mouseenter

当定点设备（通常指鼠标）移动到元素上时就会触发 mouseenter 事件

类似 mouseover，它们两者之间的差别是 mouseenter 不会冒泡（bubble），也就是说当指针从它的子层物理空间移到它的物理空间上时不会触发

One mouseenter event is sent to each element of the hierarchy when entering them. Here 4 events are sent to the four elements of the hierarchy when the pointer reaches the text.

One single mouseover event is sent to the deepest element of the DOM tree, then it bubbles up the hierarchy until it is canceled by a handler or reaches the root.

With deep hierarchies, the amount of mouseenter events sent can be quite huge and cause significant performance problems. In such cases, it is better to listen for mouseover events.

Combined with the behavior of its symmetrical event, mouseleave, the mouseenter DOM Event acts in a very similar way to the CSS :hover pseudo-class.

General info

Specification

DOM L3

Interface

MouseEvent

Synchronicity

Synchronous

Bubbles

No

Cancelable

No

Target

Element

Default Action

None

Properties

Examples

The mouseover documentation has an example illustrating the difference between mouseover and mouseenter.

The following example illustrates how to use mouseover to simulate the principle of event delegation for the mouseenter event.

<ul id="test">
  <li>
    <ul class="enter-sensitive">
      <li>item 1-1</li>
      <li>item 1-2</li>
    </ul>
  </li>
  <li>
    <ul class="enter-sensitive">
      <li>item 2-1</li>
      <li>item 2-2</li>
    </ul>
  </li>
</ul>
<script>
  var delegationSelector = ".enter-sensitive";
  document.getElementById("test").addEventListener("mouseover", function( event ) {
    var target = event.target,
        related = event.relatedTarget,
        match;
    // search for a parent node matching the delegation selector
    while ( target && target != document && !( match = matches( target, delegationSelector ) ) ) {
        target = target.parentNode;
    }
    // exit if no matching node has been found
    if ( !match ) { return; }
    // loop through the parent of the related target to make sure that it's not a child of the target
    while ( related && related != target && related != document ) {
        related = related.parentNode;
    }
    // exit if this is the case
    if ( related == target ) { return; }
    // the "delegated mouseenter" handler can now be executed
    // change the color of the text
    target.style.color = "orange";
    // reset the color after a small amount of time
    setTimeout(function() {
        target.style.color = "";
    }, 500);
  }, false);
  // function used to check if a DOM element matches a given selector
  // the following code can be replaced by this IE8 compatible function: https://gist.github.com/2851541
  function matches( elem, selector ){
    // the matchesSelector is prefixed in most (if not all) browsers
    return elem.matchesSelector( selector );
  };
</script>

Browser compatibility

[1] Implemented in bug 236215.

[2] Implemented in bug 432698.

[3] Safari 7 fires the event in many situations where it's not allowed to, making the whole event useless. See bug 470258 for the description of the bug (it existed in old Chrome versions as well). Safari 8 has correct behavior

[4] Implemented in bug 218093.

See also

• mousedown
• mouseup
• mousemove
• click
• dblclick
• mouseover
• mouseout
• mouseenter
• mouseleave
• contextmenu