Document: prerendering property

Limited availability

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

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The prerendering read-only property of the Document interface returns true if the document is currently in the process of prerendering, as initiated via the Speculation Rules API.

Value

A boolean. Returns true if the document is currently in the process of prerendering, and false if it is not. false will be returned for documents that have finished prerendering, and documents that were not prerendered.

Examples

To run an activity while the page is prerendering, you can check for the prerendering property. You could for example run some analytics:

js
if (document.prerendering) {
  analytics.sendInfo("got this far during prerendering!");
}

When a prerendered document is activated, PerformanceNavigationTiming.activationStart is set to a DOMHighResTimeStamp value representing the time between when the prerender was started and the document was actually activated. The following function can check for prerendering and prerendered pages:

js
function pagePrerendered() {
  return (
    document.prerendering ||
    performance.getEntriesByType("navigation")[0]?.activationStart > 0
  );
}

When the prerendered page is activated by the user viewing the page, the prerenderingchange event will fire. This can be used to enable activities that previously would be started by default on page load but which you wish to delay until the page is actually viewed by the user. The following code sets up an event listener to run a function once prerendering has finished, on a prerendered page, or runs it immediately on a non-prerendered page:

js
if (document.prerendering) {
  document.addEventListener("prerenderingchange", initAnalytics, {
    once: true,
  });
} else {
  initAnalytics();
}

Note: See the Speculation Rules API landing page and particularly the Unsafe speculative loading conditions section for more information on the kinds of activities you might wish to delay.

To measure how often a prerender is activated, combine all three APIs: document.prerendering to detect cases where the page is currently prerendering, prerenderingchange to watch for activations in that case, and activationStart to check for cases where the page was prerendered in the past.

js
if (document.prerendering) {
  document.addEventListener(
    "prerenderingchange",
    () => {
      console.log("Prerender activated after this script ran");
    },
    { once: true },
  );
} else if (performance.getEntriesByType("navigation")[0]?.activationStart > 0) {
  console.log("Prerender activated before this script ran");
} else {
  console.log("This page load was not via prerendering");
}

Specifications

Specification
Prerendering Revamped
# dom-document-prerendering

Browser compatibility

Report problems with this compatibility data on GitHub
desktopmobile
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
prerendering
Experimental

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support
No support
No support
Experimental. Expect behavior to change in the future.

See also