendation:

_.some([{'a': 1}, {'b': 2}], {'b': 2})
> true

Notes:

$.inArray works fine for determining whether a scalar value exists in an array of scalars...

$.inArray(2, [1,2])
> 1

... but the question clearly asks for an efficient way to determine if an object is contained in an array.

In order to handle both scalars and objects, you could do this:

(_.isObject(item)) ? _.some(ary, item) : (_.indexOf(ary, item) > -1)

Answer 22

Simple solution for this requirement is using find()

If you're having array of objects like below,

var users = [{id: "101", name: "Choose one..."},
{id: "102", name: "shilpa"},
{id: "103", name: "anita"},
{id: "104", name: "admin"},
{id: "105", name: "user"}];

Then you can check whether the object with your value is already present or not:

let data = users.find(object => object['id'] === '104');

if data is null then no admin, else it will return the existing object like:

{id: "104", name: "admin"}

Then you can find the index of that object in the array and replace the object using the code:

let indexToUpdate = users.indexOf(data);
let newObject = {id: "104", name: "customer"};
users[indexToUpdate] = newObject;//your new object
console.log(users);

you will get value like:

[{id: "101", name: "Choose one..."},
{id: "102", name: "shilpa"},
{id: "103", name: "anita"},
{id: "104", name: "customer"},
{id: "105", name: "user"}];

Answer 23

While array.indexOf(x)!=-1 is the most concise way to do this (and has been supported by non-Internet Explorer browsers for over decade...), it is not O(1), but rather O(N), which is terrible. If your array will not be changing, you can convert your array to a hashtable, then do table[x]!==undefined or ===undefined :

Array.prototype.toTable = function() {
    var t = {};
    this.forEach(function(x){t[x]=true});
    return t;
}

Demo:

var toRemove = [2,4].toTable();
[1,2,3,4,5].filter(function(x){return toRemove[x]===undefined})

(Unfortunately, while you can create an Array.prototype.contains to "freeze" an array and store a hashtable in this._cache in two lines, this would give wrong results if you chose to edit your array later. JavaScript has insufficient hooks to let you keep this state, unlike Python for example.)

Answer 24

ECMAScript 6 has an elegant proposal on find.

The find method executes the callback function once for each element present in the array until it finds one where callback returns a true value. If such an element is found, find immediately returns the value of that element. Otherwise, find returns undefined. callback is invoked only for indexes of the array which have assigned values; it is not invoked for indexes which have been deleted or which have never been assigned values.

Here is the MDN documentation on that.

The find functionality works like this.

function isPrime(element, index, array) {
    var start = 2;
    while (start <= Math.sqrt(element)) {
        if (element % start++ < 1) return false;
    }
    return (element > 1);
}

console.log( [4, 6, 8, 12].find(isPrime) ); // Undefined, not found
console.log( [4, 5, 8, 12].find(isPrime) ); // 5

You can use this in ECMAScript 5 and below by defining the function .

if (!Array.prototype.find) {
  Object.defineProperty(Array.prototype, 'find', {
    enumerable: false,
    configurable: true,
    writable: true,
    value: function(predicate) {
      if (this == null) {
        throw new TypeError('Array.prototype.find called on null or undefined');
      }
      if (typeof predicate !== 'function') {
        throw new TypeError('predicate must be a function');
      }
      var list = Object(this);
      var length = list.length >>> 0;
      var thisArg = arguments[1];
      var value;

      for (var i = 0; i < length; i++) {
        if (i in list) {
          value = list[i];
          if (predicate.call(thisArg, value, i, list)) {
            return value;
          }
        }
      }
      return undefined;
    }
  });
}

Answer 25

One can use Set that has the method "has()":

 function contains(arr, obj) { var proxy = new Set(arr); if (proxy.has(obj)) return true; else return false; } var arr = ['Happy', 'New', 'Year']; console.log(contains(arr, 'Happy'));

Answer 26

Use:

var myArray = ['yellow', 'orange', 'red'] ;

alert(!!~myArray.indexOf('red')); //true

Demo

To know exactly what the tilde ~ do at this point, refer to this question What does a tilde do when it precedes an expression? .

Answer 27

OK, you can just optimise your code to get the result!

