flatten.js

function flatten(arr) {
	var result = [];
	// iterate through array
	for(var i = 0; i < arr.length; i++) {
		// check if number or array
		if(typeof arr[i] === "object") {
			// push values of array recursively 
			Array.prototype.push.apply(result, flatten(arr[i]));
		} else if (typeof arr[i] === "number") {
			// push number to end of array
			result.push(arr[i]);
		}
	}
	return result;
}