fix(Viewer): remove elements di binding on clear call

Closes #978

lib/Viewer.js

@@ -345,14 +345,6 @@ Viewer.prototype.saveSVG = function(options, done) {
  * @method Viewer#invoke
  */
 
-/**
- * Remove all drawn elements from the viewer.
- *
- * After calling this method the viewer can still
- * be reused for opening another diagram.
- *
- * @method Viewer#clear
- */
 
 Viewer.prototype.importDefinitions = function(definitions, done) {
 
@@ -377,6 +369,28 @@ Viewer.prototype.getModules = function() {
   return this._modules;
 };
 
+/**
+ * Remove all drawn elements from the viewer.
+ *
+ * After calling this method the viewer can still
+ * be reused for opening another diagram.
+ *
+ * @method Viewer#clear
+ */
+Viewer.prototype.clear = function() {
+  // (0) Remove elements di binding.
+  this.get('elementRegistry').forEach(function(element) {
+    var bo = element.businessObject;
+
+    if (bo && bo.di) {
+      delete bo.di;
+    }
+  });
+
+  // (1) Remove drawn elements.
+  Diagram.prototype.clear.call(this);
+};
+
 /**
  * Destroy the viewer instance and remove all its
  * remainders from the document tree.

test/spec/ViewerSpec.js

@@ -1082,6 +1082,48 @@ describe('Viewer', function() {
   });
 
 
+  describe('#clear', function() {
+
+    it('should not throw if diagram is already empty', function() {
+
+      // given
+      var viewer = new Viewer({ container: container });
+
+      function clearDiagram() {
+        viewer.clear();
+      }
+
+      // then
+      expect(clearDiagram).to.not.throw();
+    });
+
+
+    it('should remove di property', function(done) {
+
+      var xml = require('../fixtures/bpmn/simple.bpmn');
+
+      var viewer = new Viewer({ container: container }),
+          elementRegistry = viewer.get('elementRegistry');
+
+      viewer.importXML(xml, function(err, warnings) {
+
+        var elements = elementRegistry.getAll();
+
+        // when
+        viewer.clear();
+
+        // then
+        expect(elements.some(function(el) {
+          return el && el.businessObject && el.businessObject.di;
+        }), 'at least one element still has di').to.be.false;
+
+        done(err, warnings);
+      });
+    });
+
+  });
+
+
   it('default export', function() {
     expect(ViewerDefaultExport).to.equal(Viewer);
   });