#137 Overriding constructor

easy

javascript

Consider the following code:

class Person {
  constructor(name) {
    this.name = name;
  }
}

class Student extends Person {
  constructor(name, studentId) {
    this.name = name;
    this.studentId = studentId;
  }
}

// Doesn't work!

let student = new Student("Pawan Kumar", 1); // Error: this is not defined.

Why there is an error when creating object of student class? How to fix it?

The error occurs because the Student class constructor does not call the super constructor of the Person class. In JavaScript, when a class extends another class, the derived class's constructor must call super() before accessing this.

To fix this, you need to call super(name) in the Student constructor before you can use this. Here's the corrected code:

class Person {
  constructor(name) {
    this.name = name;
  }
}

class Student extends Person {
  constructor(name, studentId) {
    // Call the constructor of the Person class

    super(name);
    this.studentId = studentId;
  }
}

// Works correctly now

let student = new Student("Pawan Kumar", 1);
console.log(student.name);      // Output: Pawan Kumar

console.log(student.studentId); // Output: 1