如何检查object是否在JavaScript中有任何属性？

Question

Assuming I declare

var ad = {}; 

How can I check whether this object will contain any user-defined properties?

Answer 1

You can use the built in Object.keys method to get a list of keys on an object and test its length.

var x = {};
// some code where value of x changes and than you want to check whether it is null or some object with values

if(Object.keys(x).length){
 // Your code here if x has some properties  
}

Answer 2

What about making a simple function?

function isEmptyObject(obj) {
  for(var prop in obj) {
    if (Object.prototype.hasOwnProperty.call(obj, prop)) {
      return false;
    }
  }
  return true;
}

isEmptyObject({}); // true
isEmptyObject({foo:'bar'});  // false

The hasOwnProperty method call directly on the Object.prototype is only to add little more safety , imagine the following using a normal obj.hasOwnProperty(...) call:

isEmptyObject({hasOwnProperty:'boom'});  // false

---

Note: _{(for the future)} The above method relies on the for...in statement, and this statement iterates only over enumerable properties, in the currently most widely implemented ECMAScript Standard (3rd edition) the programmer doesn't have any way to create non-enumerable properties.

However this has changed now with ECMAScript 5th Edition , and we are able to create non-enumerable, non-writable or non-deletable properties, so the above method can fail , eg:

var obj = {};
Object.defineProperty(obj, 'test', { value: 'testVal', 
  enumerable: false,
  writable: true,
  configurable: true
});
isEmptyObject(obj); // true, wrong!!
obj.hasOwnProperty('test'); // true, the property exist!!

An ECMAScript 5 solution to this problem would be:

function isEmptyObject(obj) {
  return Object.getOwnPropertyNames(obj).length === 0;
}

The Object.getOwnPropertyNames method returns an Array containing the names of all the own properties of an object, enumerable or not , this method is being implemented now by browser vendors, it's already on the Chrome 5 Beta and the latest WebKit Nightly Builds.

Object.defineProperty is also available on those browsers and latest Firefox 3.7 Alpha releases.

Answer 3

You can loop over the properties of your object as follows:

for(var prop in ad) {
    if (ad.hasOwnProperty(prop)) {
        // handle prop as required
    }
}

It is important to use the hasOwnProperty() method, to determine whether the object has the specified property as a direct property, and not inherited from the object's prototype chain.

Edit

From the comments: You can put that code in a function, and make it return false as soon as it reaches the part where there is the comment

Answer 4

With jQuery you can use:

$.isEmptyObject(obj); // Returns: Boolean

As of jQuery 1.4 this method checks both properties on the object itself and properties inherited from prototypes (in that it doesn't use hasOwnProperty).

With ECMAScript 5th Edition in modern browsers (IE9+, FF4+, Chrome5+, Opera12+, Safari5+) you can use the built in Object.keys method:

var obj = { blah: 1 };
var isEmpty = !Object.keys(obj).length;

Or plain old JavaScript:

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

Answer 5

Most recent browsers (and node.js) support Object.keys() which returns an array with all the keys in your object literal so you could do the following:

var ad = {}; 
Object.keys(ad).length;//this will be 0 in this case

Browser Support: Firefox 4, Chrome 5, Internet Explorer 9, Opera 12, Safari 5

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

Answer 6

If you're using underscore.js then you can use the _.isEmpty function:

var obj = {};
var emptyObject = _.isEmpty(obj);

Answer 7

If you are willing to use lodash , you can use the some method.

_.some(obj) // returns true or false

See this small jsbin example

Answer 8

for (var hasProperties in ad) break;
if (hasProperties)
    ... // ad has properties

If you have to be safe and check for Object prototypes (these are added by certain libraries and not there by default):

var hasProperties = false;
for (var x in ad) {
    if (ad.hasOwnProperty(x)) {
        hasProperties = true;
        break;
    }
}
if (hasProperties)
    ... // ad has properties

Answer 9

for(var memberName in ad)
{
  //Member Name: memberName
  //Member Value: ad[memberName]
}

Member means Member property, member variable, whatever you want to call it >_>

The above code will return EVERYTHING, including toString... If you only want to see if the object's prototype has been extended:

var dummyObj = {};  
for(var memberName in ad)
{
  if(typeof(dummyObj[memberName]) == typeof(ad[memberName])) continue; //note A
  //Member Name: memberName
  //Member Value: ad[memberName]

