diff --git a/examples/device-orientation.js b/examples/device-orientation.js
index b464d2e958..318dc6468d 100644
--- a/examples/device-orientation.js
+++ b/examples/device-orientation.js
@@ -25,11 +25,13 @@ var deviceOrientation = new ol.DeviceOrientation();
 var track = new ol.dom.Input(document.getElementById('track'));
 track.bindTo('checked', deviceOrientation, 'tracking');
 
-deviceOrientation.on('change', function(event) {
-  document.getElementById('alpha').innerHTML = event.target.getAlpha();
-  document.getElementById('beta').innerHTML = event.target.getBeta();
-  document.getElementById('gamma').innerHTML = event.target.getGamma();
-  document.getElementById('heading').innerHTML = event.target.getHeading();
+deviceOrientation.on('propertychange', function(event) {
+  // event.getKey() is the changed property name
+  var key = event.getKey();
+  var element = document.getElementById(key);
+  if (element) {
+    element.innerHTML = deviceOrientation.get(key);
+  }
 });
 
 // tilt the map
diff --git a/examples/geolocation.js b/examples/geolocation.js
index 7fb3fe83f2..fc0d2ac62e 100644
--- a/examples/geolocation.js
+++ b/examples/geolocation.js
@@ -29,7 +29,7 @@ geolocation.bindTo('projection', map.getView());
 var track = new ol.dom.Input(document.getElementById('track'));
 track.bindTo('checked', geolocation, 'tracking');
 
-geolocation.on('change', function() {
+geolocation.on('propertychange', function() {
   $('#accuracy').text(geolocation.getAccuracy() + ' [m]');
   $('#altitude').text(geolocation.getAltitude() + ' [m]');
   $('#altitudeAccuracy').text(geolocation.getAltitudeAccuracy() + ' [m]');
diff --git a/src/ol/layer/layergroup.js b/src/ol/layer/layergroup.js
index 50649459f0..4e00e74c5d 100644
--- a/src/ol/layer/layergroup.js
+++ b/src/ol/layer/layergroup.js
@@ -10,6 +10,7 @@ goog.require('ol.Collection');
 goog.require('ol.CollectionEvent');
 goog.require('ol.CollectionEventType');
 goog.require('ol.Object');
+goog.require('ol.ObjectEventType');
 goog.require('ol.layer.Base');
 goog.require('ol.source.State');
 
@@ -104,7 +105,8 @@ ol.layer.Group.prototype.handleLayersChanged_ = function(event) {
     for (i = 0, ii = layersArray.length; i < ii; i++) {
       layer = layersArray[i];
       this.listenerKeys_[goog.getUid(layer).toString()] =
-          goog.events.listen(layer, goog.events.EventType.CHANGE,
+          goog.events.listen(layer,
+              [ol.ObjectEventType.PROPERTYCHANGE, goog.events.EventType.CHANGE],
               this.handleLayerChange_, false, this);
     }
   }
@@ -120,8 +122,8 @@ ol.layer.Group.prototype.handleLayersChanged_ = function(event) {
 ol.layer.Group.prototype.handleLayersAdd_ = function(collectionEvent) {
   var layer = /** @type {ol.layer.Base} */ (collectionEvent.getElement());
   this.listenerKeys_[goog.getUid(layer).toString()] = goog.events.listen(
-      layer, goog.events.EventType.CHANGE, this.handleLayerChange_, false,
-      this);
+      layer, [ol.ObjectEventType.PROPERTYCHANGE, goog.events.EventType.CHANGE],
+      this.handleLayerChange_, false, this);
   this.dispatchChangeEvent();
 };
 
diff --git a/src/ol/map.js b/src/ol/map.js
index 69fd635db6..7caf96bcc0 100644
--- a/src/ol/map.js
+++ b/src/ol/map.js
@@ -39,6 +39,7 @@ goog.require('ol.MapBrowserEventHandler');
 goog.require('ol.MapEvent');
 goog.require('ol.MapEventType');
 goog.require('ol.Object');
+goog.require('ol.ObjectEvent');
 goog.require('ol.ObjectEventType');
 goog.require('ol.Pixel');
 goog.require('ol.PostRenderFunction');
@@ -208,9 +209,9 @@ ol.Map = function(options) {
 
