Polyfill for the Object.assign method using only ES5 (broadly supported) features. Follows the spec exactly (http://www.ecma-international.org/ecma-262/7.0/#sec-object.assign)

Object-assign.js

// Documentation: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign
// Public domain

if (typeof Object.assign !== 'function') {
	Object.defineProperty(Object, 'assign', {
		configurable: true,
		enumerable: false,
		writable: true,

		// Second argument forces the `length` property to be 2, as per the spec
		value: function assign(target, sources) {
			if (typeof target === 'undefined')
				throw new TypeError("undefined cannot be converted to Object");
			else if (target === null)
				throw new TypeError("null cannot be converted to Object");
			else
				target = Object(target);

			for (var i = 1; i < arguments.length; ++i) {
				var nextSource = Object(arguments[i]);
				for (var key in nextSource)
					if (nextSource.hasOwnProperty(key))
						target[key] = nextSource[key];
			}
			
			return target;
		}
	});
}