ServiceWorker: statechange event
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
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