Nodejs Utililty Methods Array Reduce

Array.prototype.reduce = function(fn, initial)
    var r, i;
    initial ? r = initial : r = this[0];
    for (i=1;i<this.length;i++)
        r = fn(r, this[i]);
    return r;
...

Array.prototype.reduce = function (fn, initialValue) {
  let acc = initialValue
  for (var i = 0; i < this.length; i++) {
    acc = fn(acc, this[i], i)
  return acc
Array.prototype.forEach = function (fn) {
  this.reduce((acc, curr, i) => {
...

if (!Array.prototype.reduce) {
  Array.prototype.reduce = function(fun ) {
    var len = this.length >>> 0;
    if (typeof fun != "function")
      throw new TypeError();
    if (len == 0 && arguments.length == 1)
      throw new TypeError();
    var i = 0;
    if (arguments.length >= 2) {
...

Array.prototype.reduce = function(fun )
  var len = this.length;
  if (typeof fun != "function") {
    throw new TypeError();
  if (len == 0 && arguments.length == 1) {
    throw new TypeError();
  var i = 0;
  if (arguments.length >= 2) {
    var rv = arguments[1];
  } else {
    do {
      if (i in this) {
        rv = this[i++];
        break;
      if (++i >= len) {
        throw new TypeError();
    } while (true);
  for (; i < len; i++) {
    if (i in this) {
      rv = fun.call(null, rv, this[i], i, this);
  return rv;
};

Array.prototype.reduce = Array.prototype.reduce || function(fun ) {
    var len = this.length >>> 0;
    if (typeof fun != "function") {
        throw new TypeError();
    if (len == 0 && arguments.length == 1) {
        throw new TypeError();
    var i = 0;
...

'use strict';
Array.prototype.reduce = function(pasteback, initial){
  for(var i = 0
      , c =  this.length
      , value = arguments.length>1 ? initial : this[i++]
  ; i<c; i++){
    value = pasteback(value, this[i], i, this);
  return value;
...

Array.prototype.reduce = function(process, initial) {
  var value = initial;
  for (var i = 0; i < this.length; i++) {
    if( ( i === 0 ) && ( value === undefined || value === null ))
        value = this[0];
        continue;
    value = process( value, this[i] );
...

Array.prototype.reduce = function(process, initial) {
  if (initial === undefined) {
    var slice = this.slice(1);
    initial = this[0];
  var array = slice || this;
  array.forEach(function(value) {
    initial = process(initial, value);
  });
...

Array.prototype.reduce = function(reducingFunction, initialValue) {
  var result = initialValue;
  this.forEach(function(x) {
    reducingFunction(result, x)
  });
  return result;

Array.prototype.reduce = function(t, fn) {
  for(var i = 0 ; i < this.length ; i++) {
    t = fn(t, this[i])
  return t