[Javascript] MetaProgramming: new.target

new.target is a new “magical” value available in all functions, thoughin normal functions it will always be undefined. In any constructor,new.target always points at the constructor that new actuallydirectly invoked.

class Parent {

    constructor() {

        if (new.target === Parent) {

            console.log( "Parent instantiated" );

        }

        else {

            console.log( "A child instantiated" );

        }

    }

}

class Child extends Parent {}

var a = new Parent();

// Parent instantiated

var b = new Child(); // here new.target is undefined

// A child instantiated

When the class is extended, it will show undefined in the parent class construcotr().