What Is Var, Let, And Const Keyword In Javascript

vat, let, and const keyword in JavaScript and its difference.

In JavaScript, developers can declare a variable using 3 keywords.

1. var
2. let
3. const

1. var 

• It is the oldest way to declare a variable.
• Using the var keyword we can re-assign the value to the variable.
• Declaring a variable name with the same name is also allowed.
• The scope of the var keyword is global/function scope.
• It can be accessed without initialization as its default value is “undefined”.

var myname='xxx';
console.log(myname); // xxx
var myname='yyy'; // yyy
console.log(myname);

2. let

• Re-assigning is allowed.
• But, declaring a variable with the same name is not allowed.
• The scope of the let keyword is block scope.
• It cannot be accessed without initialization, as it returns an error.    

let yourName='xxx';
console.log(yourName); // xxx
let yourName='yyy'; // Error
yourName = 'zzz' // zzz
console.log(yourName);

3. const

• Re-assigning is not allowed.
• Cannot be declared without initialization.
• Declaring a variable name with the same is also not allowed.
• The scope of the const keyword is also block scope.
• It cannot be accessed without initialization, as it cannot be declared without initialization.

const testName;  // Error 
const testNames = 'xyz';
const testNames = 'zyx'; // Error
testNames = 'zyxx'; // Error