requestAnimationFrame polyfill

rAF.js

// requestAnimationFrame polyfill by @rma4ok
!function (window) {
  var
      equestAnimationFrame = 'equestAnimationFrame',
      requestAnimationFrame = 'r' + equestAnimationFrame,

      ancelAnimationFrame = 'ancelAnimationFrame',
      cancelAnimationFrame = 'c' + ancelAnimationFrame,

      expectedTime = 0,
      vendors = ['moz', 'ms', 'o', 'webkit'],
      vendor;

  while (!window[requestAnimationFrame] && (vendor = vendors.pop())) {
    window[requestAnimationFrame] = window[vendor + 'R' + equestAnimationFrame];
    window[cancelAnimationFrame] =
        window[vendor + 'C' + ancelAnimationFrame] ||
            window[vendor + 'CancelR' + equestAnimationFrame];
  }

  if (!window[requestAnimationFrame]) {
    window[requestAnimationFrame] = function (callback) {
      var
          currentTime = +new Date,
          adjustedDelay = 16 - (currentTime - expectedTime),
          delay = adjustedDelay > 0 ? adjustedDelay : 0;

      expectedTime = currentTime + delay;

      return setTimeout(function () {
        callback(expectedTime);
      }, delay);
    };

    window[cancelAnimationFrame] = clearTimeout;
  }
}(this);

Mind helping me understand the reason behind this?

  equestAnimationFrame = 'equestAnimationFrame',
  requestAnimationFrame = 'r' + equestAnimationFrame,

looks odd :)

@wamatt for better minification i would say...

and why use !function in the first line? :)

@ddon calling an anonymous function the bang converts it to an expression from a function declaration.

Mhh, since +new Date is slower than (new Date).getTime(). I would recommend to use the latter. http://jsperf.com/date-now-vs-date-gettime/6

...and by the way, most modern browsers (i.e. IE9+) support Date.now() so we can use it and fallback to getTime().

@yckart , how it helps in minification, it's just variable reuse only

@arindamnayak

Since 'requestAnimationFrame' starts with capital 'R' in vendor-prefixed funtion names like 'webkitRequestAnimationFrame' and it is used multiple times, it's better to use in that way.