add requestanimationframe polyfill

index.html

@@ -67,7 +67,8 @@ <h1 class="title">2048</h1>
     Created by <a href="http://gabrielecirulli.com" target="_blank">Gabriele Cirulli.</a> Based on <a href="https://itunes.apple.com/us/app/1024!/id823499224" target="_blank">1024 by Veewo Studio</a> and conceptually similar to <a href="http://asherv.com/threes/" target="_blank">Threes by Asher Vollmer.</a>
     </p>
   </div>
-
+
+  <script src="js/animframe_polyfill.js"></script>
   <script src="js/hammer.min.js"></script>
   <script src="js/keyboard_input_manager.js"></script>
   <script src="js/html_actuator.js"></script>

js/animframe_polyfill.js

@@ -0,0 +1,26 @@
+(function() {
+  var lastTime = 0;
+  var vendors = ['webkit', 'moz'];
+  for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
+    window.requestAnimationFrame = window[vendors[x]+'RequestAnimationFrame'];
+    window.cancelAnimationFrame =
+    window[vendors[x]+'CancelAnimationFrame'] || window[vendors[x]+'CancelRequestAnimationFrame'];
+  }
+
+  if (!window.requestAnimationFrame) {
+    window.requestAnimationFrame = function(callback, element) {
+      var currTime = new Date().getTime();
+      var timeToCall = Math.max(0, 16 - (currTime - lastTime));
+      var id = window.setTimeout(function() { callback(currTime + timeToCall); },
+      timeToCall);
+      lastTime = currTime + timeToCall;
+      return id;
+    };
+  }
+
+  if (!window.cancelAnimationFrame) {
+    window.cancelAnimationFrame = function(id) {
+      clearTimeout(id);
+    };
+  }
+}());