How to efficiently count the number of keys/properties of an object in JavaScript

Question

What's the fastest way to count the number of keys/properties of an object? Is it possible to do this without iterating over the object? I.e., without doing:

var count = 0; for (k in myobj) if (myobj.hasOwnProperty(k)) ++count; 

(Firefox did provide a magic __count__ property, but this was removed somewhere around version 4.)

Answer 1

To do this in any ES5-compatible environment, such as Node.js, Chrome, Internet Explorer 9+, Firefox 4+, or Safari 5+:

Object.keys(obj).length 

• Browser compatibility
• Object.keys documentation (includes a method you can add to non-ES5 browsers)

Answer 2

You could use this code:

if (!Object.keys) {     Object.keys = function (obj) {         var keys = [],             k;         for (k in obj) {             if (Object.prototype.hasOwnProperty.call(obj, k)) {                 keys.push(k);             }         }         return keys;     }; } 

Then you can use this in older browsers as well:

var len = Object.keys(obj).length;