Skip to main content

this keyword in javascript

Welcome file

this keyword is used to point at the current object in the code.
For instance: If the code is presently at an object created by the help of the ‘new’ keyword, then ‘this’ keyword will point to the object being created.

It has different values depending on where it is used:

  • In a method, this refers to the owner object.
  • Alone, this refers to the global object.
  • In strict mode this refer to the global object.
  • In a function, this refers to the global object.
  • In a function, in strict mode, this is undefined.

In an object method, this refers to the current object.
In the example, this refers to the employee object.

this keyword

this Alone

when this keyword is used alone, not written inside a function or object then it will refer to global object. & In browser window global object will be [object window]
In a browser window the Global object is [object Window]:

var x = this;  

this in a Function (Default)

In a JavaScript function, the owner of the function is the default binding for this.
So, in a function, this refers to the Global object [object Window].

function empFunction() {
return  this;
}

this in Strict mode

In strict mode this also refers to the Global object [object Window]:

Example

"use strict";  
var x = this;

this in a Function (Strict)

in JavaScript strict mode does not allow default binding.
So, when used in a function, in strict mode, this is undefined.

Example

"use strict";  
function empFunction() {  
return this;  
}

Comments

Popular

JavaScript type hoisting with variable function Expression

JavaScript type hoisting with variable function Expression Hoisting is JavaScript default behavior to moving declaration on the top. Variable can be used before its declaration. To understand this, first we need to understand of hoist meaning, hoist means “raise(something) by means of ropes & pulleys”. now we can relate hoisting with JavaScript. JavaScript interpreter moves all declaration on the top at runtime. It is best practice to declare all variable at the top of their respective scopes. , JavaScript is loosely syntax language so it will not throw any error at runtime if the variable used before its declaration. But JavaScript does not allow variable used before its declaration in “use strict” mode. Example 1 In this example, we can see in a normal scenario, when y has declared & then used. in this case, it will give output 10 as excepted. <p id= "demo" ></p> <script> var y; //Declare y y = 10 ; ...

JavaScript Closure

What is closure? It is my personal experience, I have never understood closure, I have read many articles & have seen many videos. Finally, I understood sometimes we even used a closure without realizing we were using a closure. First, understand the meaning of closure “an act or process of closing something”, now we can relate closure in javascript, closure is an inner function which wraps inside the outer function, which can access outer function scope & global function scope. for scoping you can read my previous blog:- http://uisource.blogspot.com/2018/08/javascript-variable-scoping.html why do we create? Global variables can be made local (private) with closures. To avoid the usage of global variables, use the local variables and wrap your code in the closure. A closure is an inner function that has access to the outer (enclosing) function’s variables—scope chain(Lexical scoping). The closure has three scope chains: it has access to its own scope (variables define...

JavaScript Variable Scoping

There are two types of variables in JavaScript.  Global variables have global access and are declared outside of any function. Local variables are those declared inside of function. Lexical Scoping(Nested JavaScript Function) means that in a nested group of functions, the inner functions have access to the variables and other resources of their parent scope. Global variable:- Global variable declares & initialize outside the function, & accessible in from anywhere in the code. The global variable always stored in memory even function execution finish, it always keeps in memory or always accessible from anywhere in the code. Example 1 var message= "hello i am global variable" ; //global variable function a (){ console.log(message); // output: hello i am global variable } function b (){ console.log(message); // output: hello i am global variable } function a() function b() In above example message is a global variab...