There are many ways to do this which are cleaner and better, but I just wanted to get your pattern and apply to that using JSON.stringify , just simply do something like this in your case:

function contains(a, obj) {
    for (var i = 0; i < a.length; i++) {
        if (JSON.stringify(a[i]) === JSON.stringify(obj)) {
            return true;
        }
    }
    return false;
}

Answer 28

Surprised that this question still doesn't have latest syntax added, adding my 2 cents.

Let's say we have array of Objects arrObj and we want to search obj in it.

Array.prototype. indexOf -> (returns index or -1 ) is generally used for finding index of element in array. This can also be used for searching object but only works if you are passing reference to same object.

let obj = { name: 'Sumer', age: 36 };
let arrObj = [obj, { name: 'Kishor', age: 46 }, { name: 'Rupen', age: 26 }];


console.log(arrObj.indexOf(obj));// 0
console.log(arrObj.indexOf({ name: 'Sumer', age: 36 })); //-1

console.log([1, 3, 5, 2].indexOf(2)); //3

Array.prototype. includes -> (returns true or false )

console.log(arrObj.includes(obj));  //true
console.log(arrObj.includes({ name: 'Sumer', age: 36 })); //false

console.log([1, 3, 5, 2].includes(2)); //true

Array.prototype. find -> (takes callback, returns first value/object that returns true in CB).

console.log(arrObj.find(e => e.age > 40));  //{ name: 'Kishor', age: 46 }
console.log(arrObj.find(e => e.age > 40)); //{ name: 'Kishor', age: 46 }

console.log([1, 3, 5, 2].find(e => e > 2)); //3

Array.prototype. findIndex -> (takes callback, returns index of first value/object that returns true in CB).

console.log(arrObj.findIndex(e => e.age > 40));  //1
console.log(arrObj.findIndex(e => e.age > 40)); //1

console.log([1, 3, 5, 2].findIndex(e => e > 2)); //1

Since find and findIndex takes a callback, we can be fetch any object(even if we don't have the reference) from array by creatively setting the true condition.

Answer 29

It has one parameter: an array numbers of objects. Each object in the array has two integer properties denoted by x and y. The function must return a count of all such objects in the array that satisfy numbers.x == numbers.y

 var numbers = [ { x: 1, y: 1 }, { x: 2, y: 3 }, { x: 3, y: 3 }, { x: 3, y: 4 }, { x: 4, y: 5 } ]; var count = 0; var n = numbers.length; for (var i =0;i<n;i++) { if(numbers[i].x==numbers[i].y) {count+=1;} } alert(count);

Answer 30

 function countArray(originalArray) { var compressed = []; // make a copy of the input array var copyArray = originalArray.slice(0); // first loop goes over every element for (var i = 0; i < originalArray.length; i++) { var count = 0; // loop over every element in the copy and see if it's the same for (var w = 0; w < copyArray.length; w++) { if (originalArray[i] == copyArray[w]) { // increase amount of times duplicate is found count++; // sets item to undefined delete copyArray[w]; } } if (count > 0) { var a = new Object(); a.value = originalArray[i]; a.count = count; compressed.push(a); } } return compressed; }; // It should go something like this: var testArray = new Array("dog", "dog", "cat", "buffalo", "wolf", "cat", "tiger", "cat"); var newArray = countArray(testArray); console.log(newArray);

Answer 31

use Array.prototype.includes for example:

 const fruits = ['coconut', 'banana', 'apple'] const doesFruitsHaveCoconut = fruits.includes('coconut')// true console.log(doesFruitsHaveCoconut)

maybe read this documentation from MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/includes

Answer 32

Here's how Prototype does it :

/**
 *  Array#indexOf(item[, offset = 0]) -> Number
 *  - item (?): A value that may or may not be in the array.
 *  - offset (Number): The number of initial items to skip before beginning the
 *      search.
 *
 *  Returns the position of the first occurrence of `item` within the array — or
 *  `-1` if `item` doesn't exist in the array.
**/
function indexOf(item, i) {
  i || (i = 0);
  var length = this.length;
  if (i < 0) i = length + i;
  for (; i < length; i++)
    if (this[i] === item) return i;
  return -1;
}

Also see here for how they hook it up.

