Iterate over a JavaScript array from right to left

Array.prototype.forEach() is pretty convenient, but what if you want to iterate over an array from right to left? Using a for loop is an option, but there are more elegant tools at our disposal.

Reversing an array can be easily accomplished using Array.prototype.reverse(), but it mutates the original array. In order to avoid that, we have to create a shallow clone, using Array.prototype.slice(). This needs to be done prior to reversing to avoid the original array being mutated. Finally, we can use Array.prototype.forEach() to iterate over the reversed array.

const forEachRight = (arr, callback) =>
  arr.slice().reverse().forEach(callback);

forEachRight([1, 2, 3, 4], val => console.log(val)); // '4', '3', '2', '1'