Document: transitionrun event - Web APIs
bubbles yes cancelable no interface transitionevent event handler property ontransitionrun the original target for this event is the element that had the transition applied.
... examples this code adds a listener to the transitionrun event: document.addeventlistener('transitionrun', () => { console.log('transition is running but hasn't necessarily started transitioning yet'); }); the same, but using the ontransitionrun property instead of addeventlistener(): document.ontransitionrun = () => { console.log('transition started running'); }; see a live example of this event.

Document - Web APIs
globaleventhandlers.ontransitionrun an eventhandler called when a transitionrun event is sent, indicating that a css transition is running, though not nessarilty started.
... also available via the ontransitionrun property.

Window: transitionrun event - Web APIs
bubbles yes cancelable no interface transitionevent event handler property ontransitionrun the original target for this event is the element that had the transition applied.
... examples this code adds a listener to the transitionrun event: window.addeventlistener('transitionrun', () => { console.log('transition is running but hasn't necessarily started transitioning yet'); }); the same, but using the ontransitionrun property instead of addeventlistener(): window.ontransitionrun = () => { console.log('transition started running'); }; see a live example of this event.

Document: transitionstart event - Web APIs
examples this code adds a listener to the transitionstart event: document.addeventlistener('transitionstart', () => { console.log('started transitioning'); }); the same, but using the ontransitionstart property instead of addeventlistener(): document.ontransitionrun = () => { console.log('started transitioning'); }; see a live example of this event.

GlobalEventHandlers.ontransitioncancel - Web APIs
let box = document.queryselector(".box"); box.ontransitionrun = function(event) { box.innerhtml = "zooming..."; } box.ontransitionend = function(event) { box.innerhtml = "done!"; } box.onclick = function() { box.style.display = 'none'; timeout = window.settimeout(appear, 2000); function appear() { box.style.display = 'block'; } } box.ontransitioncancel = function(event) { console.log('transitioncancel fired after ' + event.elapsedtime + ...

GlobalEventHandlers.ontransitionend - Web APIs
let box = document.queryselector(".box"); box.ontransitionrun = function(event) { box.innerhtml = "zooming..."; } box.ontransitionend = function(event) { box.innerhtml = "done!"; } result the resulting content looks like this: notice what happens when you hover your mouse cursor over the box, then move it away.

GlobalEventHandlers - Web APIs
globaleventhandlers.ontransitionrun an eventhandler called when a transitionrun event is sent, indicating that a css transition is running, though not nessarilty started.

HTMLElement: transitionrun event - Web APIs
bubbles yes cancelable no interface transitionevent event handler property ontransitionrun examples this code adds a listener to the transitionrun event: el.addeventlistener('transitionrun', () => { console.log('transition is running but hasn\'t necessarily started transitioning yet'); }); the same, but using the ontransitionrun property instead of addeventlistener(): el.ontransitionrun = () => { console.log('transition started running, and will start transitioning when the transition delay has expired'); }; live example in the following example, we have a simple <div> element, styled with a transition that inclu...

HTMLElement: transitionstart event - Web APIs
bubbles yes cancelable no interface transitionevent event handler property ontransitionstart examples this code adds a listener to the transitionstart event: element.addeventlistener('transitionstart', () => { console.log('started transitioning'); }); the same, but using the ontransitionstart property instead of addeventlistener(): element.ontransitionrun = () => { console.log('started transitioning'); }; live example in the following example, we have a simple <div> element, styled with a transition that includes a delay: <div class="transition">hover over me</div> <div class="message"></div> .transition { width: 100px; height: 100px; background: rgba(255,0,0,1); transition-property: transform, background; transition-duration: 2s; ...

HTMLElement - Web APIs
also available via the ontransitionrun property.

Window: transitionstart event - Web APIs
examples this code adds a listener to the transitionstart event: window.addeventlistener('transitionstart', () => { console.log('started transitioning'); }); the same, but using the ontransitionstart property instead of addeventlistener(): window.ontransitionrun = () => { console.log('started transitioning'); }; see a live example of this event.

Window - Web APIs
also available via the ontransitionrun property.