JavaScript Prototype Inheritance did not work

Question

I have an object called superCar. I have a function Car. I would like to inherit my Car Object from superCar Object. Here is my code:

var superCar = {
model : "sedan"
};
function Car(){
  this.name = null;
}

var c1 = new Car();
c1.name="Toyota";

var c2 = new Car();
c2.name="Bmw";

console.log(c1.name);
console.log(c2.name);

c1.__proto__.__proto__ = superCar.__proto__ ;

console.log(c1.model);

I am expecting the out put will be "Toyota" , "Bmw" , "sedan". But the output is comming out as "Toyota" , "Bmw" , "undefined". Can any one of you please explain why my inheritance did not work?

Mark · Accepted Answer · 2018-09-29 03:30:08Z

You are mixing inheritance patterns up a bit. Your inheritance isn't working because model isn't on the superCar prototype chain, it's directly on the object itself.

You can make superCar a function like car and tie it into the inheritance chain like:

function superCar(){
    this.model = "sedan"
};
function Car(){
    superCar.call(this)  // this will add model and other properties assigned in the constructor 
    this.name = null;
}
Car.prototype  = Object.create(superCar.prototype); // this will add protoype methods from superCar, but there aren't any
  
var c1 = new Car();
 c1.name="Toyota";
    
var c2 = new Car();
c2.name="Bmw";
    
console.log(c1.name);
console.log(c2.name);
console.log(c1.model);
console.log(c2.model);

Alternatively you can use Object.create to create a prototype-link to the object superCar with something based on this:

let superCar ={
    model: "sedan"
};
function Car(name){
   let obj = Object.create(superCar) // obj will delegate to superCar when it doesn't find a property
   obj.name = name
   return obj
}
  
var c1 =  Car("Toyota");
var c2 =  Car("Bmw");
    
console.log(c1.name);
console.log(c2.name);
console.log(c1.model);
console.log(c2.model);

You might be able to do a mix of these two pattern, but it's going to be confusing.

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