Nodejs Utililty Methods Array Sum

Array.prototype.sum = function (fun) {
    var result = 0;
    this.forEach(x => result += fun ? fun(x) : x);
    return result;
};

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

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

Array.prototype.sum = function (s) {
  s = s || Selector;
  var l = this.length;
  var sum = 0;
  while (l-- > 0) sum += s(this[l]);
  return sum;
};

Array.prototype.sum = function(selector) {
    if (typeof selector !== 'function') {
        selector = function(item) {
            return item;
    var sum = 0;
    for (var i = 0; i < this.length; i++) {
        sum += selector(this[i]);
...

Array.prototype.sum = function(selectorfun)
  if (selectorfun)
    return this.map(selectorfun).sum();
  else
    var ret = 0;
...

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

Array.prototype.sumArrayItems = function() {
  var countIndex = this.length - 1;
  var sum =0;
  while ( countIndex >= 0) {
    sum = sum + this[ countIndex ];
    countIndex--;
  return sum;
var findMissing = function( arr1 , arr2 ) {
  return Math.abs( arr1 - arr2);
findMissing([1,2].sumArrayItems() , [1,2,5].sumArrayItems());

Array.prototype.sumItems = function(){
  var sum = 0;
  for(var i=0; i<this.length; i++){
    sum=sum+this[i];
  return(sum);
var arr = new Array;
arr = [5,10];
...