flatten.js

		/**
		* The following flatten method is added to the Array prototype.
		* The method can directly be called on the Array object and will flatten it.
		* The contents of this file can be copy pasted into a browser window console and run.
		*/
		
		Array.prototype.flatten = function () {
			var array = this;
			var flatArray = this.flatArray || [];

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

			return flatArray;
		};

    //test sample
		var array = [[1, 2, [3]], 4];
		var newArray = array.flatten();
		console.log(newArray);