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Javascript new array prototype in new object constructor

If I do:

Array.prototype.test = "test"
Array.prototype.t = function() {return "hello"}


Every new Array will have the property test and the method t.

Array

test

t

How can I do the same without affecting all Arrays?

Like:

Names = function(arr){
// Contacts constructor must be the same of Array
// but add the property test and the function t
}
z=new Names(["john","andrew"])


So that z.test will return "test" and z.t() will return "hello"?
(but Array.test and Array.t would stay undefined)

z.test

"test"

z.t()

"hello"

Array.test

Array.t

undefined

I explain better:

Array.prototype.t="test";
Array.prototype.test = function(){ return "hello";}

z=new Array("john", "andrew")
console.log(z);

But this affects ALL arrays.
I want the same but with a new constructor Names that inherits Array constructor.

// Contacts constructor must be the same of Array

Names

Array.prototype

5 Answers
5

Can't you just extend Array?

Array

class Names extends Array {
constructor(...args) {
super(...args);
this.t = "test";
}

test() { return "hello" }
}

let z = new Names("john", "andrew")


Prototype is bind to the native type and every other element of that type will inherit prototyped properties.

If you need them for an instance only use objects.

var z = {
t : function(){
console.log("hello");
},
test : "test"
};

z.t();
console.log(z.test);

Here is a crude implementation:

function Names(arr) {
this.contacts = enhanceArray(arr);
}

function enhanceArray(arr) {
arr.test = 'helloProp';
arr.t = function() {
return 'helloFunc'
}
return arr;
}
let z = new Names(["john", "andrew"]);

console.log(z.contacts[0]);
console.log(z.contacts.test);
console.log(z.contacts.t());

You can create your own extended Array constructor factory, something like

(() => {
const myArr = XArray();
let a = myArr(["John", "Mary", "Michael"]);
console.log(`myArr(["John", "Mary", "Michael"]).sayHi(1): ${a.sayHi(1)}`);
console.log("demo: myArr(1, 2, 3) throws an error");
let b = myArr(1, 2, 3); // throws

// an extended array
function XArray() {
const Arr = function(arr) {
if (arr.constructor !== Array) {
throw new TypeError("Expected an array");
}
this.arr = arr;
};
Arr.prototype = {
sayHi: function (i) { return `hi ${this.arr[i]}`; }
};
return arr => new Arr(arr);
}
})();

class Names extends Array {
constructor(...args) {
super(...args);
}
}

Names.prototype.t = 'test';

let z = new Names("john", "andrew")
z.push('Amanda')

console.log(z.t)
console.log(z)

You can easily set it at Names.prototype

Names.prototype

z

z

t

Array

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