js简单自定义事件与主动触发事件

 var events = {
     addHandler: function (element, eventType, handler) {
         if (element.addEventListener) {
             return element.addEventListener(eventType, handler, false);
         } else {
             return element.attachEvent("on" + eventType, handler);
         }
     },
     removeHandler: function (element, eventType, handler) {
         if (element.removeEventListener) {
             return element.removeEventListener(eventType, handler, false);
         } else {
             return element.detachEvent("on" + eventType, handler);
         }
     },
     getEvent: function (event) {
         return event || window.event;
     },
 }

//执行鼠标进入事件
document.querySelector('#test').dispatchEvent(new Event('mouseenter'))