Fixed hover events for HTML elements (#2539)

lib/timeline/component/ItemSet.js

@@ -1875,6 +1875,13 @@ ItemSet.prototype._onMouseOver = function (event) {
   var item = this.itemFromTarget(event);
   if (!item) return;
 
+  // Item we just left
+  var related = this.itemFromRelatedTarget(event);
+  if (item === related) {
+    // We haven't changed item, just element in the item
+    return;
+  }
+
   if (item.getTitle()) {
     if (item.popup == null) {
       item.setPopup(new Popup(this.body.dom.root));
@@ -1897,6 +1904,13 @@ ItemSet.prototype._onMouseOut = function (event) {
   var item = this.itemFromTarget(event);
   if (!item) return;
 
+  // Item we are going to
+  var related = this.itemFromRelatedTarget(event);
+  if (item === related) {
+    // We aren't changing item, just element in the item
+    return;
+  }
+
   if (item.popup != null) {
     item.popup.hide();
   }
@@ -2118,22 +2132,42 @@ ItemSet._getItemRange = function(itemsData) {
   }
 };
 
+/**
+ * Find an item from an element:
+ * searches for the attribute 'timeline-item' in the element's tree
+ * @param {HTMLElement} element
+ * @return {Item | null} item
+ */
+ItemSet.prototype.itemFromElement = function(element) {
+  var cur = element;
+  while (cur) {
+    if (cur.hasOwnProperty('timeline-item')) {
+      return cur['timeline-item'];
+    }
+    cur = cur.parentNode;
+  }
+
+  return null;
+};
+
 /**
  * Find an item from an event target:
  * searches for the attribute 'timeline-item' in the event target's element tree
  * @param {Event} event
  * @return {Item | null} item
  */
 ItemSet.prototype.itemFromTarget = function(event) {
-  var target = event.target;
-  while (target) {
-    if (target.hasOwnProperty('timeline-item')) {
-      return target['timeline-item'];
-    }
-    target = target.parentNode;
-  }
+  return this.itemFromElement(event.target);
+};
 
-  return null;
+/**
+ * Find an item from an event's related target:
+ * searches for the attribute 'timeline-item' in the related target's element tree
+ * @param {Event} event
+ * @return {Item | null} item
+ */
+ItemSet.prototype.itemFromRelatedTarget = function(event) {
+  return this.itemFromElement(event.relatedTarget);
 };
 
 /**