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测验题

What is the difference between `mouseenter` and `mouseover` event in JavaScript and browsers?

Topics
JAVASCRIPTHTML
在GitHub上编辑

TL;DR

The main difference lies in the bubbling behavior of mouseenter and mouseover events. mouseenter does not bubble while mouseover bubbles.

mouseenter events do not bubble. The mouseenter event is triggered only when the mouse pointer enters the element itself, not its descendants. If a parent element has child elements, and the mouse pointer enters child elements, the mouseenter event will not be triggered on the parent element again, it's only triggered once upon entry of parent element without regard for its contents. If both parent and child have mouseenter listeners attached and the mouse pointer moves from the parent element to the child element, mouseenter will only fire for the child.

mouseover events bubble up the DOM tree. The mouseover event is triggered when the mouse pointer enters the element or one of its descendants. If have a parent element has child elements, and the mouse pointer enters child elements, the mouseover event will be triggered on the parent element again as well. If the parent element has multiple child elements, this can result in multiple event callbacks fired. If there are child elements, and the mouse pointer moves from the parent element to the child element, mouseover will fire for both the parent and the child.

Propertymouseentermouseover
BubblingNoYes
TriggerOnly when entering itselfWhen entering itself and when entering descendants

mouseenter event:

  • Does not bubble: The mouseenter event does not bubble. It is only triggered when the mouse pointer enters the element to which the event listener is attached, not when it enters any child elements.
  • Triggered once: The mouseenter event is triggered only once when the mouse pointer enters the element, making it more predictable and easier to manage in certain scenarios.

A use case for mouseenter is when you want to detect the mouse entering an element without worrying about child elements triggering the event multiple times.

mouseover Event:

  • Bubbles up the DOM: The mouseover event bubbles up through the DOM. This means that if you have an event listener on a parent element, it will also trigger when the mouse pointer moves over any child elements.
  • Triggered multiple times: The mouseover event is triggered every time the mouse pointer moves over an element or any of its child elements. This can lead to multiple triggers if you have nested elements.

A use case for mouseover is when you want to detect when the mouse enters an element or any of its children and are okay with the events triggering multiple times.

Example

Here's an example demonstrating the difference between mouseover and mouseenter events:

<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Mouse Events Example</title>
    <style>
      .parent {
        width: 200px;
        height: 200px;
        background-color: lightblue;
        padding: 20px;
      }
      .child {
        width: 100px;
        height: 100px;
        background-color: lightcoral;
      }
    </style>
  </head>
  <body>
    <div class="parent">
      Parent Element
      <div class="child">Child Element</div>
    </div>


    <script>
      const parent = document.querySelector('.parent');
      const child = document.querySelector('.child');


      // Mouseover event on parent.
      parent.addEventListener('mouseover', () => {
        console.log('Mouseover on parent');
      });


      // Mouseenter event on parent.
      parent.addEventListener('mouseenter', () => {
        console.log('Mouseenter on parent');
      });


      // Mouseover event on child.
      child.addEventListener('mouseover', () => {
        console.log('Mouseover on child');
      });


      // Mouseenter event on child.
      child.addEventListener('mouseenter', () => {
        console.log('Mouseenter on child');
      });
    </script>
  </body>
</html>

Expected behavior

  • When the mouse enters the parent element:
    • The mouseover event on the parent will trigger.
    • The mouseenter event on the parent will trigger.
  • When the mouse enters the child element:
    • The mouseover event on the parent will trigger again because mouseover bubbles up from the child.
    • The mouseover event on the child will trigger.
    • The mouseenter event on the child will trigger.
    • The mouseenter event on the parent will not trigger again because mouseenter does not bubble.

Further reading

在GitHub上编辑
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