   /**
    * @private
-   * @type {goog.events.Key}
+   * @type {Array.<goog.events.Key>}
    */
-  this.layerGroupPropertyListenerKey_ = null;
+  this.layerGroupPropertyListenerKeys_ = null;
 
   /**
    * @private
@@ -888,7 +889,7 @@ ol.Map.prototype.handleViewChanged_ = function() {
   var view = this.getView();
   if (goog.isDefAndNotNull(view)) {
     this.viewPropertyListenerKey_ = goog.events.listen(
-        view, ol.ObjectEventType.CHANGE,
+        view, ol.ObjectEventType.PROPERTYCHANGE,
         this.handleViewPropertyChanged_, false, this);
   }
   this.render();
@@ -899,7 +900,18 @@ ol.Map.prototype.handleViewChanged_ = function() {
  * @param {goog.events.Event} event Event.
  * @private
  */
+ol.Map.prototype.handleLayerGroupMemberChanged_ = function(event) {
+  goog.asserts.assertInstanceof(event, goog.events.Event);
+  this.render();
+};
+
+
+/**
+ * @param {ol.ObjectEvent} event Event.
+ * @private
+ */
 ol.Map.prototype.handleLayerGroupPropertyChanged_ = function(event) {
+  goog.asserts.assertInstanceof(event, ol.ObjectEvent);
   this.render();
 };
 
@@ -908,15 +920,23 @@ ol.Map.prototype.handleLayerGroupPropertyChanged_ = function(event) {
  * @private
  */
 ol.Map.prototype.handleLayerGroupChanged_ = function() {
-  if (!goog.isNull(this.layerGroupPropertyListenerKey_)) {
-    goog.events.unlistenByKey(this.layerGroupPropertyListenerKey_);
-    this.layerGroupPropertyListenerKey_ = null;
+  if (!goog.isNull(this.layerGroupPropertyListenerKeys_)) {
+    var length = this.layerGroupPropertyListenerKeys_.length;
+    for (var i = 0; i < length; ++i) {
+      goog.events.unlistenByKey(this.layerGroupPropertyListenerKeys_[i]);
+    }
+    this.layerGroupPropertyListenerKeys_ = null;
   }
   var layerGroup = this.getLayerGroup();
   if (goog.isDefAndNotNull(layerGroup)) {
-    this.layerGroupPropertyListenerKey_ = goog.events.listen(
-        layerGroup, ol.ObjectEventType.CHANGE,
-        this.handleLayerGroupPropertyChanged_, false, this);
+    this.layerGroupPropertyListenerKeys_ = [
+      goog.events.listen(
+          layerGroup, ol.ObjectEventType.PROPERTYCHANGE,
+          this.handleLayerGroupPropertyChanged_, false, this),
+      goog.events.listen(
+          layerGroup, goog.events.EventType.CHANGE,
+          this.handleLayerGroupMemberChanged_, false, this)
+    ];
   }
   this.render();
 };
diff --git a/src/ol/object.exports b/src/ol/object.exports
index 89426170a5..3b9b0d2900 100644
--- a/src/ol/object.exports
+++ b/src/ol/object.exports
@@ -7,3 +7,6 @@
 @exportProperty ol.Object.prototype.setValues
 @exportProperty ol.Object.prototype.unbind
 @exportProperty ol.Object.prototype.unbindAll
+
+@exportSymbol ol.ObjectEvent
+@exportProperty ol.ObjectEvent.prototype.getKey
diff --git a/src/ol/object.js b/src/ol/object.js
index 4bca4e75ca..a918f8df06 100644
--- a/src/ol/object.js
+++ b/src/ol/object.js
@@ -6,10 +6,12 @@
  */
 
 goog.provide('ol.Object');
+goog.provide('ol.ObjectEvent');
 goog.provide('ol.ObjectEventType');
 
