Inheriting from a parent object will execute its parent constructor?

Question

All , In the classical inheritance language. such as Java , c# etc, It is true a new instance initialization of a sub Class will cause the base Class constructor execution before the sub Class's constructor is executed. But I am not sure whether It will be same in the javascript inheritance. Let's take a example . Says your have the code like below .

function Shape() {
    this.x = 0;
    this.y = 0;
};

If there is an object name rect inherit from Shape . supposed the constructor of Rectangle looks like this.

function Rectangle(){

};
Rectangle.prototype = Object.create(Shape.prototype);
var rect= new Rectangle();

Would the constructor Shape will be executed when the constructor Rectangle is executed ? thanks.

In Javascript there is no concept as constructors, everything is functions. reference : **www.crockford.com/javascript/inheritance.html** — dreamweiver, Apr 21 '13 at 07:26
Really ?What I had knew is when the `new` expression is executed, the `function` becomes the object's constructor. without the `new` , the function is just a block of code . — Joe.wang, Apr 21 '13 at 07:30
How difficult is it to add an `alert` in the parent's constructor ? — Nir Alfasi, Apr 21 '13 at 07:46
@alfasin I see. I already knew the answer. I just don't know why . thanks. — Joe.wang, Apr 21 '13 at 07:49

score 1 · Accepted Answer · edited May 23 '17 at 11:50

1

This is how you normally do inheritance in JavaScript:

function Shape() {
    this.x = 0;
    this.y = 0;
}

function Rectangle() {
    Shape.call(this);
}

Rectangle.prototype = Object.create(Shape.prototype);

Notice that you're calling Shape.call(this) from inside the Rectangle constructor. This is like calling the base/super class constructor in other languages. Without doing so your Rectangle objects would not have the x and y properties defined inside the Shape constructor.

For more details read the following answer: https://stackoverflow.com/a/15497685/783743

edited May 23 '17 at 11:50

Community

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answered Apr 21 '13 at 08:15

Aadit M Shah

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Thanks your kindly answer , It is nice to meet you again. :) actually I found what I really want to ask is another question. Could you please review [here](http://stackoverflow.com/questions/16129365/in-prototype-inheritance-program-when-a-property-not-found-in-a-specified-object) – Joe.wang Apr 21 '13 at 08:40

Inheriting from a parent object will execute its parent constructor?

1 Answers1