Answer 33

By no means the best, but I was just getting creative and adding to the repertoire.

Do not use this

 Object.defineProperty(Array.prototype, 'exists', { value: function(element, index) { var index = index || 0 return index === this.length ? -1 : this[index] === element ? index : this.exists(element, ++index) } }) // Outputs 1 console.log(['one', 'two'].exists('two')); // Outputs -1 console.log(['one', 'two'].exists('three')); console.log(['one', 'two', 'three', 'four'].exists('four'));

Answer 34

1. Either use Array.indexOf(Object) .
2. With ECMA 7 one can use the Array.includes(Object) .

3. With ECMA 6 you can use Array.find(FunctionName) where FunctionName is a user defined function to search for the object in the array.

   Hope this helps!

Answer 35

Use indexOf()

You can use the indexOf() method to check whether a given value or element exists in an array or not. The indexOf() method returns the index of the element inside the array if it is found, and returns -1 if it not found. Let's take a look at the following example:

 var fruits = ["Apple", "Banana", "Mango", "Orange", "Papaya"]; var a = "Mango"; checkArray(a, fruits); function checkArray(a, fruits) { // Check if a value exists in the fruits array if (fruits.indexOf(a) !== -1) { return document.write("true"); } else { return document.write("false"); } }

Use include() Method

ES6 has introduced the includes() method to perform this task very easily. But, this method returns only true or false instead of index number:

 var fruits = ["Apple", "Banana", "Mango", "Orange", "Papaya"]; alert(fruits.includes("Banana")); // Outputs: true alert(fruits.includes("Coconut")); // Outputs: false alert(fruits.includes("Orange")); // Outputs: true alert(fruits.includes("Cherry")); // Outputs: false

For further reference checkout here

Answer 36

There are a couple of method which makes this easy to achieve ( includes , some , find , findIndex )

 const array = [1, 2, 3, 4, 5, 6, 7]; console.log(array.includes(3)); //includes() determines whether an array includes a certain value among its entries console.log(array.some(x => x === 3)); //some() tests if at least one element in the array passes the test implemented by the provided function console.log(array.find(x => x === 3) ? true : false); //find() returns the value of the first element in the provided array that satisfies the provided testing function console.log(array.findIndex(x => x === 3) > -1); //findIndex() returns the index of the first element in the array that satisfies the provided testing function, else returning -1.

Answer 37

You can also use this trick:

var arrayContains = function(object) {
  return (serverList.filter(function(currentObject) {
    if (currentObject === object) {
      return currentObject
    }
    else {
      return false;
    }
  }).length > 0) ? true : false
}

Answer 38

As others have mentioned you can use Array.indexOf , but it isn't available in all browsers. Here's the code from https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Array/indexOf to make it work the same in older browsers.

indexOf is a recent addition to the ECMA-262 standard; as such it may not be present in all browsers. You can work around this by inserting the following code at the beginning of your scripts, allowing use of indexOf in implementations which do not natively support it. This algorithm is exactly the one specified in ECMA-262, 5th edition, assuming Object, TypeError, Number, Math.floor, Math.abs, and Math.max have their original value.

if (!Array.prototype.indexOf) {
    Array.prototype.indexOf = function (searchElement /*, fromIndex */ ) {
        "use strict";
        if (this == null) {
            throw new TypeError();
        }
        var t = Object(this);
        var len = t.length >>> 0;
        if (len === 0) {
            return -1;
        }
        var n = 0;
        if (arguments.length > 1) {
            n = Number(arguments[1]);
            if (n != n) { // shortcut for verifying if it's NaN
                n = 0;
            } else if (n != 0 && n != Infinity && n != -Infinity) {
                n = (n > 0 || -1) * Math.floor(Math.abs(n));
            }
        }
        if (n >= len) {
            return -1;
        }
        var k = n >= 0 ? n : Math.max(len - Math.abs(n), 0);
        for (; k < len; k++) {
            if (k in t && t[k] === searchElement) {
                return k;
            }
        }
        return -1;
    }
}

Answer 39

Or this solution:

Array.prototype.includes = function (object) {
  return !!+~this.indexOf(object);
};

