Ways to extend Array object in javascript

Question

i try to extend Array object in javascript with some user friendly methods like Array.Add() instead Array.push() etc...

i implement 3 ways to do this. unfortunetly the 3rd way is not working and i want to ask why? and how to do it work.

//------------- 1st way Array.prototype.Add=function(element){      this.push(element); };  var list1 = new Array(); list1.Add("Hello world"); alert(list1[0]);  //------------- 2nd way function Array2 () {     //some other properties and methods };  Array2.prototype = new Array; Array2.prototype.Add = function(element){   this.push(element);   };  var list2 = new Array2; list2.Add(123); alert(list2[0]);  //------------- 3rd way function Array3 () {     this.prototype = new Array;     this.Add = function(element){       this.push(element);       }; };  var list3 = new Array3; list3.Add(456);  //push is not a function alert(list3[0]); // undefined 

in 3rd way i want to extend the Array object internally Array3 class. How to do this so not to get "push is not a function" and "undefined"?

Here i add a 4th way.

//------------- 4th way function Array4 () {     //some other properties and methods     this.Add = function(element){         this.push(element);     };  }; Array4.prototype = new Array();  var list4 = new Array4(); list4.Add(789); alert(list4[0]); 

Here again i have to use prototype. I hoped to avoid to use extra lines outside class constructor as Array4.prototype. I wanted to have a compact defined class with all pieces in one place. But i think i cant do it otherwise.

Answer 1

ES6

class SubArray extends Array {     last() {         return this[this.length - 1];     } } var sub = new SubArray(1, 2, 3); sub // [1, 2, 3] sub instanceof SubArray; // true sub instanceof Array; // true 

---

Using __proto__

(old answer, not recommended, may cause performance issues)

function SubArray() {   var arr = [ ];   arr.push.apply(arr, arguments);   arr.__proto__ = SubArray.prototype;   return arr; } SubArray.prototype = new Array; 

Now you can add your methods to SubArray

SubArray.prototype.last = function() {   return this[this.length - 1]; }; 

Initialize like normal Arrays

var sub = new SubArray(1, 2, 3); 

Behaves like normal Arrays

sub instanceof SubArray; // true sub instanceof Array; // true