Nodejs Utililty Methods Array Filter

Array.prototype.filter = function (test) {
    var i, item, newArray = [];
    for (i = 0; i < this.length; i++) {
  item = this[i];
  if (test(item)) {
      newArray.push(item);
    return newArray;
...

Array.prototype.filter = function(testFunction){
  var result = [];
  this.forEach(function(item){
    if(testFunction(item)){
      result.push(item);
  })
  return result;

'use strict'
Array.prototype.cs142filter = function(element, func) {
  var result = [];
  var array = Object(this);
  var length = array.length;
  for (var i = 0; i < length; i++) {
    var val = array[i];
    if (func.call(undefined, element, val)) {
      result.push(val);
...

Array.prototype.customFilter = function(fn) {
  let results = [];
    for (let i = 0; i < this.length; i++) {
        let itemExists = fn(this[i]);
        if (itemExists) {
            results.push(this[i]);
  return results;
...

Array.prototype.filterByField = function(field, key) {
  var newArray = [];
  for (var i = 0; i < this.length; i++) {
    if (this[i][field] == key) {
      newArray.push(this[i]);
  return newArray;
};
...

Array.prototype.filterByField = function (field, value)
    var list = this;
    var listReturn = [];
    list.forEach(function(item)
        if (item[field] === value)
            listReturn.push(item);
...

Array.prototype.filterEmpty = function ()
    var arr = this;
    var i = arr.length;
    while (i--)
        if (arr[i] instanceof Array)
            arr[i] = arr[i].filterEmpty();
...

Array.prototype.filterSync = async function (callback, thisArg) {
  let filterResult = await Promise.all(this.map(callback))
  return this.filter((_, index) => filterResult[index])

Array.prototype.filterUnique = function() {
    'use strict';
    var arr = [];
    var orig = this;
    orig.forEach(function(a, i) {
        if (arr.indexOf(a) < 0) {
            arr.push(a);
        } else {
            orig.splice(i, 1);
...

Array.prototype.mfilter =  function (fun) {
  var filtered = [];
  for(let i = 0; i < this.length; i++) {
    if (fun(this[i], i, this)) filtered.push(this[i]);
  return filtered;
};
var returnarr = [1,2,3,4,5,6].mfilter(function(element, index, arr) {
  return element > 5;
...