javascript - 成功安装 Service Worker 时更新 UI

Question

看起来 Service Worker 在工作人员上下文中运行并且无权访问 DOM。但是，一旦安装了 Service Worker，我希望我的用户知道该应用程序现在可以离线工作。我怎样才能做到这一点？

Answer 1

当 Service Worker 处于 时activated state，这是显示 toast ' Content is cached for offline use' 的最佳时机。在注册服务人员时尝试以下代码。

if ('serviceWorker' in navigator) {
  navigator.serviceWorker.register('/service-worker.js').then(function(reg) {
    // updatefound is fired if service-worker.js changes.
    reg.onupdatefound = function() {
      var installingWorker = reg.installing;

      installingWorker.onstatechange = function() {
        switch (installingWorker.state) {
          case 'installed':
            if (navigator.serviceWorker.controller) {
              // At this point, the old content will have been purged and the fresh content will
              // have been added to the cache.
              // It's the perfect time to display a "New content is available; please refresh."
              // message in the page's interface.
              console.log('New or updated content is available.');
            } else {
              // At this point, everything has been precached.
              // It's the perfect time to display a "Content is cached for offline use." message.
              console.log('Content is now available offline!');
            }
            break;

          case 'redundant':
            console.error('The installing service worker became redundant.');
            break;
        }
      };
    };
  }).catch(function(e) {
    console.error('Error during service worker registration:', e);
  });
}

Answer 2

在上面测试了@Prototype Chain的答案之后，我想使用named functions而不是嵌套anonymous functions作为事件处理程序，以使代码更符合我的口味，并希望以后/其他人更容易理解。

但只有在花了一些时间对文档进行排序之后，我才设法在正确的对象上监听正确的事件。因此，在这里分享我的工作示例，希望可以将其他人从繁琐的过程中拯救出来。

    // make sure that Service Workers are supported.
    if (navigator.serviceWorker) {
        navigator.serviceWorker.register('/sw.js')
            .then(function (registration) {
                console.log("ServiceWorker registered");

                // updatefound event is fired if sw.js changed
                registration.onupdatefound = swUpdated;
            }).catch(function (e) {
            console.log("Failed to register ServiceWorker", e);
        })
    }

    function swUpdated(e) {
        console.log('swUpdated');
        // get the SW which being installed
        var sw = e.target.installing;
        // listen for installation stage changes
        sw.onstatechange = swInstallationStateChanged;
    }

    function swInstallationStateChanged(e) {
        // get the SW which being installed
        var sw = e.target;
        console.log('swInstallationStateChanged: ' + sw.state);

        if (sw.state == 'installed') {
            // is any sw already installed? This function will run 'before' 'SW's activate' handler, so we are checking for any previous sw, not this one.
            if (navigator.serviceWorker.controller) {
                console.log('Content has updated!');
            } else {
                console.log('Content is now available offline!');
            }
        }

        if (sw.state == 'activated') {
            // new|updated SW is now activated.
            console.log('SW is activated!');
        }
    }