 goog.require('goog.array');
 goog.require('goog.events');
+goog.require('goog.events.Event');
 goog.require('goog.functions');
 goog.require('goog.object');
 goog.require('ol.Observable');
@@ -19,7 +21,40 @@ goog.require('ol.Observable');
  * @enum {string}
  */
 ol.ObjectEventType = {
-  CHANGE: 'change'
+  BEFOREPROPERTYCHANGE: 'beforepropertychange',
+  PROPERTYCHANGE: 'propertychange'
+};
+
+
+
+/**
+ * Object representing a property change event.
+ *
+ * @param {string} type The event type.
+ * @param {string} key The property name.
+ * @extends {goog.events.Event}
+ * @constructor
+ */
+ol.ObjectEvent = function(type, key) {
+  goog.base(this, type);
+
+  /**
+   * The name of the property whose value is changing.
+   * @type {string}
+   * @private
+   */
+  this.key_ = key;
+
+};
+goog.inherits(ol.ObjectEvent, goog.events.Event);
+
+
+/**
+ * Get the name of the property associated with this event.
+ * @return {string} Object property name.
+ */
+ol.ObjectEvent.prototype.getKey = function() {
+  return this.key_;
 };
 
 
@@ -94,6 +129,13 @@ ol.Object = function(opt_values) {
    */
   this.values_ = {};
 
+  /**
+   * Lookup of beforechange listener keys.
+   * @type {Object.<string, goog.events.Key>}
+   * @private
+   */
+  this.beforeChangeListeners_ = {};
+
   if (goog.isDef(opt_values)) {
     this.setValues(opt_values);
   }
@@ -216,11 +258,20 @@ ol.Object.getSetterName = function(key) {
 ol.Object.prototype.bindTo = function(key, target, opt_targetKey) {
   var targetKey = opt_targetKey || key;
   this.unbind(key);
+
+  // listen for change:targetkey events
   var eventType = ol.Object.getChangeEventType(targetKey);
   var listeners = ol.Object.getListeners(this);
   listeners[key] = goog.events.listen(target, eventType, function() {
     this.notifyInternal_(key);
   }, undefined, this);
+
+  // listen for beforechange events and relay if key matches
+  this.beforeChangeListeners_[key] = goog.events.listen(target,
+      ol.ObjectEventType.BEFOREPROPERTYCHANGE,
+      this.createBeforeChangeListener_(key, targetKey),
+      undefined, this);
+
   var accessor = new ol.ObjectAccessor(target, targetKey);
   var accessors = ol.Object.getAccessors(this);
   accessors[key] = accessor;
@@ -229,6 +280,30 @@ ol.Object.prototype.bindTo = function(key, target, opt_targetKey) {
 };
 
 
+/**
+ * Create a listener for beforechange events on a target object.  This listener
+ * will relay events on this object if the event key matches the provided target
+ * key.
+ * @param {string} key The key on this object whose value will be changing.
+ * @param {string} targetKey The key on the target object.
+ * @return {function(this: ol.Object, ol.ObjectEvent)} Listener.
+ * @private
+ */
+ol.Object.prototype.createBeforeChangeListener_ = function(key, targetKey) {
+  /**
+   * Conditionally relay beforechange events if event key matches target key.
+   * @param {ol.ObjectEvent} event The beforechange event from the target.
+   * @this {ol.Object}
+   */
+  return function(event) {
+    if (event.getKey() === targetKey) {
+      this.dispatchEvent(
+          new ol.ObjectEvent(ol.ObjectEventType.BEFOREPROPERTYCHANGE, key));
+    }
+  };
+};
+
+
 /**
  * Gets a value.
  * @param {string} key Key name.
@@ -331,7 +406,8 @@ ol.Object.prototype.notify = function(key) {
 ol.Object.prototype.notifyInternal_ = function(key) {
   var eventType = ol.Object.getChangeEventType(key);
   this.dispatchEvent(eventType);
-  this.dispatchEvent(ol.ObjectEventType.CHANGE);
+  this.dispatchEvent(
+      new ol.ObjectEvent(ol.ObjectEventType.PROPERTYCHANGE, key));
 };
 
 
@@ -342,6 +418,8 @@ ol.Object.prototype.notifyInternal_ = function(key) {
  * @todo stability experimental
  */
 ol.Object.prototype.set = function(key, value) {
+  this.dispatchEvent(
+      new ol.ObjectEvent(ol.ObjectEventType.BEFOREPROPERTYCHANGE, key));
   var accessors = ol.Object.getAccessors(this);
   if (accessors.hasOwnProperty(key)) {
     var accessor = accessors[key];
@@ -397,6 +475,13 @@ ol.Object.prototype.unbind = function(key) {
     delete accessors[key];
     this.values_[key] = value;
   }
+
+  // unregister any beforechange listener
+  var listenerKey = this.beforeChangeListeners_[key];
+  if (listenerKey) {
+    goog.events.unlistenByKey(listenerKey);
+    delete this.beforeChangeListeners_[key];
+  }
 };
 
