add polyfill.coffee

lib/polyfill.coffee

@@ -0,0 +1,22 @@
+Polyfill =
+  init: ->
+    Polyfill.visibility()
+  visibility: ->
+    # page visibility API
+    return if 'visibilityState' of document
+    if 'webkitVisibilityState' of document
+      prefix = 'webkit'
+    else if 'mozVisibilityState' of document
+      prefix = 'moz'
+    else
+      return
+
+    property = prefix + 'VisibilityState'
+    event    = prefix + 'visibilitychange'
+
+    d.visibilityState = d[property]
+    d.hidden = d.visibilityState is 'hidden'
+    $.on d, event, ->
+      d.visibilityState = d[property]
+      d.hidden = d.visibilityState is 'hidden'
+      $.event 'visibilitychange'