theprojectsomething · March 17, 2014 07:26 · Mar 17, 2014
diff --git a/Timer.js b/Timer.js
@@ -0,0 +1,64 @@
+/*
+  Timer
+    - utilises animation frames (with a fallback to setTimeout when using the polyfill, below)
+    - returns remaining (or running) time
+    - pass a callback [fn], with an optional duration [ms] and autotart [bool], to the constructor or 'init' method
+      eg. new Timer(foo, 1000) *or* (new Timer()).init(foo, 0, true)
+    - for uniform x-browser support combine with the requestAnimationFrame polyfill from Erik Möller, et. al.
+      [https://github.com/darius/requestAnimationFrame]
+*/
+
+var Timer = function () {
+  var start, time, duration, callback, timer = this;
+
+  function tick () {
+    if(start===false) return;
+    time = time + now() - start;
+    timer.stop();
+    callback.call(timer, timer.time());
+    timer.start();
+  }
+
+  function now () {
+    return window.performance ? window.performance.now() : Date.now();
+  }
+
+  this.init = function (callback, duration /* milliseconds */, autostart) {
+    timer.callback(callback);
+    timer.duration(duration);
+    timer.reset();
+    if(autostart) timer.start();
+  };
+
+  this.start = function (reset /* true to restart */) {
+    if(reset) timer.reset(true);
+    if(!callback || start || time > duration) return;
+    start = now();
+    requestAnimationFrame(tick);
+  };
+
+  this.stop = function () {
+    start = false;
+  };
+
+  this.reset = function (stop) {
+    if(stop) timer.stop();
+    time = 0;
+  };
+
+  this.duration = function (ms) {
+    if(ms) duration = ms;
+    return duration;
+  };
+
+  this.callback = function (fn) {
+    if(typeof fn === "function") callback = fn;
+    return fn;
+  };
+
+  this.time = function (elapsed /* true for elapsed instead of remaining */) {
+    return !!elapsed || !duration  ? time : Math.max(0, duration - time);
+  };
+
+  if(arguments.length) this.init.apply(this, arguments);
+};