ServiceWorker: statechange event

Secure contextAvailable in workers

The statechange event fires anytime the state changes.

Syntax

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

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 state and returns its value.

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:

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

Browser compatibility