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How to Extend a JavaScript Class?

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To extend a JavaScript class, we can use the extends keyword and the class syntax.

For instance, we can write:

class Person {
  sayHello() {
    console.log('hello');
  }

  walk() {
    console.log('I am walking!');
  }
}

class Student extends Person {
  sayGoodBye() {
    console.log('goodbye');
  }

  sayHello() {
    console.log('Hi, I am a student');
  }
}

const student1 = new Student();
student1.sayHello();
student1.walk();
student1.sayGoodBye();

console.log(student1 instanceof Person);
console.log(student1 instanceof Student);

We have the Person class that serves as the base class for the Student class.

It has the sayHello and walk methods.

Then we have the Student class which inherits the contents of the Person class.

It also has its own methods, which are sayGoodBye and sayHello .

The extends keywords indicates that Student has Person as its base class, so it should also inherit methods from the Person class.

Next, we create a new Student instance with the new keyword.

And we call all the methods from the Student class itself and the Person class from student1 .

Also, both console logs should log true because student1 is a Student instance and Student ‘s base class is Person .

By John Au-Yeung

Web developer specializing in React, Vue, and front end development.

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