 
diff --git a/test/spec/ol/layer/layer.test.js b/test/spec/ol/layer/layer.test.js
index 8fd23001e3..4d8f1b516c 100644
--- a/test/spec/ol/layer/layer.test.js
+++ b/test/spec/ol/layer/layer.test.js
@@ -212,7 +212,7 @@ describe('ol.layer.Layer', function() {
 
     it('triggers a change event', function() {
       var listener = sinon.spy();
-      layer.on(ol.ObjectEventType.CHANGE, listener);
+      layer.on(ol.ObjectEventType.PROPERTYCHANGE, listener);
       layer.setBrightness(0.5);
       expect(listener.calledOnce).to.be(true);
     });
@@ -247,7 +247,7 @@ describe('ol.layer.Layer', function() {
 
     it('triggers a change event', function() {
       var listener = sinon.spy();
-      layer.on(ol.ObjectEventType.CHANGE, listener);
+      layer.on(ol.ObjectEventType.PROPERTYCHANGE, listener);
       layer.setContrast(43);
       expect(listener.calledOnce).to.be(true);
     });
@@ -293,7 +293,7 @@ describe('ol.layer.Layer', function() {
 
     it('triggers a change event', function() {
       var listener = sinon.spy();
-      layer.on(ol.ObjectEventType.CHANGE, listener);
+      layer.on(ol.ObjectEventType.PROPERTYCHANGE, listener);
       layer.setHue(0.5);
       expect(listener.calledOnce).to.be(true);
     });
@@ -324,7 +324,7 @@ describe('ol.layer.Layer', function() {
 
     it('triggers a change event', function() {
       var listener = sinon.spy();
-      layer.on(ol.ObjectEventType.CHANGE, listener);
+      layer.on(ol.ObjectEventType.PROPERTYCHANGE, listener);
       layer.setOpacity(0.4);
       expect(listener.calledOnce).to.be(true);
     });
@@ -360,7 +360,7 @@ describe('ol.layer.Layer', function() {
 
     it('triggers a change event', function() {
       var listener = sinon.spy();
-      layer.on(ol.ObjectEventType.CHANGE, listener);
+      layer.on(ol.ObjectEventType.PROPERTYCHANGE, listener);
       layer.setSaturation(42);
       expect(listener.calledOnce).to.be(true);
     });
@@ -393,7 +393,7 @@ describe('ol.layer.Layer', function() {
 
     it('fires a change event', function() {
       var listener = sinon.spy();
-      layer.on(ol.ObjectEventType.CHANGE, listener);
+      layer.on(ol.ObjectEventType.PROPERTYCHANGE, listener);
 
       layer.setVisible(false);
       expect(listener.callCount).to.be(1);
diff --git a/test/spec/ol/layer/layergroup.test.js b/test/spec/ol/layer/layergroup.test.js
index cefa283374..d3a29cfd15 100644
--- a/test/spec/ol/layer/layergroup.test.js
+++ b/test/spec/ol/layer/layergroup.test.js
@@ -63,7 +63,7 @@ describe('ol.layer.Group', function() {
 
   });
 
-  describe('change event', function() {
+  describe('generic change event', function() {
 
     var layer, group, listener;
     beforeEach(function() {
@@ -84,14 +84,14 @@ describe('ol.layer.Group', function() {
     });
 
     it('is dispatched by the group when layer opacity changes', function() {
-      group.on(ol.ObjectEventType.CHANGE, listener);
+      group.on(goog.events.EventType.CHANGE, listener);
 
       layer.setOpacity(0.5);
       expect(listener.calledOnce).to.be(true);
     });
 
     it('is dispatched by the group when layer visibility changes', function() {
-      group.on(ol.ObjectEventType.CHANGE, listener);
+      group.on(goog.events.EventType.CHANGE, listener);
 
       layer.setVisible(false);
       expect(listener.callCount).to.be(1);
@@ -102,6 +102,45 @@ describe('ol.layer.Group', function() {
 
   });
 
