Javascript Inheritance Chain

Question

function Student() {
}

Student.prototype.sayName = function() {
  console.log(this.name)
}

function EighthGrader(name) {
  this.name = name
  this.grade = 8
}

EighthGrader.prototype = Object.create(Student)

const carl = new EighthGrader("carl")
carl.sayName() // console.logs "carl" TypeError HERE
carl.grade // 8

Why do I get a TypeError when I use Student as the argument for Object.create? I know it can be fixed using Student.prototype instead.

I thought the sayName() method could still be accessed according to the prototype chain?

score 1 · Answer 1 · answered Oct 20 '21 at 22:50

You are getting this error because sayName is not defined on Student and therefore not on EighthGrader.prototype. sayName is defined on Student.prototype, so the following is the correct way of establishing inheritance:

EighthGrader.prototype = Object.create(Student.prototype);

Inheritance always works by having the child class' prototype "inherit" from the parent class' prototype.

See also Benefits of using `Object.create` for inheritance

Javascript Inheritance Chain

1 Answers1