The implementation of reduceRight function in JavaScript by for loop

array-reduce-right.js

Array.prototype.reduceRightFunc = function(callbackFn, initialValue) {
  let accumulator = initialValue, index = this.length - 1;
  if (initialValue === undefined) {
    if (!this.length) {
      throw new TypeError("Reduce of empty array with no initial value");
    } else {
      accumulator = this[this.length - 1];
      index = this.length - 2;
    }
  }

  for (; index >= 0; index--) {
    accumulator = callbackFn(accumulator, this[index], index, this);
  }

  return accumulator;
}