Explain window and this keyword.

window

The global object of the browser environment.

Examples:

window.document
window.location
window.history
window.setTimeout

this

In a regular function it depends mainly on how the function is called.

const user = {
  name: "Tom",

  hello() {
    console.log(this.name);
  }
};

user.hello();

Here:

this === user

An arrow function doesn't create its own this.

It takes this from the surrounding lexical scope.