A function to reverse a list (loop: n/2, space: n).

reverse.js

var reverse = function (a) {
  for (var i=0, arrayLen=a.length ; i<arrayLen/2; i+=1) {
    var temp = a[arrayLen-i-1];
    a[arrayLen-i-1] = a[i];
    a[i] = temp;
  }
  return a;
};