}

Note A: We check to see if the dummy object's member has the same type as our testing object's member. If it is an extend, dummyobject's member type should be "undefined"

Answer 10

var hasAnyProps = false; for (var key in obj) { hasAnyProps = true; break; }
// as of this line hasAnyProps will show Boolean whether or not any iterable props exist

Simple, works in every browser, and even though it's technically a loop for all keys on the object it does NOT loop through them all...either there's 0 and the loop doesn't run or there is some and it breaks after the first one (because all we're checking is if there's ANY...so why continue?)

Answer 11

ES6 function

/**
 * Returns true if an object is empty.
 * @param  {*} obj the object to test
 * @return {boolean} returns true if object is empty, otherwise returns false
 */
const pureObjectIsEmpty = obj => obj && obj.constructor === Object && Object.keys(obj).length === 0

Examples:

let obj = "this is an object with String constructor"
console.log(pureObjectIsEmpty(obj)) // empty? true

obj = {}
console.log(pureObjectIsEmpty(obj)) // empty? true

obj = []
console.log(pureObjectIsEmpty(obj)) // empty? true

obj = [{prop:"value"}]
console.log(pureObjectIsEmpty(obj)) // empty? true

obj = {prop:"value"}
console.log(pureObjectIsEmpty(obj)) // empty? false

Answer 12

Very late answer, but this is how you could handle it with prototypes.

Array.prototype.Any = function(func) {
    return this.some(func || function(x) { return x });
}

Object.prototype.IsAny = function() {
    return Object.keys(this).Any();
}

Answer 13

Late answer, but some frameworks handle objects as enumerables. Therefore, bob.js can do it like this:

var objToTest = {};
var propertyCount = bob.collections.extend(objToTest).count();

Answer 14

You can use the following:

Double bang !! property lookup

var a = !![]; // true
var a = !!null; // false

hasOwnProperty This is something that I used to use:

var myObject = {
  name: 'John',
  address: null
};
if (myObject.hasOwnProperty('address')) { // true
  // do something if it exists.
}

However, JavaScript decided not to protect the method's name, so it could be tampered with.

var myObject = {
  hasOwnProperty: 'I will populate it myself!'
};

prop in myObject

var myObject = {
  name: 'John',
  address: null,
  developer: false
};
'developer' in myObject; // true, remember it's looking for exists, not value.

typeof

if (typeof myObject.name !== 'undefined') {
  // do something
}

However, it doesn't check for null.

I think this is the best way.

in operator

var myObject = {
  name: 'John',
  address: null
};

if('name' in myObject) {
  console.log("Name exists in myObject");
}else{
  console.log("Name does not exist in myObject");
}

result:

Name exists in myObject

Here is a link that goes into more detail on the in operator: Determining if an object property exists

Answer 15

Object.hasOwn is a new static method (not fully supported by all browsers yet) which checks if the specified object has the indicated property as his own property and return true if that is the case. It will return false if the property is either inherited or does not exist on that object.

You can iterate through the object properties and check if they are indeed own properties

for (let property in ad) {
   if (Object.hasOwn(ad, property)) {
    // handle your code for object own properties here
  }
}   

More about Object.hasOwn - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/

Browser compatibility here - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/hasOwn#browser_compatibility

Answer 16

I'm not sure if this is a good approach but I use this condition to check if an object has or hasn't any property. Could be easily transformed into a function.

const obj = {};
    
if(function(){for (key in obj){return true}return false}())
{
  //do something;
}
else
{
  //do something else;
}
    
//Condition could be shorted by e.g. function(){for(key in obj){return 1}return 0}()

Answer 17

When sure that the object is a user-defined one, the easiest way to determine if UDO is empty, would be the following code:

isEmpty=
/*b.b Troy III p.a.e*/
function(x,p){for(p in x)return!1;return!0};

Even though this method is (by nature) a deductive one, - it's the quickest, and fastest possible.

a={};
isEmpty(a) >> true

a.b=1
isEmpty(a) >> false 

ps: !don't use it on browser-defined objects.

Answer 18

How about this?

var obj = {},
var isEmpty = !obj;
var hasContent = !!obj