es6-letConst.js

var value1 = 100;
let value2 = 100;
{
  var value1 = 200
  let value2 = 200  
}

console.log(value1); // 200
console.log(value2); // 100

const val3 = 22;
val3 = 24;           // error: val3 is read only
const val3 = 22;     // error: duplicate declaration