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---
title: ServiceWorker.onstatechange
slug: Web/API/ServiceWorker/statechange_event
---
{{APIRef("Service Workers API")}}
Обработчик события, вызываемый при срабатывании события `statechange`; по сути, срабатывает при изменении {{domxref("ServiceWorker.state")}}.
## Синтаксис
```
ServiceWorker.onstatechange = function(statechangeevent) { ... }
ServiceWorker.addEventListener('statechange', function(statechangeevent) { ... } )
```
## Примеры
Данный фрагмент кода из [примера событий service worker](https://github.com/GoogleChrome/samples/blob/gh-pages/service-worker/registration-events/index.html) ([демо](https://googlechrome.github.io/samples/service-worker/registration-events/)) возвращает состояние при каждом его изменении.
```js
var 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", function (e) {
logState(e.target.state);
});
}
```
Обратите внимание, что при срабатывании `statechange`, ссылки на service worker могли измениться. Например:
```js
navigator.serviceWorker.register(..).then(function(swr) {
swr.installing.state == "installing"
swr.installing.onstatechange = function() {
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.
}
})
```
## Спецификации
{{Specifications}}
## Совместимость с браузерами
{{Compat}}