Answer 40

Using idnexOf() it is a good solution, but you should hide embedded implementation indexOf() function which returns -1 with ~ operator:

function include(arr,obj) { 
    return !!(~arr.indexOf(obj)); 
} 

Answer 41

I was working on a project that I needed a functionality like python set which removes all duplicates values and returns a new list, so I wrote this function maybe useful to someone

function set(arr) {
    var res = [];
    for (var i = 0; i < arr.length; i++) {
        if (res.indexOf(arr[i]) === -1) {
            res.push(arr[i]);
        }
    }
    return res;
}

Answer 42

If you're working with ES6 You can use a set:

function arrayHas( array, element ) {
    const s = new Set(array);
    return s.has(element)
}

This should be more performant than just about any other method

Answer 43

I recommended to use underscore library because its return the value and its supported for all browsers.

underscorejs

 var findValue = _.find(array, function(item) {
    return item.id == obj.id;
 });

Answer 44

In Addition to what others said, if you don't have a reference of the object which you want to search in the array, then you can do something like this.

let array = [1, 2, 3, 4, {"key": "value"}];

array.some((element) => JSON.stringify(element) === JSON.stringify({"key": "value"})) // true

array.some((element) => JSON.stringify(element) === JSON.stringify({})) // true

Array.some returns true if any element matches the given condition and returns false if none of the elements matches the given condition.

Answer 45

Object.keys for getting all property names of the object and filter all values that exact or partial match with specified string.

 function filterByValue(array, string) { return array.filter(o => Object.keys(o).some(k => o[k].toLowerCase().includes(string.toLowerCase()))); } const arrayOfObject = [{ name: 'Paul', country: 'Canada', }, { name: 'Lea', country: 'Italy', }, { name: 'John', country: 'Italy' }]; console.log(filterByValue(arrayOfObject, 'lea')); // [{name: 'Lea', country: 'Italy'}] console.log(filterByValue(arrayOfObject, 'ita')); // [{name: 'Lea', country: 'Italy'}, {name: 'John', country: 'Italy'}]

You can also filter by specific key such as.

Object.keys(o).some(k => o.country.toLowerCase().includes(string.toLowerCase())));

Now you can just check array count after filtered to check value contains or not.

Hope it's helpful.

Answer 46

Adding a unique item to a another list

searchResults: [
                {
                    name: 'Hello',
                    artist: 'Selana',
                    album: 'Riga',
                    id: 1,
                },
                {
                    name: 'Hello;s',
                    artist: 'Selana G',
                    album: 'Riga1',
                    id: 2,
                },
                {
                    name: 'Hello2',
                    artist: 'Selana',
                    album: 'Riga11',
                    id: 3,
                }
            ],
            playlistTracks: [
              {
                name: 'Hello',
                artist: 'Mamunuus',
                album: 'Riga',
                id: 4,
              },
              {
                name: 'Hello;s',
                artist: 'Mamunuus G',
                album: 'Riga1',
                id: 2,
              },
              {
                name: 'Hello2',
                artist: 'Mamunuus New',
                album: 'Riga11',
                id: 3,
              }
            ],
            playlistName: "New PlayListTrack",
        };
    }

    // Adding an unique track in the playList
    addTrack = track => {
      if(playlistTracks.find(savedTrack => savedTrack.id === track.id)) {
        return;
      }
      playlistTracks.push(track);

      this.setState({
        playlistTracks
      })
    };

Answer 47

This may be a detailed and easy solution.

//plain array
var arr = ['a', 'b', 'c'];
var check = arr.includes('a');
console.log(check); //returns true
if (check)
{
   // value exists in array
   //write some codes
}

// array with objects
var arr = [
      {x:'a', y:'b'},
      {x:'p', y:'q'}
  ];

// if you want to check if x:'p' exists in arr
var check = arr.filter(function (elm){
    if (elm.x == 'p')
    {
       return elm; // returns length = 1 (object exists in array)
    }
});

// or y:'q' exists in arr
var check = arr.filter(function (elm){
    if (elm.y == 'q')
    {
       return elm; // returns length = 1 (object exists in array)
    }
});

