Question

我已经将service-worker.js和manifest添加到我的网站，并使用灯塔测试了该页面，显示我的网页已准备好向用户显示“添加到主屏幕”。但是如果用户在没有第一次解除提示的情况下关闭选项卡，则提示不显示两次。是否有其他方法可以实现此目的？这是我的清单

{
  "short_name": "TestApp",
  "name": "Long Name",
  "icons": [
    {
      "src":"images/favicon-192.png",
      "sizes": "192x192",
      "type": "image/png"
    },
    {
      "src":"images/favicon-256.png",
      "sizes": "256x256",
      "type": "image/png"
    },
    {
      "src":"images/favicon-384.png",
      "sizes": "384x384",
      "type": "image/png"
    },
    {
      "src":"images/favicon-512.png",
      "sizes": "512x512",
      "type": "image/png"
    }                
  ],
  "start_url": "/",
  "background_color": "#fff",
  "theme_color": "#d2d2d2",
  "display": "standalone"
}

这是我的服务工作者javascript文件

/*
 Copyright 2015 Google Inc. All Rights Reserved.
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at
 http://www.apache.org/licenses/LICENSE-2.0
 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
*/

'use strict';

// Incrementing CACHE_VERSION will kick off the install event and force previously cached
// resources to be cached again.
const CACHE_VERSION = 3;
let CURRENT_CACHES = {
  offline: 'offline-v' + CACHE_VERSION
};
const OFFLINE_URL = 'offline.html';

function createCacheBustedRequest(url) {
  let request = new Request(url, {cache: 'reload'});
  // See https://fetch.spec.whatwg.org/#concept-request-mode
  // This is not yet supported in Chrome as of M48, so we need to explicitly check to see
  // if the cache: 'reload' option had any effect.
  if ('cache' in request) {
    return request;
  }

  // If {cache: 'reload'} didn't have any effect, append a cache-busting URL parameter instead.
  let bustedUrl = new URL(url, self.location.href);
  bustedUrl.search += (bustedUrl.search ? '&' : '') + 'cachebust=' + Date.now();
  return new Request(bustedUrl);
}


self.addEventListener('install', event => {
  event.waitUntil(
    // We can't use cache.add() here, since we want OFFLINE_URL to be the cache key, but
    // the actual URL we end up requesting might include a cache-busting parameter.
    fetch(createCacheBustedRequest(OFFLINE_URL)).then(function(response) {
      return caches.open(CURRENT_CACHES.offline).then(function(cache) {
        return cache.put(OFFLINE_URL, response);
      });
    })
  );
});

self.addEventListener('activate', event => {
  // Delete all caches that aren't named in CURRENT_CACHES.
  // While there is only one cache in this example, the same logic will handle the case where
  // there are multiple versioned caches.
  let expectedCacheNames = Object.keys(CURRENT_CACHES).map(function(key) {
    return CURRENT_CACHES[key];
  });

  event.waitUntil(
    caches.keys().then(cacheNames => {
      return Promise.all(
        cacheNames.map(cacheName => {
          if (expectedCacheNames.indexOf(cacheName) === -1) {
            // If this cache name isn't present in the array of "expected" cache names,
            // then delete it.
            console.log('Deleting out of date cache:', cacheName);
            return caches.delete(cacheName);
          }
        })
      );
    })
  );
});

self.addEventListener('fetch', event => {
  // We only want to call event.respondWith() if this is a navigation request
  // for an HTML page.
  // request.mode of 'navigate' is unfortunately not supported in Chrome
  // versions older than 49, so we need to include a less precise fallback,
  // which checks for a GET request with an Accept: text/html header.
  if (event.request.mode === 'navigate' ||
      (event.request.method === 'GET' &&
       event.request.headers.get('accept').includes('text/html'))) {
    console.log('Handling fetch event for', event.request.url);
    event.respondWith(
      fetch(event.request).catch(error => {
        // The catch is only triggered if fetch() throws an exception, which will most likely
        // happen due to the server being unreachable.
        // If fetch() returns a valid HTTP response with an response code in the 4xx or 5xx
        // range, the catch() will NOT be called. If you need custom handling for 4xx or 5xx
        // errors, see https://github.com/GoogleChrome/samples/tree/gh-pages/service-worker/fallback-response
        console.log('Fetch failed; returning offline page instead.', error);
        return caches.match(OFFLINE_URL);
      })
    );
  }

  // If our if() condition is false, then this fetch handler won't intercept the request.
  // If there are any other fetch handlers registered, they will get a chance to call
  // event.respondWith(). If no fetch handlers call event.respondWith(), the request will be
  // handled by the browser as if there were no service worker involvement.
});

Answer 1

I could be wrong with this one but if your user has not clicked on the Accept button, I think that is a considered Dismissed.

The only time that your user will be able to see that again is if they cleared their cache and browser settings for that particular site.

Google has also documented:

来源：https://developers.google.com/web/updates/2015/03/increasing-engagement-with-app-install-banners-in-chrome-for-android

Answer 2

您可以创建更好的用户体验，例如询问用户是否要安装应用程序，或者在某处显示安装应用程序图标，然后请求浏览器显示横幅。

现在（2018年4月）Google updated PWA documentations它显示开发者可以决定何时提示＆＃34;添加到主屏幕＆＃34;他们提供了一个示例代码。

相同的用户体验提示described here要求用户提供通知权限。

以下是他们提供的示例代码：

var deferredPrompt;

window.addEventListener('beforeinstallprompt', function(e) {
  console.log('beforeinstallprompt Event fired');
  e.preventDefault();

  // Stash the event so it can be triggered later.
  deferredPrompt = e;

  return false;
});

btnSave.addEventListener('click', function() {
  if(deferredPrompt !== undefined) {
    // The user has had a positive interaction with our app and Chrome
    // has tried to prompt previously, so let's show the prompt.
    deferredPrompt.prompt();

    // Follow what the user has done with the prompt.
    deferredPrompt.userChoice.then(function(choiceResult) {

      console.log(choiceResult.outcome);

      if(choiceResult.outcome == 'dismissed') {
        console.log('User cancelled home screen install');
      }
      else {
        console.log('User added to home screen');
      }

      // We no longer need the prompt.  Clear it up.
      deferredPrompt = null;
    });
  }
});

如果选项卡已关闭，则添加到主屏幕提示不会再次显示

2 个答案: