difference between var let and const in javascript with example

1The difference is that with const you can only only assign a value to a variable
2once, but with let it allows you to reassign after it has been assigned.

1//functional scope 
2 var a; // declaration
3 a=10; // initialization; 
4//global scope
5// re-initialization possible
6 let a;//only blocked scope & re-initialization possible
7 a=10;
8let a =20;
9if(true){
10  let b =30;
11}
12console.log(b); // b is not defined
13const // const also blocked scope,Re-initialization and re-declaration not possible
14const a; // throws error {when we declaring the value we should assign the value.
15const a =20;
16if(true){
17  const b =30;
18}
19console.log(b); // b is not defined
20console.log(a); // no output here because code execution break at leve b.
21