simplest inheritance in javascript?

Question

I am trying to use OOPs in javascript. What i am trying is,

I have 2 classes say classA and classB. I am inheriting classA in classB. Like :

 function classA(){
    this.propA = "somevalue of A";
 }

 function classB(){
    classB.prototype = new classA();              //inheriting
    classB.prototype.constructor = classB;        //updating constructor defination
    this.propB = "somevalue of B";
 }

Now i created the object of classB :

var classBObject = new classB();

and than trying to access base class property value with :

alert(classBObject.propA);      //here i am expecting "somevalue of A"

but the alert shows me empty. Can anybody please tell me what i am doing wrong here ?

Javascript is a prototype-based language, not a class-based language. So, technically there are no classes. In Javascript, objects inherit directly from other objects, unlike in other class-based languages, where objects inherit from classes. There are 5 types in Javascript: String, Number, Boolean, Undefined, and Null. Everything else is an object. — Tuan
– Tuan, Commented Feb 14, 2013 at 8:19

KooiInc · Accepted Answer · 2013-02-14 07:04:41Z

3

Move the prototype assignment of classB outside the constructor:

function classA(){
    this.propA = "somevalue of A";
 }

 function classB(){
    // classB.prototype.constructor = classB;
    // ^ no need for this, constructor will be overwritten
    //   by classB.prototype = new classA
    this.propB = "somevalue of B";
 }

 classB.prototype = new classA; // assing prototype for classB here

edited Feb 14, 2013 at 7:04

answered Feb 14, 2013 at 6:50

KooiInc

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