Speedy Loops

example.js

var arr = ['apple', 'banana', 'cheese', 'donut', 'egg', 'fish'];

var send = function (item) {
  $.ajax({
    type: 'post',
    dataType: 'json',
    url: '/Foods/Consume',
    data: { food: item }
  });
};

// Normal for loop:

for (var i = 0, len = arr.length; i < len; i++) {
  send(arr[i]);
}

// Faster reverse while loop:

var i = arr.length;

while (i--) {
  send(arr[i]);
}

while is not required, you can use:

for (var i = arr.length; i--; ) {
  send(arr[i]);
}

If you plan on using the iterated instance multiple times, you can make this even faster by only once initializing the variant:

for (var i = arr.length, item; item = arr[i--], i; ) {
  // do a lot more stuff with item
  send(item);
}

If there are only truthish elements in your loop, you can even save 2 bytes:

for (var i = arr.length, item; item = arr[i--]; ) {
  // do a lot more stuff with item
  send(item);
}

Understood, but the purpose of this post is to note that the reverse while is the fastest performing JS loop: http://blogs.oracle.com/greimer/entry/best_way_to_code_a

I would guess the for loop in reverse being slower than the while loop in reverse is due to the testing conditions, which are rather unprecise.