The Difference between Var, Let & Const

Variables are containers for storing data or values. A variable must have a unique name.

There are three ways that we can declare a variable, we can declare with Var, Let or Const.

JavaScript uses reserved keyword var to declare a variable, var is function scoped and a global variable which is accessible anywhere with in our program and it can be re-assigned, re-defined and can be hoisted.

e.g:-

var counter = 0

counter = 1

=> 1

One of the features that came with ECMAScript 6(ES6) is the addition of let and const, which can be used for variable declaration.

let is a Local Variable and it is block scoped and just like var it can be re-assigned but cannot be re-defined or hoisted.

e.g:-

let counter = 0

counter = 1

=> 1

const Is also a local variable and block scoped however unlike var and let, const cannot be re-assigned it also cannot be re-defined and hoisted.

e.g:-

const name = “pat”

name

=> “pat”

name = “bet”

*** Uncaught TypeError: Assignment to constant variable.***

N:B:- It is strongly advisable to use let and const over var as var is considered as a bad practice.