How does inheritance work in ES5-Javascript?

Question

For the below code,

           var customer={
                name: "Tom Smith",

                speak: function(){
                    return "My name is " + this['name'];
                },

                address: {
                    street: '123 Main St',
                    city: "Pittsburgh",
                    state: "PA"
                }
            };

Below is my visualisation of customer object,

My question:

Does customer object inherit properties(built-ins) of Object.prototype only?

Are the properties(built-ins) of Object function type object are also for the purpose of inheritance?

If yes, What is the syntax for customer object to inherit Object properties?

Anyhow, objects don't really inherit properties so much as they have a prototype chain of objects which property access will traverse. — Alexander O'Mara
– Alexander O'Mara, Commented Dec 2, 2015 at 18:25
@AlexanderO'Mara the suggested answer use [[Prototype]], which in my case, customer.[[Prototype]] is Object.prototype. But my question is, Does JS allow customer inherit Object properties as well? Is this a duplicate query? — overexchange
– overexchange, Commented Dec 2, 2015 at 18:29
Oh, you mean you the static-like methods of the Object constructor? They are not inherited, and normally you wouldn't need to do this, they are globally accessible. — Alexander O'Mara
– Alexander O'Mara, Commented Dec 2, 2015 at 18:31

Community · Accepted Answer · 2017-05-23 11:59:20Z

2

Below is my visualisation of customer object

It would be better if you used the term [[prototype]] instead of __proto__ - as you can see, .__proto__ is just a getter/setter inherited from Object.prototype.

Does customer object inherit properties(built-ins) of Object.prototype only?

Yes. Though you could add your own properties to Object.prototype, they would be inherited as well, it's not only the built-in ones.

Are the properties(built-ins) of Object are also for the purpose of inheritance?

No. They're static functions that are supposed to be called with objects as their arguments, not object methods.

What is the syntax for customer object to inherit Object properties?

Object is a function and usually you don't want to inherit from it. If you really wanted, you could use Object.create(Object).

Also, ES6 adds a new way to do that, as classes inherit static methods from their parent as well:

class MyObject extends Object {
    static myCreate(x) {
        return this.create(x);
    }
}

edited May 23, 2017 at 11:59

CommunityBot

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answered Dec 2, 2015 at 18:29

Bergi

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6 Comments

overexchange Over a year ago

Do you see any mistake in above screenshot? apart from [[Prototype]] naming convention?

Bergi Over a year ago

@overexchange: Customer should be customer. And you definitely need to do something about the arrows, though that's only a usability concern not one of correctness

overexchange Over a year ago

Arrows? I did not get u.

Bergi Over a year ago

I found those arrows between the boxes to be very hard to decipher visually. Those two crossings, uh, it's only one, and the merge, look too similar…

overexchange Over a year ago

After your suggestions, Is this fine now?

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