June 27th, 2022 × #webapi#animations#transitions

Browser CSS Page Transitions API aka Shared Element Transitions

Discussion of a new browser API proposal for smooth page transitions on the web, allowing for animated transitions between pages similar to native mobile apps.


In this Hasty Treat, Scott and Wes talk about the new Browser CSS Page Transitions API proposal and what features it opens up for developers on the web.

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Show Notes

async function doTransition() {
  let transition = document.createDocumentTransition();
  // Specify offered elements. The tag below is used to refer
  // to the generated pseudo elemends in script/CSS.
  document.querySelector(".old-message").style.pageTransitionTag = "message";
  // The start() call triggers an async operation to capture
  // snapshots for the offered elements,
  await transition.start(async () => {
    // This callback is invoked by the browser when the capture
    // finishes and the DOM can be switched to the new state.
    // No frames are rendered until this callback returns.
    // Asynchronously load the new page.
    await coolFramework.changeTheDOMToPageB();
    // Clear the old message if that element is still in the page
    document.querySelector(".old-message").style.pageTransitionTag = "";
    // Set new message as the shared element 'message'
    document.querySelector(".new-message").style.pageTransitionTag = "message";
    // Set up animations using WA-API on the next frame.
    requestAnimationFrame(() => {
      document.documentElement.animate(keyframes, {
      pseudoElement: "::page-transition-container(message)",
    // Note that when this callback finishes, the animations will start with the tagged elements.

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