+  describe('property change event', function() {
+
+    var layer, group, listener;
+    beforeEach(function() {
+      layer = new ol.layer.Layer({
+        source: new ol.source.Source({
+          projection: 'EPSG:4326'
+        })
+      });
+      group = new ol.layer.Group({
+        layers: [layer]
+      });
+      listener = sinon.spy();
+    });
+
+    afterEach(function() {
+      goog.dispose(group);
+      goog.dispose(layer);
+    });
+
+    it('is dispatched by the group when group opacity changes', function() {
+      group.on(ol.ObjectEventType.PROPERTYCHANGE, listener);
+
+      group.setOpacity(0.5);
+      expect(listener.calledOnce).to.be(true);
+    });
+
+    it('is dispatched by the group when group visibility changes', function() {
+      group.on(ol.ObjectEventType.PROPERTYCHANGE, listener);
+
+      group.setVisible(false);
+      expect(listener.callCount).to.be(1);
+
+      group.setVisible(true);
+      expect(listener.callCount).to.be(2);
+    });
+
+  });
+
   describe('constructor (options)', function() {
 
     it('accepts options', function() {
@@ -352,6 +391,7 @@ describe('ol.layer.Group', function() {
 });
 
 goog.require('goog.dispose');
+goog.require('goog.events.EventType');
 goog.require('ol.ObjectEventType');
 goog.require('ol.layer.Layer');
 goog.require('ol.layer.Group');
diff --git a/test/spec/ol/object.test.js b/test/spec/ol/object.test.js
index 1c59d6f273..f82bb37a9e 100644
--- a/test/spec/ol/object.test.js
+++ b/test/spec/ol/object.test.js
@@ -106,7 +106,7 @@ describe('ol.Object', function() {
       goog.events.listen(o, 'change:k', listener1);
 
       listener2 = sinon.spy();
-      goog.events.listen(o, 'change', listener2);
+      goog.events.listen(o, ol.ObjectEventType.PROPERTYCHANGE, listener2);
 
       var o2 = new ol.Object();
       o2.bindTo('k', o);
@@ -121,7 +121,11 @@ describe('ol.Object', function() {
 
     it('dispatches generic change events to bound objects', function() {
       o.notify('k');
-      expect(listener2).to.be.called();
+      expect(listener2.calledOnce).to.be(true);
+      var args = listener2.firstCall.args;
+      expect(args).to.have.length(1);
+      var event = args[0];
+      expect(event.getKey()).to.be('k');
     });
 
     it('dispatches events to bound objects', function() {
@@ -139,7 +143,7 @@ describe('ol.Object', function() {
       goog.events.listen(o, 'change:k', listener1);
 
       listener2 = sinon.spy();
-      goog.events.listen(o, 'change', listener2);
+      goog.events.listen(o, ol.ObjectEventType.PROPERTYCHANGE, listener2);
 
       o2 = new ol.Object();
       o2.bindTo('k', o);
@@ -157,7 +161,25 @@ describe('ol.Object', function() {
 
     it('dispatches generic change events to object', function() {
       o.set('k', 1);
-      expect(listener2).to.be.called();
+      expect(listener2.calledOnce).to.be(true);
+      var args = listener2.firstCall.args;
+      expect(args).to.have.length(1);
+      var event = args[0];
+      expect(event.getKey()).to.be('k');
+    });
+
+    it('dispatches beforechange events to object', function() {
+      o.set('k', 1);
+
+      var oldValue;
+      var beforeListener = sinon.spy(function(event) {
+        oldValue = o2.get(event.getKey());
+      });
+      o.on(ol.ObjectEventType.BEFOREPROPERTYCHANGE, beforeListener);
+
+      o.set('k', 2);
+      expect(beforeListener.calledOnce).to.be(true);
+      expect(oldValue).to.be(1);
     });
 
     it('dispatches events to bound object', function() {
@@ -175,8 +197,80 @@ describe('ol.Object', function() {
 