// if you want to check, if the entire object {x:'p', y:'q'} exists in arr
var check = arr.filter(function (elm){
    if (elm.x == 'p' && elm.y == 'q')
    {
       return elm; // returns length = 1 (object exists in array)
    }
});

// in all cases
console.log(check.length); // returns 1

if (check.length > 0)
{
   // returns true
   // object exists in array
   //write some codes
}

Answer 48

The best default method to check if value exist in array JavaScript is some()

Array.prototype.some()

The some() method tests whether at least one element in the array passes the test implemented by the provided function. It returns true if, in the array, it finds an element for which the provided function returns true; otherwise it returns false. It doesn't modify the array.

const array = [1, 2, 3, 4, 5];

// checks whether an element is even
const even = (element) => element % 2 === 0;

console.log(array.some(even));
// expected output: true

The some method is the best one in Browser compatibility

For more documentation Array.prototype.some() - JavaScript | MDN

Also you can use other two method is find() and includes() . with those method you can get your result but not the best one.

Array.prototype.find() - JavaScript | MDN

Array.prototype.includes() - JavaScript | MDN

Answer 49

Use:

Array.prototype.contains = function(x){
  var retVal = -1;

  // x is a primitive type
  if(["string","number"].indexOf(typeof x)>=0 ){ retVal = this.indexOf(x);}

  // x is a function
  else if(typeof x =="function") for(var ix in this){
    if((this[ix]+"")==(x+"")) retVal = ix;
  }

  //x is an object...
  else {
    var sx=JSON.stringify(x);
    for(var ix in this){
      if(typeof this[ix] =="object" && JSON.stringify(this[ix])==sx) retVal = ix;
    }
  }

  //Return False if -1 else number if numeric otherwise string
  return (retVal === -1)?false : ( isNaN(+retVal) ? retVal : +retVal);
}

I know it's not the best way to go, but since there is no native IComparable way to interact between objects, I guess this is as close as you can get to compare two entities in an array. Also, extending Array object might not be a wise thing to do, but sometimes it's OK (if you are aware of it and the trade-off).

Answer 50

I looked through submitted answers and got that they only apply if you search for the object via reference. A simple linear search with reference object comparison.

But lets say you don't have the reference to an object, how will you find the correct object in the array? You will have to go linearly and deep compare with each object. Imagine if the list is too large, and the objects in it are very big containing big pieces of text. The performance drops drastically with the number and size of the elements in the array.

You can stringify objects and put them in the native hash table, but then you will have data redundancy remembering these keys cause JavaScript keeps them for 'for i in obj', and you only want to check if the object exists or not, that is, you have the key.

I thought about this for some time constructing a JSON Schema validator, and I devised a simple wrapper for the native hash table, similar to the sole hash table implementation, with some optimization exceptions which I left to the native hash table to deal with. It only needs performance benchmarking... All the details and code can be found on my blog: http://stamat.wordpress.com/javascript-quickly-find-very-large-objects-in-a-large-array/ I will soon post benchmark results.

The complete solution works like this:

var a = {'a':1,
 'b':{'c':[1,2,[3,45],4,5],
 'd':{'q':1, 'b':{'q':1, 'b':8},'c':4},
 'u':'lol'},
 'e':2};

 var b = {'a':1, 
 'b':{'c':[2,3,[1]],
 'd':{'q':3,'b':{'b':3}}},
 'e':2};

 var c = "Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.";

 var hc = new HashCache([{a:3, b:2, c:5}, {a:15, b:2, c:'foo'}]); //init

 hc.put({a:1, b:1});
 hc.put({b:1, a:1});
 hc.put(true);
 hc.put('true');
 hc.put(a);
 hc.put(c);
 hc.put(d);
 console.log(hc.exists('true'));
 console.log(hc.exists(a));
 console.log(hc.exists(c));
 console.log(hc.exists({b:1, a:1}));
 hc.remove(a);
 console.log(hc.exists(c));

Answer 51

Similar thing: Finds the first element by a "search lambda":

Array.prototype.find = function(search_lambda) {
  return this[this.map(search_lambda).indexOf(true)];
};

Usage:

[1,3,4,5,8,3,5].find(function(item) { return item % 2 == 0 })
=> 4

Same in coffeescript:

