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