How to efficiently count the number of keys/properties of an object in JavaScript
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)
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;
If you are using Underscore.js you can use _.size (thanks douwe):
_.size(obj)Alternatively you can also use _.keys which might be clearer for some:
_.keys(obj).lengthI highly recommend Underscore.js. It's a tight library for doing lots of basic things. Whenever possible, they match ECMAScript 5 and defer to the native implementation.
Otherwise I support Avi Flax' answer. I edited it to add a link to the MDC documentation which includes the keys() method you can add to non-ECMAScript 5 browsers.