Get all keys of a JavaScript object

Question

I was wondering if there was a quick way to extract keys of associative array into an array, or comma-separated list using JavaScript (jQuery is ok).

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Answer 1

Most of the major browsers have this functionality built-in now, the method is Object.keys():

var keys = Object.keys(options);
//-> ["key1", "key2"]

You can also use a little snippet to implement this in browsers that don't support it:

Object.keys = Object.keys || (function () {
    var hasOwnProperty = Object.prototype.hasOwnProperty;

    return function (o) {
        if (typeof o != "object" && typeof o != "function" || o === null)
            throw new TypeError("Object.keys called on a non-object");

        var result = [];
        for (var name in o) {
            if (hasOwnProperty.call(o, name))
                result.push(name);
        }

        return result;
    };
})();

That snippet works much the same as the one in Nick Craver's example with 2 exceptions:

• It will throw a meaningful TypeError if you pass anything other than an Object in (or "associative array", if you like).
• It will work around an annoying DOM-related issue in Internet Explorer where collections don't have the hasOwnProperty method.

This (and the other answers here) doesn't work around an IE enumeration bug, however. You can find more information and a partial work around for that on this answer here.