Flatten an Arbitrarily Nested Array

flatten.js

/**
* @function flattenNestedArray
* @description Flattens an arbitrarily nested array
* @param {Array} arrayToFlatten The array to flatten
* @return {Array}
*/
function flattenNestedArray(arrayToFlatten){
  var flattenedArray = [];
  arrayToFlatten.forEach(function(item) {
    if(Array.isArray(item)) {
      flattenedArray = flattenedArray.concat(flattenNestedArray(item));
    } else {
      flattenedArray.push(item);
    }
  });
  return flattenedArray;
}

// TEST CODE
var nestedArray = [[1,2,[3,[4,5]]],6];
var testArray = flattenNestedArray(nestedArray);
console.log(testArray);