Document: prerenderingchange event

The prerenderingchange event is fired on a prerendered document when it is activated (i.e., the user views the page).

Syntax

Use the event name in methods like addEventListener(), or set an event handler property.

addEventListener("prerenderingchange", (event) => { })

onprerenderingchange = (event) => { }

Event type

A generic Event.

Examples

Preventing code from running during prerendering

The example shows how to defer code, that would otherwise run during prerendering, until after page activation. This is useful for deferring analytics code, which is only relevant when and if the page is actually viewed.

The code checks if prerendering is running using Document.prerendering, and if so adds an event listener to run an analytics initialization function once the page is activated. On a page that is not prerendering the analytics code is run immediately.

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

Note that this kind of code should not be used for measuring how often a prerender is activated, because the code may run after a prerendered page has already activated.

Measuring prerendering activations

This code shows how to measure how often a prerender is activated. It uses the prerenderingchange to track activation events, and Performance.getEntriesByType() to track navigation activations.

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

Browser compatibility

See also

• Speculation Rules API
• prerendering property
• PerformanceNavigationTiming.activationStart property