ServiceWorker.onstatechange

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.

实验性: 这是一项实验性技术
在将其用于生产之前，请仔细检查浏览器兼容性表格。

一个 EventListener 联动的属性，其会被任何 stagechange 类型事件抛出时联动; 它也基本上能在任何时候ServiceWorker.state 改变时被抛出。

语法

ServiceWorker.onstatechange = function(statechangeevent) { ... }
ServiceWorker.addEventListener('statechange', function(statechangeevent) { ... } )

示例

这段代码出自 service worker registration-events sample (live demo). 它会监听 ServiceWorker.state 的改变并返回它的值。

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);
  });
}

注意当statechange 抛出时，service worker 的引用可能已经改变。例如：

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.
  }
})

规范

Specification
Service Workers
# dom-serviceworker-onstatechange

浏览器兼容性