Difference between let , const and var in Javascript

In this blog, we will discuss the javascript keywords var, let and const.
After ES6 it's a bit confusing to understand this keyword and how they work inside the javascript.

Let's start the scope of let, var and const

Scope
let:- variables declared in let's are in the block scope

const:- variables declared in const are also in the block scope

var:- variable declared with var is in the functional scope

function abc () {
var a=10
}
console.log(a) // gives an error
for(let i = 0;i<2;i++){
    console.log( i ) // print 1 2 
}
console.log(i) // gives an error
{
const b=1;
console.log(b)// print 1
}
console.log(b)// gives an error

for var, it shows the error because its is functional scope so it cant accessible outside the function
for let inside the for loop block, it prints the output but outside the block, it gives an error as let is blocked scope
for const inside the curly braces, it prints the value but outside braces give an error as it is also a block scope

Let's check Reassigning values to let, const and var

var:- reassigning is allowed
let:- reassigning is allowed
const:- reassigning is not allowed

var a = 1 ;
a = 2;
console.log(a) // print 2
let l = 1; 
l = 2 ;
console.log(l) // print 2
const c = 1 ;
c=2
consol.log(c) // give an error

for var reassigning of value shows most recent value 2
for let also reassigning of value shows most recent value 2
for const reassigning of value gives an error as reassigning is not allowed

Let's check for Redeclaration of let, const and var

let:- Redeclaration is not allowed
var:- Redeclaration is allowed
const:- Redeclaration is not allowed

var v = 1;
var v = 20;
console.log(v);// prints 20
let i = 1;
let i = 20;
console.log(i); //  gives an error
const c = 1;
const c = 20;
console.log(c) // gives an error

for var, there is no error and prints the most recent declared value
for let and const there is an error as it does not allow the redeclaration of variable

These are some of the differences between let , const and var, hope you like it