The finished read-only property of the ViewTransition interface is a Promise that fulfills once the transition animation is finished, and the new page view is visible and interactive to the user.
finished only rejects if the callback passed to document.startViewTransition()throws or returns a promise that rejects, which indicates that the new state of the page wasn't created.
If a transition animation fails to start, or is skipped during the animation using ViewTransition.skipTransition(), the end state is still reached therefore finished still fulfills.
Sometimes certain navigations will require specifically tailored transitions, for example a 'back' navigation may want a different transition to a 'forward' navigation. The best way to handle such cases is to set a class name on the <html> element, handle the transition — applying the correct animation using a tailored selector — and then remove the class name once the transition is finished.
async function handleTransition() {
if (isBackNavigation) {
document.documentElement.classList.add("back-transition");
}
const transition = document.startViewTransition(() =>
updateTheDOMSomehow(data),
);
try {
await transition.finished;
} finally {
document.documentElement.classList.remove("back-transition");
}
}
Note: isBackNavigation isn't a built-in feature; it's a theoretical function that could perhaps be implemented using the Navigation API or similar.