var
	arr = arr = Array(1000).fill().map((e,i)=>i),
	a = 5,
    b = 6;

function swap__old (arr, a, b) {
  var temp = arr[a];
  arr[a] = arr[b];
  arr[b] = temp;
  return arr;
}
function swap__es6 (arr, a, b) {
  [arr[a], arr[b]] = [arr[b], arr[a]];
}