why can "for in" use const in JS?

Question

const arr = [1, 2, 3]

for (let i = 0; i < arr.length; i++) { // can't use const
  console.log(i, arr[i]);
}

for (const i in arr) { // const is ok
  console.log(i, arr[i]);
}

Why can "for in" use const but "for" can't?

Answer 1

You can't use const in the first loop because of i++ which will reassign the variable i.

In the for in loop, i can be a const because it is defined for each iteration.

Answer 2

in the const element in arr the element is the same as element in the const element = arr[i] in the classical forloop. It is a constant variable with local scope, so it is declared and destroyed in each iteration.