Javascript "class" extension with parameters?

Question

I would like to "extend" a new class from an existing class and include it's methods and parameter construction.

System = function(name, hp){
  this.name = name;
  this.hp = [];
  this.setHP = function(hp){
     this.hp[0] = hp;
     this.hp[1] = hp;
  }
  this.setHP(hp);
}

Weapon = function(name, hp){
   System.call(this);
}

Weapon.prototype = new System(name, hp);
Weapon.prototype.constructor = Weapon;


var gun = new Weapon("Gun", 10);    // undefined name, hp
var hangar = new System("Hangar", 10);    // works

So, this is as far as i got, and someone is obviously wrong. Can someone advise me ?

`call` requires parameters `Weapon = function(name, hp){ System.call(this, name, hp); }` — Dhaval Marthak, Apr 10 '15 at 08:05
May i inquire about which solution better to use ? Expand the call or use apply as suggested ? — Christian F, Apr 10 '15 at 08:42
@Cristian F [this](http://stackoverflow.com/questions/1986896/what-is-the-difference-between-call-and-apply) might be helpful — Dhaval Marthak, Apr 10 '15 at 08:51

score 1 · Answer 1 · answered Apr 10 '15 at 08:06

You need to pass the arguments in the call:

System.call(this, name, hp);

Also, be aware that Weapon.prototype = new System(name, hp); can have side-effects, it is better practice to use:

Weapon.prototype = Object.create(System.prototype);

You can find polyfills for Object.create if you need to support ancient browsers.

score 1 · Answer 2 · answered Apr 10 '15 at 08:09

System = function(name, hp){
  this.name = name;
  this.hp = [];
  this.setHP = function(hp){
     this.hp[0] = hp;
     this.hp[1] = hp;
  }
  this.setHP(hp);
}
Weapon = function(name, hp){
    System.apply(this, arguments);
}

console.log(new Weapon("Gun", 10));
console.log(new System("Hangar", 10));

Result:

Weapon {name: "Gun", hp: Array[2], setHP: function}
System {name: "Hangar", hp: Array[2], setHP: function}

Javascript "class" extension with parameters?

2 Answers2