ES6 array Flatten to ES5 (reduce)

gistfile1.js

Array.prototype.flatten = Array.prototype.flatten || function() {
	var flattened = [];

	for (var i = 0; i < this.length; ++i) {
		if (Array.isArray(this[i])) {
			flattened = flattened.concat(this[i].flatten());
		} else {
			flattened.push(this[i]);
		}
	}

	return flattened;
};