JavaScript ES6 Let

Here's a useful discussion related to the let function and a comparison with the usual var function.

_Let

The function let allows you to declare variables that are limited in scope to the block, statement, or expression on which it is used.
This is unlike the var keyword, which defines a variable globally or locally to an entire function regardless of block scope.

Scoping Rules

Variables declared by let have the block, in which they are defined, as their scope, as well as any contained subblocks.

_{SAMPLE CODE}

function varScope() {
  var num1 = 31;
  if (num1 % 2 == 1) {
    var num1 = 32;  // same variable, num.
    console.log(num1);  // 32
  }
  console.log(num1);  // 32
}

function letScope() {
  let num2 = 31;
  if (num2 % 2 == 1) {
    let num2 = 32;  // different variable, num.
    console.log(num2);  // 32
  }
  console.log(num2);  // 31
}

console.log("Output using varScope() :");
varScope();
console.log("");
console.log("Output using letScope() :");
letScope();

_OUTPUT

Output using varScope() :
32
32

Output using letScope() :
32
31

Errors with let

Redeclaring the same variable within the same function or block scope raises an Error.

_{SAMPLE CODE}

let a = 1;
let a = 2;

_OUTPUT

Identifier 'a' has already been declared

Task

We have declared a global variable index. Your task is to edit the given code so that the value of the global variable doesn't change.