How to get object length [duplicate]

Question

Is there any built-in function that can return the length of an object?

For example, I have a = { 'a':1,'b':2,'c':3 } which should return 3. If I use a.length it returns undefined.

It could be a simple loop function, but I'd like to know if there's a built-in function?

There is a related question (Length of a JSON object) - in the chosen answer the user advises to transform object into an array, which is not pretty comfortable for my task.

Answer 1

For browsers supporting Object.keys() you can simply do:

Object.keys(a).length; 

Otherwise (notably in IE < 9), you can loop through the object yourself with a for (x in y) loop:

var count = 0; var i;  for (i in a) {     if (a.hasOwnProperty(i)) {         count++;     } } 

The hasOwnProperty is there to make sure that you're only counting properties from the object literal, and not properties it "inherits" from its prototype.