JS nested inheritance

Question

I'm not able to properly override an inherited object and wondering if I can get a hand here. Been stuck for 3 days already.

say

function Person() { 
    function getValue(){
        serviceArea();
    }

    function serviceArea() {
        alert('Old Location');
    }

    return {
        getValue: getValue,
        serviceArea: serviceArea
    }
}

then

function Student() {};
Student.prototype = new Person();
Student.prototype.serviceArea = function() { alert('New Location'); };
var bobStu = new Student();

when I run bobStu.serviceArea(); I get 'New Location', however when I run bobStu.getValue(); I get 'Old Location'

I'm passing this bobStu.getValue(); down a method that needs to call the overridden method but I can't get it to do that. Can you explain why getValue() is calling the old serviceArea()? and how to do it properly?

I've been readying this article many times and feel like it is telling me something but I'm too burnt that I can't get it :( https://developer.mozilla.org/en-US/docs/Web/JavaScript/Introduction_to_Object-Oriented_JavaScript#Namespace

Your Person is a factory function, not a classical constructor, and it's scoping does not care about properties. — Bergi
– Bergi, Commented Sep 27, 2016 at 23:00
You might find the answer in this thread stackoverflow.com/questions/12183011/… useful. — Rosa
– Rosa, Commented Sep 27, 2016 at 23:08

Freyja · Accepted Answer · 2016-09-27 22:49:04Z

3

Using just serviceArea() refers only to the function serviceArea defined in the scope of Person:

function Person() { 
    function getValue(){
        serviceArea();  // this...
    }

    // ...always refers to this, independent of the object you're constructing
    function serviceArea() {
        alert('Old Location');
    }

    // also note this:
    this.getValue = getValue;
    this.serviceArea = serviceArea;
}

Use this.serviceArea() instead if you want to use the serviceArea methods implemented by subclasses.

Also, constructors shouldn't return values; attach the values directly to the this value instead.

answered Sep 27, 2016 at 22:49

Freyja

41.3k9 gold badges89 silver badges130 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

JS nested inheritance

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related