Reverse in place algorithm for arrays

reverseInPlace.js

function reverseInPlace(arr) {
  let length = arr.length,
  middle = Math.floor(length / 2),
  temp = null

  for(let i = 0; i < middle; i++) {
    temp = arr[i]
    arr[i] = arr[arr.length - 1 - i]
    arr[arr.length - 1 - i] = temp
  }
}

const arr1 = [-1, 0, 11, 9]
reverseInPlace(arr1)
console.log(arr1) // [9, 11, 0, -1]