     it('dispatches generic change events to object bound to', function() {
       o2.set('k', 2);
-      expect(listener2).to.be.called();
+      expect(listener2.calledOnce).to.be(true);
+      var args = listener2.firstCall.args;
+      expect(args).to.have.length(1);
+      var event = args[0];
+      expect(event.getKey()).to.be('k');
     });
+
+    it('dispatches beforechange before changing bound objects', function() {
+      o2.set('k', 1);
+
+      var oldValue;
+      var beforeListener = sinon.spy(function(event) {
+        oldValue = o2.get(event.getKey());
+      });
+      o.on(ol.ObjectEventType.BEFOREPROPERTYCHANGE, beforeListener);
+
+      o2.set('k', 2);
+      expect(beforeListener.calledOnce).to.be(true);
+      var args = beforeListener.firstCall.args;
+      expect(args).to.have.length(1);
+      var event = args[0];
+      expect(event.getKey()).to.be('k');
+
+      expect(oldValue).to.be(1);
+    });
+
+    it('relays beforechange events from bound objects', function() {
+      var target = new ol.Object({
+        foo: 'original value'
+      });
+      var object = new ol.Object();
+      object.bindTo('foo', target);
+
+      var oldValue;
+      var beforeListener = sinon.spy(function(event) {
+        oldValue = object.get(event.getKey());
+      });
+      object.on(ol.ObjectEventType.BEFOREPROPERTYCHANGE, beforeListener);
+
+      target.set('foo', 'new value');
+      expect(beforeListener.calledOnce).to.be(true);
+      var args = beforeListener.firstCall.args;
+      expect(args).to.have.length(1);
+      var event = args[0];
+      expect(event.getKey()).to.be('foo');
+
+      expect(oldValue).to.be('original value');
+      expect(object.get('foo')).to.be('new value');
+    });
+
+    it('relays beforechange events when bound with a new key', function() {
+      var target = new ol.Object({
+        foo: 'original value'
+      });
+      var object = new ol.Object();
+      object.bindTo('bar', target, 'foo');
+
+      var oldValue;
+      var beforeListener = sinon.spy(function(event) {
+        oldValue = object.get(event.getKey());
+      });
+      object.on(ol.ObjectEventType.BEFOREPROPERTYCHANGE, beforeListener);
+
+      target.set('foo', 'new value');
+      expect(beforeListener.calledOnce).to.be(true);
+      var args = beforeListener.firstCall.args;
+      expect(args).to.have.length(1);
+      var event = args[0];
+      expect(event.getKey()).to.be('bar');
+
+      expect(oldValue).to.be('original value');
+      expect(object.get('bar')).to.be('new value');
+    });
+
   });
 
   describe('bind', function() {
@@ -256,6 +350,59 @@ describe('ol.Object', function() {
       expect(o.get('k')).to.eql(1);
       expect(o2.get('k')).to.eql(2);
     });
+
+    it('stops relaying beforechange events', function() {
+      var target = new ol.Object({
+        foo: 'original value'
+      });
+      var object = new ol.Object();
+      object.bindTo('foo', target);
+
+      var listener = sinon.spy();
+      object.on(ol.ObjectEventType.BEFOREPROPERTYCHANGE, listener);
+
+      target.set('foo', 'new value');
+      expect(listener.calledOnce).to.be(true);
+      var call = listener.firstCall;
+      expect(call.args).to.have.length(1);
+      expect(call.args[0].getKey()).to.be('foo');
+
+      object.unbind('foo');
+      target.set('foo', 'another new value');
+      expect(listener.calledOnce).to.be(true);
+
+      expect(object.get('foo')).to.be('new value');
+    });
+
+    it('selectively stops relaying beforechange events', function() {
+      var target = new ol.Object({
+        foo: 'original foo',
+        bar: 'original bar'
+      });
+      var object = new ol.Object();
+      object.bindTo('foo', target);
+      object.bindTo('bar', target);
+
+      var listener = sinon.spy();
+      object.on(ol.ObjectEventType.BEFOREPROPERTYCHANGE, listener);
+
+      target.set('foo', 'new foo');
+      expect(listener.calledOnce).to.be(true);
+
+      target.set('bar', 'new bar');
+      expect(listener.callCount).to.be(2);
+
+      object.unbind('foo');
+      target.set('foo', 'another new foo');
+      expect(listener.callCount).to.be(2);
+
+      target.set('bar', 'another new bar');
+      expect(listener.callCount).to.be(3);
+      var lastCall = listener.getCall(2);
+      expect(lastCall.args).to.have.length(1);
+      expect(lastCall.args[0].getKey()).to.be('bar');
+    });
+
   });
 
   describe('unbindAll', function() {
@@ -567,3 +714,4 @@ describe('ol.Object', function() {
 
 goog.require('goog.events');
 goog.require('ol.Object');
+goog.require('ol.ObjectEventType');