Advantages of using let over var within a function

Question

Say I have a piece of code like this:

const number = 3;

function fooFunction() {
  let numberTwo = 5;
  var answer = number + numberTwo;
  return answer;
}

finalAnswer = fooFunction();

console.log(finalAnswer);

Assuming an ES2015 compatible browser, what would be the advantages/disadvantages of using the above code, over:

const number = 3;

function fooFunction() {
  var numberTwo = 5;
  var answer = number + numberTwo;
  return answer;
}

finalAnswer = fooFunction();

console.log(finalAnswer);

Are there any advantages or disadvantages, given they both return the same number?

Answer 1

As others have mentioned, in your example you can use let and var interchangeably. The difference is that let is block-scoped and var is not.

For example with var you can do this (prints 'foo'):

function printFoo(param) {
  if (param) {
    var x = "foo";
  }

  console.log(x);
}

printFoo("hello");

You cannot do this with let because let x is scoped to the if block and therefore is not defined.