MokiD's comments

A while back I was programming for a naive but well-written JS interpreter for set top box apps, where map was generally being avoided because of performance.

I wrote quite a fast "map" (along with the others) that looked a bit like:

  exports.map = function fastMap (subject, fn, thisContext) {
    var i = subject.length,
        result = new Array(i);
    if (thisContext) {
      while (i--) {
        result[i] = fn.call(thisContext, subject[i], i, subject);
      }
    } else {
      while (i--) {
        result[i] = fn(subject[i], i, subject);
      }
    }
    return result;
  };

I'm not sure if I just used "result = []", but on modern browsers I think that'd be recommended. But yeah, if you're programming for a web browser then using another impl of map is probably going to be a waste of time.