Prototypal Inheritance in NodeJS

Question

I am learning NodeJS and learning prototypal inheritance.

Below is the code I am using for prototypal inheritance .

The issue I am facing is :

The meow, purr and hiss methods do get called on leopardObj.

But , whenever I call below methods , inside those methods , this.name is always coming as undefined.

leopardObj.meow();
leopardObj.purr();
leopardObj.hiss();

Can anybody please help me as I am not able to understand why this.name is coming as undefined ?

function Cat(name){
    console.log("Inside Cat before = ",name);
    this.name = name
    console.log("Inside Cat after = ",this.name);
}
Cat.prototype.meow = () => {  
    console.log(this);
    console.log("Meow for !!",this.name);
}


function Lynx(name){
    console.log("Inside Lynx with name = ",name);
    Cat.call(this,name);
}
Lynx.prototype = Object.create(Cat.prototype);
Lynx.prototype.purr = () => {
    console.log("Purr for !! ",this.name);
}


function Leopard(name){
    console.log("Inside Leopard with name = ",name);
    Lynx.call(this,name);
}
Leopard.prototype = Object.create(Lynx.prototype);
Leopard.prototype.hiss = () => {
    console.log("Hiss for !! ",this.name);
}
const leopardObj = new Leopard("Sheryl");
leopardObj.meow();
leopardObj.purr();
leopardObj.hiss();

Viktor Gusev · Accepted Answer · 2021-04-15 11:57:55Z

1

meow, purr and hiss functions are arrow functions, so you have bind your context incorrectly. Change them to regular functions back and everything will work as expected:

Leopard.prototype.hiss = function() {
    console.log("Hiss for !! ", this.name);
}

answered Apr 15, 2021 at 11:57

Viktor Gusev

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