Javascript nested class

Question

How do I define nested class in Java Script.

Here is the code snippet I have:

objA = new TestA();

function TestB ()
{
   this.testPrint = function ()
  {
     print ( " Inside testPrint " );
  }
}

function TestA ()
{
   var myObjB = new TestB();
}

Now I am trying to access testPrint using objA

objA.myObjB.testPrint();

But its giving error "objA has no properties"

How can I access testB method using objA handler?

Lorenzo Polidori · Answer 1 · 2013-06-30T07:51:50.927

If you want the prototype definition of the inner nested classes to be not accessible from outside the outer class, as well as a cleaner OO implementation, take a look at this.

var BobsGarage = BobsGarage || {}; // namespace

/**
 * BobsGarage.Car
 * @constructor
 * @returns {BobsGarage.Car}
 */
BobsGarage.Car = function() {

    /**
     * Engine
     * @constructor
     * @returns {Engine}
     */
    var Engine = function() {
        // definition of an engine
    };

    Engine.prototype.constructor = Engine;
    Engine.prototype.start = function() {
        console.log('start engine');
    };

    /**
     * Tank
     * @constructor
     * @returns {Tank}
     */
    var Tank = function() {
        // definition of a tank
    };

    Tank.prototype.constructor = Tank;
    Tank.prototype.fill = function() {
        console.log('fill tank');
    };

    this.engine = new Engine();
    this.tank = new Tank();
};

BobsGarage.Car.prototype.constructor = BobsGarage.Car;

/**
 * BobsGarage.Ferrari
 * Derived from BobsGarage.Car
 * @constructor
 * @returns {BobsGarage.Ferrari}
 */
BobsGarage.Ferrari = function() {
    BobsGarage.Car.call(this);
};
BobsGarage.Ferrari.prototype = Object.create(BobsGarage.Car.prototype);
BobsGarage.Ferrari.prototype.constructor = BobsGarage.Ferrari;
BobsGarage.Ferrari.prototype.speedUp = function() {
    console.log('speed up');
};

// Test it on the road

var car = new BobsGarage.Car();
car.tank.fill();
car.engine.start();

var ferrari = new BobsGarage.Ferrari();
ferrari.tank.fill();
ferrari.engine.start();
ferrari.speedUp();

// var engine = new Engine(); // ReferenceError

console.log(ferrari);

This way you can have prototype inheritance and nested classes so that classes defined within BobsGarage.Car are not accessible outside the constructor of BobsGarage.Car but instances of them are accessible to derived classes, as shown in the test code.

Note: I am referring to the concept of Class in Javascript as defined on the MDN.

score 7 · Answer 2 · answered Oct 09 '08 at 02:19

7

use this.myObjB instead of var myObjB

answered Oct 09 '08 at 02:19

Leo

2,860
3
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21

score 3 · Answer 3 · edited May 23 '17 at 12:32

3

Object literals:

var objA = {
    myObjB: {
       testPrint: function(){
          print("Inside test print");
       }
    }
};

objA.myObjB.testPrint();

edited May 23 '17 at 12:32

Community

1
1

answered Oct 09 '08 at 02:23

Aaron Maenpaa

119,832
11
95
108

Who voted this down? This is a perfectly valid answer, missing only "objA.myObjB.testPrint()"! – Robert K Oct 09 '08 at 02:27
When we refer to "this" inside the testPrint method, are we referring to myObjB or objA? – Slavo Feb 27 '12 at 16:23
To answer my previous question - it's objA, so this doesn't seem like a good implementation of namespaces. – Slavo Feb 27 '12 at 16:29
this isn't using classes, objA and myObjB are both just objects – what is sleep Aug 06 '14 at 20:01

score 1 · Answer 4 · answered Oct 09 '08 at 02:46

If you're trying to do inheritance then you may want to consider the prototype keyword.

var myObjB = function(){
    this.testPrint = function () {
       print ( " Inside testPrint " );
    }
}

var myObjA = new myObjB();
myObjA.prototype = {
   var1 : "hello world",
   test : function(){
      this.testPrint(this.var1);
   }
}

(i hope that made sense)

score 1 · Answer 5 · edited Jan 15 '16 at 12:53

1

Your definition of TestA does not expose any public members. To expose myObjB, you need to make it public:

function TestA() {
    this.myObjB = new TestB();
}
var objA = new TestA();
var objB = objA.myObjB;

edited Jan 15 '16 at 12:53

Lee Goddard

10,680
4
46
63

answered Oct 09 '08 at 03:49

harley.333

3,696
2
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iNeobee · Answer 6 · 2022-07-16T14:53:08.647

0

this is another way to do that.

class A {
  constructor(classB) {
    this.ObjB = classB
  }
}

class B {
  Hello() {
    console.log("Hello from class B")
  }
}

let objA = new A(new B())

objA.ObjB.Hello()

edited Jul 16 '22 at 14:53

answered Jul 16 '22 at 14:50

iNeobee

1
1

Javascript nested class

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