JS Array flatten

flatten.js

'use strict';

/** Function to flatten sub-arrays within an array into one big array.
 * @param {Array} origArray - The array to flatten.
 *
 * @returns {Array} The flattened array.
 */
function flatten(origArray) {
	var flattenedArray = [];

	// Only do flatten operations if we're working on an array.
	if (Array.isArray(origArray)) {
		origArray.forEach(function (element) {
			// Flattened element if its is a sub-array.
			var flattenedSubArray = [];

			// If the element is an array, recursively flatten it.
			if (Array.isArray(element)) {
				flattenedSubArray = flatten(element).map(function (subElement) {
					return subElement;
				});
			// Otherwise, simply get the scalar element.
			} else {
				flattenedSubArray = [element];
			}

			// Finally, take the flattened sub-array here in the tail of the
			// recursion and push it to the final closed flattened array.
			flattenedSubArray.forEach(function (element) {
				flattenedArray.push(element);
			});
		});
	}

	return flattenedArray;
}

// Tests
// console.log([]);
// console.log(flatten([])); // -> []

// console.log([1,2,3,4]);
// console.log(flatten([1,2,3,4])); // -> [ 1, 2, 3, 4 ]

// console.log([1,2,{simpleNestedObject:true},4]);
// console.log(flatten([1,2,{simpleNestedObject:true},4])); // -> [ 1, 2, { simpleNestedObject: true }, 4 ]

// console.log([1,2,3,[4,5,6,7],8]);
// console.log(flatten([1,2,3,[4,5,6,7],8])); // -> [ 1, 2, 3, 4, 5, 6, 7, 8 ]

// console.log([1,2,3,[4,5,6,7,[8,9]],10]);
// console.log(flatten([1,2,[4,5,6,7,[8,9]],10])); // -> [ 1, 2, 4, 5, 6, 7, 8, 9, 10 ]

// console.log([1,2,[4,5,6,[[7,8],9]],10]);
// console.log(flatten([1,2,[4,5,6,[[7,8],9]],10])); // -> [ 1, 2, 4, 5, 6, 7, 8, 9, 10 ]