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

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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.)

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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)

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