README.md

Losing this

by Pawan Kumar @jsartisan

In JavaScript, the value of this can be "lost" when a method is passed as a callback or used separately from its object. This often happens with functions like setTimeout.

Consider the following code:

let user = {
  firstName: "John",
  sayHi() {
    alert(`Hello, ${this.firstName}!`);
  }
};

setTimeout(user.sayHi, 1000); // Hello, undefined!

Explain why the output of the above code is undefined instead of "John". Also, Explain what can we do to ensure that this inside sayHi refers to the user object, even when passed to setTimeout.