Var vs Let vs Const in JavaScript

In this topic we will learn:

var’ keyword.

Variable Hoisting

Problems with ‘var’ keyword

‘let’ keyword.

‘const’ keyword.

var vs let vs const

Scope

Scope decide where the variable is available for use. JavaScript have 3 Scopes:

•Global

•Function/Local

•Block

Before ES6 Edition, ‘var’ keyword ruled the variable declarations.

However, there are issues associated to variables declared with ‘var’.

•var is function scoped when it is declared within a function. This means that it is available and can be accessed only within that function.

• var variable declared outside a function have a global scope and is available to use in whole window.

var variables can be redeclared and updated

With ES6 edition new keywords let and constwere made available to declare variables.

A block is a chunk of code bounded by {}. Anything within curly braces is a block.

A variable declared in a block with let is only available for use within that block.

let can be updated but not re-declared.

let a better choice than var.

When using let, you don’t have to bother if you have used a name for a variable before as a variable exists only within its scope.

JavaScript const variables must be assigned a value when they are declared, and they maintain constant values.

A variable declared in a block with const is only available for use within that block

const cannot be updated or re-declared.

While a const object cannot be updated, the properties of this objects can be updated.

Please check below video for more detailed explaination on Var vs Let vs Const in JavaScript:

Let me know if you have any questions in the comment section of the video.