flatten.js

var arr = [[1,2,[3]],4,[5,[6.2]]];
var result = [];

function flattenWithMap(array) {
	//Convert the array to a flat string, split it using commas, and map it using 
	//the "Number" function to convert each element back to Integer :)
	if(array.constructor === Array)
		return array.toString().split(',').map(Number);
	else
		return array;
}

function flattenRecursive(elem, res) {
	if(elem.constructor === Array) //Checks if the element passed as the first parameter
		for(var i = 0; i < elem.length; i++) //traverses the array and looks for any nested arrays
			flattenRecursive(elem[i], res); //the second parameter that holds the result is passed along recursively
	else
		res.push(elem);// Pushes the integer into the result array
	return res; //returns the result array back up
}

console.log(flattenWithMap(arr));
console.log(flattenRecursive(arr, result));

//Code is a short essay (usually) written to the computer, which in turn reads it as an Ode, if done right ;)