Nodejs Utililty Methods Array Sum

Array.prototype.sum = function ( iterator ) {
  "use strict";
  var i = ( typeof iterator === "undefined" ) ?  0 : iterator,
    total = 0;
  if ( this[ i ] instanceof Array ) {
    for ( i; i < this.length; i++) {
      total += this[i].sum();
  else {
    for (i = 0; i < this.length; i++) {
      total += this[i];
  return total;
};

Array.prototype.sum = function() {
  return this.reduce(function(a,b){return a+b;});
};

Array.prototype.sum=function(){
  var suma;
  for(var i=0;i<this.lenght;i++){
    suma=suma+this[i];
  return suma;

Array.prototype.sum = function () {
  let s = 0;
  for (let i = 0; i < this.length; i++) {
    s += this[i];
  return s;
};

Array.prototype.sum = function() {
  var sum = 0;
  for (var i = 0, l = this.length; i < l; i++) {
    sum += this[i];
  return sum;
};

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

Array.prototype.sum = function() {
    var res = 0;
    for(var p in this)
  res += this[p];
    return res;
};
var s = [1, 2, 3].sum();

Array.prototype.sum = function() {
  return this.reduce(function(prev, curr) {
    return prev + curr;
  });
};
module.exports = Array.prototype.sum;

Array.prototype.sum  = function() {
    var res = 0;
    for(var p in this)
  res += this[p];
    return res;
};
var a = [1, 2, 3];
console.log(0 in a);

Array.prototype.sum = function() {
    var res = 0;
    for(var i=0;i<this.length;++i)
  res += this[i];
    return res;
};
var s = [1, 2, 3].sum();