Called when user moves over an item or item's icon, handle, badge or count You can add event listener during the object creation: let sidebar = new w2sidebar({ name : 'sidebar', nodes: [ { id: 'id-1', text: 'Level 1' }, { id: 'id-2', text: 'Level 2' }, { id: 'id-3', text: 'Level 3' } ], onMouseEnter(event) { console.log(event) } }) or after the object has been created: w2ui.sidebar.on('onMouseEnter', function(event) { console.log(event) }) This event is triggered to show the tooltip over the hangle, icon, badge or count or just catch event when user moves mouse over the item. You can find out what part of the item is move on if you read `event.detail`, which you can canel and no tooltip (if it is define) will be show. The event handler is called before the default action of the event is triggered. You can cancel the default action by calling event.preventDefault(). To perform an action after the event is fully processed, define event.onComplete function. See events page in utilities for more details.