fix(jqLite): correct implementation of mouseenter/mouseleave event

Implement mouseenter/mouseleave event referring to
http://www.quirksmode.org/js/events_mouse.html#link8 and jQuery source
code(not dependent on jQuery).
The old implementation is wrong. When moving mouse from a parent element
into a child element, it would trigger mouseleave event, which should not.
And the old test about mouseenter/mouseleave is wrong too. It just
triggers mouseover and mouseout events, cannot describe the process of mouse
moving from one element to another element, which is important for
mouseenter/mouseleave.

Closes #2131, #1811

src/jqLite.js

@@ -607,23 +607,43 @@ forEach({
 
       if (!eventFns) {
         if (type == 'mouseenter' || type == 'mouseleave') {
-          var counter = 0;
+          var contains = document.body.contains || document.body.compareDocumentPosition ?
+          function( a, b ) {
+            var adown = a.nodeType === 9 ? a.documentElement : a,
+            bup = b && b.parentNode;
+            return a === bup || !!( bup && bup.nodeType === 1 && (
+              adown.contains ?
+              adown.contains( bup ) :
+              a.compareDocumentPosition && a.compareDocumentPosition( bup ) & 16
+              ));
+            } :
+            function( a, b ) {
+              if ( b ) {
+                while ( (b = b.parentNode) ) {
+                  if ( b === a ) {
+                    return true;
+                  }
+                }
+              }
+              return false;
+            };	
 
-          events.mouseenter = [];
-          events.mouseleave = [];
+          events[type] = [];
+
+		  // Refer to jQuery's implementation of mouseenter & mouseleave
+          // Read about mouseenter and mouseleave:
+          // http://www.quirksmode.org/js/events_mouse.html#link8
+          var eventmap = { mouseleave : "mouseout", mouseenter : "mouseover"}          
+          bindFn(element, eventmap[type], function(event) {
+            var ret, target = this, related = event.relatedTarget;
+            // For mousenter/leave call the handler if related is outside the target.
+            // NB: No relatedTarget if the mouse left/entered the browser window
+            if ( !related || (related !== target && !contains(target, related)) ){
+              handle(event, type);
+            }	
 
-          bindFn(element, 'mouseover', function(event) {
-            counter++;
-            if (counter == 1) {
-              handle(event, 'mouseenter');
-            }
-          });
-          bindFn(element, 'mouseout', function(event) {
-            counter --;
-            if (counter == 0) {
-              handle(event, 'mouseleave');
-            }
           });
+
         } else {
           addEventListenerFn(element, type, handle);
           events[type] = [];

test/jqLiteSpec.js

@@ -775,13 +775,9 @@ describe('jqLite', function() {
 
         parent.bind('mouseenter', function() { log += 'parentEnter;'; });
         parent.bind('mouseleave', function() { log += 'parentLeave;'; });
-        parent.mouseover = function() { browserTrigger(parent, 'mouseover'); };
-        parent.mouseout = function() { browserTrigger(parent, 'mouseout'); };
 
         child.bind('mouseenter', function() { log += 'childEnter;'; });
         child.bind('mouseleave', function() { log += 'childLeave;'; });
-        child.mouseover = function() { browserTrigger(child, 'mouseover'); };
-        child.mouseout = function() { browserTrigger(child, 'mouseout'); };
       });
 
       afterEach(function() {
@@ -790,20 +786,49 @@ describe('jqLite', function() {
 
       it('should fire mouseenter when coming from outside the browser window', function() {
         if (window.jQuery) return;
-        parent.mouseover();
+        var browserMoveTrigger = function(from, to){
+          var fireEvent = function(type, element, relatedTarget){
+            var msie = parseInt((/msie (\d+)/.exec(navigator.userAgent.toLowerCase()) || [])[1]);
+            if (msie < 9){
+              var evnt = document.createEventObject();
+              evnt.srcElement = element;
+              evnt.relatedTarget = relatedTarget;		
+              element.fireEvent('on' + type, evnt);
+              return;
+            };
+            var evnt = document.createEvent('MouseEvents'),
+            originalPreventDefault = evnt.preventDefault,
+            appWindow = window,
+            fakeProcessDefault = true,
+            finalProcessDefault;
+
+            evnt.preventDefault = function() {
+              fakeProcessDefault = false;
+              return originalPreventDefault.apply(evnt, arguments);
+            };
+
+            var x = 0, y = 0;
+            evnt.initMouseEvent(type, true, true, window, 0, x, y, x, y, false, false,
+            false, false, 0, relatedTarget);
+
+            element.dispatchEvent(evnt);
+          };
+          fireEvent('mouseout', from[0], to[0]);
+          fireEvent('mouseover', to[0], from[0]);
+        };
+
+        browserMoveTrigger(root, parent);
         expect(log).toEqual('parentEnter;');
 
-        child.mouseover();
-        expect(log).toEqual('parentEnter;childEnter;');
-        child.mouseover();
+        browserMoveTrigger(parent, child);
         expect(log).toEqual('parentEnter;childEnter;');
 
-        child.mouseout();
-        expect(log).toEqual('parentEnter;childEnter;');
-        child.mouseout();
+        browserMoveTrigger(child, parent);
         expect(log).toEqual('parentEnter;childEnter;childLeave;');
-        parent.mouseout();
+
+        browserMoveTrigger(parent, root);
         expect(log).toEqual('parentEnter;childEnter;childLeave;parentLeave;');
+
       });
     });
   });