事件处理程序。 当 CSS 动画到达其活动期的结束时发送此事件


var animEndHandler = target.onanimationend;

target.onanimationend = 事件处理函数

target(HTML 元素, document 或者 window) 的 CSS 动画已经开始,animationend (en-US)事件会触发同时事件处理函数会被调用。事件处理函数会接收到唯一的参数:AnimationEvent 描述发生的事件。


CSS content

Leaving out some bits of the CSS that don't matter for the discussion here, let's take a look at the styles for the box that we're animating. First is the box itself. We set its size, position, color, and layout. Note that there's nothing there about animation. That's because we don't want the box to start animating right away. We'll add the animation style later to start animating the box.

#box {
  width: var(--boxwidth);
  height: var(--boxwidth);
  left: 0;
  top: 0;
  border: 1px solid #7788FF;
  margin: 0;
  position: relative;
  background-color: #2233FF;
  display: flex;
  justify-content: center;

The animation sequence is described next. First, the "slideAnimation" class, which establishes the animation that will cause the box to move over the course of five seconds, one time, using the "slideBox" keyframe set. The keyframes are defined next; they describe an animation which causes the box to migrate from the top-left corner of the container to the bottom-right corner.

.slideAnimation {
  animation: 5s ease-in-out 0s 1 slideBox;

@keyframes slideBox {
  from {
  to {
    left:calc(100% - var(--boxwidth));
    top:calc(100% - var(--boxwidth))

Since the CSS describes the animation but doesn't connect it to the box, we'll need some JavaScript code to do that. We'll get to that shortly.

JavaScript content

Before we get to the animation code, we define a function which logs information to a box on the user's screen. We'll use this to show information about the events we receive. Note the use of AnimationEvent.animationName and AnimationEvent.elapsedTime to get information about the event which occurred.

function log(msg, event) {
  let logBox = document.getElementById("log");

  logBox.innerHTML += msg;

  if (event) {
    logBox.innerHTML += " <code>"+ event.animationName +
        "</code> at time " + event.elapsedTime.toFixed(2) +
        " seconds.";

  logBox.innerHTML += "\n";

Then we set up the event handlers for the animationstart and animationend events:

let box = document.getElementById("box");

box.onanimationstart = function(event) {
  log("Animation started", event);

box.onanimationend = function(event) {
  log("Animation stopped", event);

Finally, we set up a handler for a click on the button that runs the animation:

document.getElementById("play").addEventListener("click", function(event) {
  document.getElementById("box").className = "slideAnimation"; = "none";
}, false);

This sets the class of the box we want to animate to the class that contains the animation description, then hides the play button because this example will only run the animation once. For information about why, and how to support running an animation more than once, see Run an animation again in CSS Animations tips and tricks.


Assembled together, you get this:


Specification Status Comment
CSS Animations Level 1
Working Draft  


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