JavaScript extends

The extends keyword can be used to extend the objects as well as classes in JavaScript. The extends keyword can be used to subclass custom classes as well as built-in objects. In another word, its used to create a class that is a child of another class.

class childclass extends parentclass {
     //...}

class parentclass extends in-built object {
    //...}

JavaScript extends

Simple example code.

JavaScript extends class

inherit the methods from the “Car” class:

<!DOCTYPE html>
<html>
<body>
  <script>
    class Car {
      constructor(brand) {
        this.carname = brand;
      }
      present() {
        return 'I have a ' + this.carname;
      }
    }

    class Model extends Car {
      constructor(brand, mod) {
        super(brand);
        this.model = mod;
      }
      show() {
        return this.present() + ', it is a ' + this.model;
      }
    }

    mycar = new Model("AUDI", "Q7");
    console.log(mycar.present());
    console.log(mycar)
  </script>

</body>
</html>

Output:

Using extends object

This example extends the built-in Date object.

<script>
    class myDate extends Date {

      getFormattedDate() {
        var months = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
        
        return this.getDate() + '-' + months[this.getMonth()] + '-' + this.getFullYear();
      }
    }

    var d = new myDate()
    console.log(d.getFormattedDate())

</script>

Output:

16-May-2022

Do comment if you have any doubts or suggestions on this JS extends keyword.

Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version

JavaScript extends | keyword