ServiceWorker: statechange event

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since April 2018.

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Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

Note: This feature is available in Web Workers.

The statechange event fires anytime the ServiceWorker.state changes.

Syntax

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

js
addEventListener("statechange", (event) => {});

onstatechange = (event) => {};

Event type

A generic Event.

Examples

This code snippet is from the service worker registration-events sample (live demo). The code listens for any change in the ServiceWorker.state and returns its value.

js
let serviceWorker;
if (registration.installing) {
  serviceWorker = registration.installing;
  document.querySelector("#kind").textContent = "installing";
} else if (registration.waiting) {
  serviceWorker = registration.waiting;
  document.querySelector("#kind").textContent = "waiting";
} else if (registration.active) {
  serviceWorker = registration.active;
  document.querySelector("#kind").textContent = "active";
}

if (serviceWorker) {
  logState(serviceWorker.state);
  serviceWorker.addEventListener("statechange", (e) => {
    logState(e.target.state);
  });
}

Note that when statechange fires, the service worker's references may have changed. For example:

js
navigator.serviceWorker.register("/sw.js").then((swr) => {
  swr.installing.state = "installing";
  swr.installing.onstatechange = () => {
    swr.installing = null;
    // At this point, swr.waiting OR swr.active might be true. This is because the statechange
    // event gets queued, meanwhile the underlying worker may have gone into the waiting
    // state and will be immediately activated if possible.
  };
});

Specifications

Specification
Service Workers
# dom-serviceworker-onstatechange

Browser compatibility