Add ol.Observable for on, once, un, and unByKey methods

src/ol/observable.js

@@ -0,0 +1,70 @@
+goog.provide('ol.Observable');
+
+goog.require('goog.events');
+goog.require('goog.events.EventTarget');
+
+
+
+/**
+ * An event target providing convenient methods for listener registration
+ * and unregistration.
+ * @constructor
+ * @extends {goog.events.EventTarget}
+ * @todo stability experimental
+ */
+ol.Observable = function() {
+  goog.base(this);
+
+};
+goog.inherits(ol.Observable, goog.events.EventTarget);
+
+
+/**
+ * Listen for a certain type of event.
+ * @param {string|Array.<string>} type The event type or array of event types.
+ * @param {function(?): ?} listener The listener function.
+ * @param {Object=} opt_scope Object is whose scope to call
+ *     the listener.
+ * @return {goog.events.Key} Unique key for the listener.
+ * @todo stability experimental
+ */
+ol.Observable.prototype.on = function(type, listener, opt_scope) {
+  return goog.events.listen(this, type, listener, false, opt_scope);
+};
+
+
+/**
+ * Listen once for a certain type of event.
+ * @param {string|Array.<string>} type The event type or array of event types.
+ * @param {function(?): ?} listener The listener function.
+ * @param {Object=} opt_scope Object is whose scope to call
+ *     the listener.
+ * @return {goog.events.Key} Unique key for the listener.
+ * @todo stability experimental
+ */
+ol.Observable.prototype.once = function(type, listener, opt_scope) {
+  return goog.events.listenOnce(this, type, listener, false, opt_scope);
+};
+
+
+/**
+ * Unlisten for a certain type of event.
+ * @param {string|Array.<string>} type The event type or array of event types.
+ * @param {function(?): ?} listener The listener function.
+ * @param {Object=} opt_scope Object is whose scope to call
+ *     the listener.
+ * @todo stability experimental
+ */
+ol.Observable.prototype.un = function(type, listener, opt_scope) {
+  goog.events.unlisten(this, type, listener, false, opt_scope);
+};
+
+
+/**
+ * Removes an event listener using the key returned by `on()` or `once()`.
+ * @param {goog.events.Key} key Key.
+ * @todo stability experimental
+ */
+ol.Observable.prototype.unByKey = function(key) {
+  goog.events.unlistenByKey(key);
+};