Implement event dispatcher

Author: janodvarko

data/dispatcher.js

@@ -0,0 +1,70 @@
+/* See license.txt for terms of usage */
+
+define(function(require, exports, module) {
+
+var listeners = {};
+
+/**
+ * The application event emitter.
+ */
+var Dispatcher =
+/** @lends Dispatcher */
+{
+  on: function(type, listener) {
+    var listeners = observers(type);
+    listeners.push(listener);
+  },
+
+  off: function(type, listener) {
+    var listeners = observers(type);
+    var index = listeners.indexOf(listener);
+    if (index >= 0) {
+      listeners.splice(index, 1);
+    }
+  },
+
+  once: function(type, listener) {
+    var self = this;
+    this.on(type, function observer(args) {
+      self.off(type, observer);
+      try {
+        listener.apply(self, args);
+      } catch (err) {
+        Trace.sysout("Dispatcher.once; EXCEPTION " + err, err);
+      }
+    });
+  },
+
+  dispatch: function(type, args) {
+    var results = [];
+
+    var listeners = observers(type);
+    for (var i=0; i<listeners.length; i++) {
+      try {
+        var listener = listeners[i];
+        var result = listener(args);
+
+        // Store all valid results into the result array. The only invalid
+        // type is undefined (null, 0 can be treated as valid results in some
+        // cases).
+        if (typeof result != "undefined") {
+          results.push(result);
+        }
+      } catch (err) {
+        Trace.sysout("Dispatcher.emit; EXCEPTION " + err, err);
+      }
+    }
+
+    return results;
+  },
+};
+
+// Helpers
+
+function observers(type) {
+  return type in listeners ? listeners[type] : listeners[type] = [];
+}
+
+// Exports from this module
+exports.Dispatcher = Dispatcher;
+});