How to check if object has any properties in JavaScript?

Question

Assuming I declare

var ad = {}; 

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

Answer 1

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 2

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 3

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 4

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

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