mouseenter与mouseover的区别

mouseenter | onmouseenter event

The event fires only if the mouse pointer is outside the boundaries of the object and the user moves the mouse pointer inside the boundaries of the object. If the mouse pointer is currently inside the boundaries of the object, for the event to fire, the user must move the mouse pointer outside the boundaries of the object and then back inside the boundaries of the object.

只有当鼠标指针在对象的边界之外，用户把鼠标移动到对象的边界内时，事件mouseenter才触发。如果鼠标当时正在边界内，用户想要触发该事件，需要把鼠标移动到对象边界外再移动到边界内。

因此，mouseenter不支持事件冒泡，所以导致在一个元素的子元素上进入或离开的时候会触发其mouseover和mouseout事件，但是却不会触发mouseenter和mouseleave事件。