The updateCallbackDone read-only property of the ViewTransition interface is a Promise that fulfills when the promise returned by the document.startViewTransition() method's callback fulfills, or rejects when it rejects.
updateCallbackDone is useful when you don't care about the success/failure of a same-document (SPA) view transition animation, and just want to know if and when the DOM is updated.
Note: In the case of a cross-document (MPA) view transition, the updateCallbackDone promise of the associated ViewTransition is automatically fulfilled.
A Promise.
// start new SPA view transition
const transition = document.startViewTransition(() => displayNewImage());
transition.updateCallbackDone.then(() => {
// Respond to the DOM being updated successfully
});See Transitions as an enhancement for a useful example.