Basic Object.keys polyfill

Object.keys-polyfill.js

; (function () {

	if (!Object.keys) {

		Object.keys = function (o) {

			if (o !== Object(o)) {
				throw new TypeError('Object.keys called on a non-object');
			}

			var k = [],
				p;

			for (p in o) {

				// Use direct access, just in case this object has overridden the hasOwnProperty method which does something different.
				// Also as it wont go through the prototype chain to find the method, it should be quicker
				// Finally hasOwnProperty is set on the lowest level prototype 'Object' which all object derive from. However Object.create(null) can be used to
				// create an object that has no base prototype, meaning hasOwnProperty would not exist (however this usage of Object.create is not recommended)
				if (Object.prototype.hasOwnProperty.call(o, p)) {
					k.push(p);
				}
			}

			return k;
		}
	}

})();