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April 16, 2022 04:46 am GMT

What is this?

In JavaScript, the this keyword operates a little differently than in other languages. There are also some distinctions between stringent and non-strict modes.
The this keyword refers to different objects depending on how it is used:

  • In an object method, this refers to the object.

  • Alone, this refers to the global object.

  • In a function, this refers to the global object.

  • In a function, in strict mode, this is undefined.

  • In an event, this refers to the element that received the event.

this in a Method:
When used in an object method, this refers to the object.

const person = {  firstName: "John",  lastName: "Doe",  id: 5566,  fullName : function() {    return this.firstName + " " + this.lastName;  }};console.log(person.fullName()) //output : John Doe

this Alone:
When used alone, this refers to the global object.
Because this is running in the global scope.
In a browser window the global object is [object Window]

let x = this;console.log(x) //output is :[object Window]

In strict mode, when used alone, this also refers to the global object:

"use strict:";let x = this;console.log(x) //output is :[object Window]

this in a Function(Default):
In a function, the global object is the default binding for this.
In a browser window the global object is [object Window]:

function myFunction() {  return this;}myFunction() //output is : [object Window]

this in a Function (Strict):
JavaScript strict mode does not allow default binding.
So, when used in a function, in strict mode, this is undefined.

"use strict";function myFunction() {  return this;}myFunction() //output is : undefined

this in Event Handlers:
In HTML event handlers, this refers to the HTML element that received the event:

<button onclick="this.style.display='none'">  Click to Remove Me!</button>

Original Link: https://dev.to/bilalniaz15/what-is-this-57d6

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