Object Oriented Javascript - How To Define A Class Within A Class? from a C# example

Question

I know there are a lot of OO javascript questions on SO and I a have been reading a lot of resources.... BUT it is still far my most long winded learning curve so far!

I am not classically trained sorry, hence I will have to just show you guys in c# an example of what I want to acheive.

I hope you can help!

public class Engine
{
    public int EngineSize;

    public Engine()
    {
    }
}
public class Car
{
    public Engine engine;

    public Car()
    {
        engine = new Engine();
    }
}

guys I am not really worried about the private/public & naming conventions of the above C# example.

All I want to know is how to replicate this structure in Javascript?

Thanks!

Is this supposed to be C#? What are the parens after public class ...? — Mehrdad Afshari
– Mehrdad Afshari, Commented Aug 24, 2009 at 15:33

Christian C. Salvadó · Accepted Answer · 2009-08-24 15:48:12Z

16

function Engine(size) {
    var privateVar;

    function privateMethod () {
      //...
    }

    this.publicMethod = function () {
       // with access to private variables and methods
    };

    this.engineSize = size; // public 'field'
}

function Car() { // generic car
    this.engine = new Engine();
}

function BMW1800 () {
  this.engine =  new Engine(1800);
}

BMW1800.prototype = new Car(); // inherit from Car


var myCar = new BMW1800();

answered Aug 24, 2009 at 15:48

Christian C. Salvadó

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1 Comment

PanCrit Over a year ago

I like this better than the other examples here because it uses javascript ability to provide a private namespace that isn't accessible from the outside. I'd have showed the same thing with the car as well, but at least your privateVar demonstrates information hiding.

Paul Dixon · Accepted Answer · 2009-08-24 15:38:32Z

3

So you really just want to know how one object can contain another? Here's a very simple conversion of your sample:

function Engine()
{
    this.EngineSize=1600;
}

function Car()
{
    this.engine=new Engine();
}

var myCar=new Car();

answered Aug 24, 2009 at 15:38

Paul Dixon

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Comments

score 1 · Accepted Answer · 2020-08-01 21:39:30Z

1

Here is an answer with ES6:

class Engine {
  // Constructor, size defaults to 1
  constructor(size = 1) {
    // Sets size to size
    this.size = size;
  }
  // Method
  start() {
    for (let i = 0; i < this.size, i++) {
      alert('Brrr');
    }
  }
}
class Car {
  // Constructor
  constructor(name) {
    // Sets engine to a new engine
    this.engine = new Engine();
    // Sets name to name
    this.name = name;
  }
  // Method
  introduceTo(name) {
    alert(`Hey ${name}, here is my car ${this.name}.`);
  }
}

let myCar = new Car('Ferrari');
myCar.engine = new Engine(5);
myCar.introduceTo('bro');
myCar.engine.start();

(I made some additions hopefully you like it)

edited Aug 1, 2020 at 21:39

answered Aug 1, 2020 at 21:27

user13288978

Comments

Eldar Djafarov · Accepted Answer · 2009-08-24 15:43:22Z

0

function Engine(){ // this is constructor. Empty since Engine do nothing. 
}
Engine.prototype.EngineSize=null; // this is public property

function Car(){ // this is Car constructor. It initializes Engine instance and stores it in Engine public property
    this.Engine =new Engine();
}

Car.prototype.Engine =null;

When you will make new Car instance. Car constructor will create new instance of Engine and assign it to Engine property of Car instance.

answered Aug 24, 2009 at 15:43

Eldar Djafarov

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