The updateCallbackDone read-only property of the ViewTransition interface is a Promise that fulfills when the promise returned by the document.startViewTransition()'s callback fulfills, or rejects when it rejects.

updateCallbackDone is useful when you don't care about the success/failure of the transition animation, and just want to know if and when the DOM is updated.

A promise.

// start new 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.

• Smooth and simple transitions with the View Transitions API