Array.prototype.find = (search_lambda) -> @[@map(search_lambda).indexOf(true)]

Answer 52

Simple solution : ES6 Features " includes " method

let arr = [1, 2, 3, 2, 3, 2, 3, 4];

  arr.includes(2) // true

  arr.includes(93) // false

Answer 53

There are several ways to find out. You can use inbuilt Array methods. The most prominently used is Array find method.

const arr1 = [1, 2, 3, 4, 5]
const result = arr1.find(ele => ele === 4)
console.log(result) //4

const result2 = arr1.find(ele => ele === 6)
console.log(result2) //undefined
/* 
If the element is present inside the array
then it will return the first element that
satisfies the given condition. Otherwise
undefined will return.
*/

Answer 54

You can use findIndex function to check if an array has a specific value.

arrObj.findIndex(obj => obj === comparedValue) !== -1;

Returns true if arrObj contains comparedValue, false otherwise.

Answer 55

使用正则表达式：

console.log(new RegExp('26242').test(['23525', '26242', '25272'].join(''))) // true

Answer 56

If you're just trying to check whether a value is included in a collection, It would be more appropriate to use a Set , As Arrays can have duplicate values whereas Sets cannot. Also, Replacing array.includes with set.has improves the performance from O(n ² ) to O(n). This will be useful when you have to look up multiple values for the same Set. so if you're just going to look up a single value, there's no benefit to use set.has , you can just use an array.includes .

Created a jsbench demo, You can run this to check the performance.

Screenshot of the test execution :

Answer 57

The fastest method in Javascript to find if an array contains a value is this:

function existsInArrayForIgnoreDataType(arr, targetElem) {
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] == targetElem) return true
  }
  return false
 }

You can find the complete study I did here .

Answer 58

let isExistOrNot = (arr, element)=>{
    return arr.includes(element);
    // includes check that an element is included or not in an array
    // it return a boolean value true or false
}

let array = ['apple', 'ball', 'cat', 'dog']

console.log(isExistOrNot(array, 'yellow'));
//Result false because yellow doesn't exist in array
console.log(isExistOrNot(array, 'apple'));
//Result true because yellow exist in array

Answer 59

Literally:

(using Firefox v3.6, with for-in caveats as previously noted (HOWEVER the use below might endorse for-in for this very purpose! That is, enumerating array elements that ACTUALLY exist via a property index (HOWEVER, in particular, the array length property is NOT enumerated in the for-in property list!).).)

(Drag & drop the following complete URI's for immediate mode browser testing.)

JavaScript:

  function ObjInRA(ra){var has=false; for(i in ra){has=true; break;} return has;}

  function check(ra){
      return ['There is ',ObjInRA(ra)?'an':'NO',' object in [',ra,'].'].join('')
  }
  alert([
            check([{}]), check([]), check([,2,3]),
            check(['']), '\t (a null string)', check([,,,])
        ].join('\n'));

which displays:

There is an object in [[object Object]].
There is NO object in [].
There is an object in [,2,3].
There is an object in [].
     (a null string)
There is NO object in [,,].

Wrinkles: if looking for a "specific" object consider:

JavaScript: alert({}!={}); alert({}!=={}); alert({}!={}); alert({}!=={});

And thus:

JavaScript:

 obj = {prop:"value"}; 
 ra1 = [obj]; 
 ra2 = [{prop:"value"}];
 alert(ra1[0] == obj); 
 alert(ra2[0] == obj);

Often ra2 is considered to "contain" obj as the literal entity {prop:"value"} .

A very coarse, rudimentary, naive (as in code needs qualification enhancing) solution:

JavaScript:

  obj={prop:"value"};   ra2=[{prop:"value"}];
  alert(
    ra2 . toSource() . indexOf( obj.toSource().match(/^.(.*).$/)[1] ) != -1 ?
      'found' :
      'missing' );

See ref: Searching for objects in JavaScript arrays .

Answer 60

Just another option

// usage: if ( ['a','b','c','d'].contains('b') ) { ... }
Array.prototype.contains = function(value){
    for (var key in this)
        if (this[key] === value) return true;
    return false;
}

Be careful because overloading javascript array objects with custom methods can disrupt the behavior of other javascripts, causing unexpected behavior.