An event handler for the transitionend event. This event is sent to when a CSS transition completes.

If the transition is removed from its target node before the transition completes execution, the transitionend event won't be generated. One way this can happen is by changing the value of the transition-property attribute which applies to the target. Another is if the display attribute is set to "none".


var transitionEndHandler = target.ontransitionend;

target.ontransitionend = Function


A Function to be called when a transitionend event occurs indicating that a CSS transition has completed on the target, where the target object is an HTML element (HTMLElement), document (Document), or window (Window). The function receives as input a single parameter: a TransitionEvent object describing the event which occurred; the event's TransitionEvent.elapsedTime property's value should be the same as the value of transition-duration.

elapsedTime does not include time prior to the transition effect beginning; that means that the value of transition-delay doesn't affect the value of elapsedTime, which is zero until the delay period ends and the animation begins.


In this example, we use the transitionrun and transitionend events to detect when the transition begins and ends, to cause a text update to occur during the transition. This could also be used to trigger animations or other effects, to allow chaining of reactions.

HTML content

This simply creates a <div> which we'll style with CSS below to make into a box that resizes and changes color and such.

<div class="box"></div>

CSS content

The CSS below styles the box and applies a transition effect which makes the box's color and size change, and causes the box to rotate, while the mouse cursor hovers over it.

.box {
  margin-left: 70px;
  margin-top: 30px;
  border-style: solid;
  border-width: 1px;
  display: block;
  width: 100px;
  height: 100px;
  background-color: #0000FF;
  color: #FFFFFF;
  padding: 20px;
  font: bold 1.6em "Helvetica", "Arial", sans-serif;
  -webkit-transition: width 2s, height 2s, background-color 2s, -webkit-transform 2s, color 2s;
  transition: width 2s, height 2s, background-color 2s, transform 2s, color 2s;

.box:hover {
  background-color: #FFCCCC;
  color: #000000;
  width: 200px;
  height: 200px;
  -webkit-transform: rotate(180deg);
  transform: rotate(180deg);

JavaScript content

Next, we need to establish our event handlers to change the text content of the box when the transition begins and ends.

let box = document.querySelector(".box");
box.ontransitionrun = function(event) {
  box.innerHTML = "Zooming...";
box.ontransitionend = function(event) {
  box.innerHTML = "Done!";


The resulting content looks like this:

Notice what happens when you hover your mouse cursor over the box, then move it away.


Browser compatibilityUpdate compatibility data on GitHub

Chrome Edge Firefox Internet Explorer Opera Safari
Basic support Yes
Uses the non-standard name: onwebkittransitionend
? 51 ? ? Yes
Android webview Chrome for Android Edge Mobile Firefox for Android Opera for Android iOS Safari Samsung Internet
Basic support Yes
Uses the non-standard name: onwebkittransitionend
Uses the non-standard name: onwebkittransitionend
? 51 ? Yes ?

See also

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