ViewTransition: ready property

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

The ready read-only property of the ViewTransition interface is a Promise that fulfills once the pseudo-element tree is created and the transition animation is about to start.

ready will reject if the transition cannot begin. This can be due to misconfiguration, for example, duplicate view-transition-names, or if the callback passed to Document.startViewTransition() throws or returns a promise that rejects.

Value

A Promise.

Examples

In the following example, ready is used to trigger a custom circular reveal view transition emanating from the position of the user's cursor on click, with animation provided by the Web Animations API.

js
// Store the last click event
let lastClick;
addEventListener("click", (event) => (lastClick = event));

function spaNavigate(data) {
  // Fallback for browsers that don't support this API:
  if (!document.startViewTransition) {
    updateTheDOMSomehow(data);
    return;
  }

  // Get the click position, or fallback to the middle of the screen
  const x = lastClick?.clientX ?? innerWidth / 2;
  const y = lastClick?.clientY ?? innerHeight / 2;
  // Get the distance to the furthest corner
  const endRadius = Math.hypot(
    Math.max(x, innerWidth - x),
    Math.max(y, innerHeight - y),
  );

  // Create a transition:
  const transition = document.startViewTransition(() => {
    updateTheDOMSomehow(data);
  });

  // Wait for the pseudo-elements to be created:
  transition.ready.then(() => {
    // Animate the root's new view
    document.documentElement.animate(
      {
        clipPath: [
          `circle(0 at ${x}px ${y}px)`,
          `circle(${endRadius}px at ${x}px ${y}px)`,
        ],
      },
      {
        duration: 500,
        easing: "ease-in",
        // Specify which pseudo-element to animate
        pseudoElement: "::view-transition-new(root)",
      },
    );
  });
}

This animation also requires the following CSS, to turn off the default CSS animation and stop the old and new view states from blending in any way (the new state "wipes" right over the top of the old state, rather than transitioning in):

css
::view-transition-image-pair(root) {
  isolation: auto;
}

::view-transition-old(root),
::view-transition-new(root) {
  animation: none;
  mix-blend-mode: normal;
  display: block;
}

Specifications

Specification
CSS View Transitions Module Level 1
# dom-viewtransition-ready

Browser compatibility

BCD tables only load in the browser

See also