feat(Viewer): add #off to remove event listeners

Closes #470

lib/Viewer.js

@@ -25,7 +25,7 @@ function initListeners(diagram, listeners) {
   var events = diagram.get('eventBus');
 
   listeners.forEach(function(l) {
-    events.on(l.event, l.priority, l.handler, l.that);
+    events.on(l.event, l.priority, l.callback, l.that);
   });
 }
 
@@ -365,17 +365,54 @@ Viewer.prototype.destroy = function() {
 /**
  * Register an event listener on the viewer
  *
+ * Remove a previously added listener via {@link #off(event, callback)}.
+ * 
  * @param {String} event
- * @param {Function} handler
+ * @param {Number} [priority]
+ * @param {Function} callback
+ * @param {Object} [that]
  */
-Viewer.prototype.on = function(event, priority, handler, that) {
+Viewer.prototype.on = function(event, priority, callback, that) {
   var diagram = this.diagram,
       listeners = this.__listeners = this.__listeners || [];
 
-  listeners.push({ event: event, priority: priority, handler: handler, that: that });
+  if (typeof priority === 'function') {
+    that = callback;
+    callback = priority;
+    priority = 1000;
+  }
+  
+  listeners.push({ event: event, priority: priority, callback: callback, that: that });
 
   if (diagram) {
-    diagram.get('eventBus').on(event, priority, handler, that);
+    return diagram.get('eventBus').on(event, priority, callback, that);
+  }
+};
+
+/**
+ * De-register an event callback
+ *
+ * @param {String} event
+ * @param {Function} callback
+ */
+Viewer.prototype.off = function(event, callback) {
+  var filter,
+      diagram = this.diagram;
+  
+  if (callback) {
+    filter = function(l) {
+      return !(l.event === event && l.callback === callback);
+    };
+  } else {
+    filter = function(l) {
+      return l.event !== event;
+    };
+  }
+  
+  this.__listeners = (this.__listeners || []).filter(filter);
+  
+  if (diagram) {
+    diagram.get('eventBus').off(event, callback);
   }
 };
 

test/spec/ViewerSpec.js

@@ -626,6 +626,68 @@ describe('Viewer', function() {
   });
 
 
+  describe.only('#off', function() {
+    
+    var xml = require('../fixtures/bpmn/simple.bpmn');
+    
+    it('should remove listener permanently', function(done) {
+
+      // given
+      var viewer = new Viewer({ container: container });
+
+      var handler = function() {
+        return 'bar';
+      };
+      
+      viewer.on('foo', 1000, handler);
+
+      // when
+      viewer.off('foo');
+      
+      // then
+      viewer.importXML(xml, function(err) {
+        var eventBus = viewer.get('eventBus');
+
+        var result = eventBus.fire('foo');
+
+        expect(result).not.to.exist;
+
+        done();
+      });
+
+    });
+    
+    
+    it('should remove listener on existing diagram instance', function(done) {
+
+      // given
+      var viewer = new Viewer({ container: container });
+
+      var handler = function() {
+        return 'bar';
+      };
+      
+      viewer.on('foo', 1000, handler);
+      
+      // when
+      viewer.importXML(xml, function(err) {
+        var eventBus = viewer.get('eventBus');
+        
+        // when
+        viewer.off('foo', handler);
+        
+        var result = eventBus.fire('foo');
+
+        expect(result).not.to.exist;
+
+        done();
+      });
+
+    });
+
+  });
+  
+  
   describe('#destroy', function() {
 
     it('should remove traces in document tree', function() {