Question

我试图显示添加到主屏幕的横幅，我安装了service-worker和manifest，尝试了this，但没有显示横幅。

这是我的代码：

index.php

<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
<link rel="manifest" crossorigin="use-credentials"  href="manifest.json">
</head>
<body>

<h1>This is a Heading</h1>
<p>This is a paragraph.</p>

</body>

<script>
 if ('serviceWorker' in navigator) {
    console.log("Will the service worker register?");
    navigator.serviceWorker.register('service-worker.js')
      .then(function(reg){
        console.log("Yes, it did.");
     }).catch(function(err) {
        console.log("No it didn't. This happened:", err)
    });
 }
</script>

</html>

manifest.json

{
    "short_name": "BetaPage",
    "name": "BetaPage",
    "theme_color": "#4A90E2",
    "background_color": "#F7F8F9",
    "display": "standalone",
    "icons": [
      {
        "src": "img/apple.png",
        "type": "image/png",
        "sizes": "48x48"
      },
      {
        "src": "img/grapes.png",
        "type": "image/png",
        "sizes": "96x96"
      },
      {
        "src": "img/lemon.png",
        "type": "image/png",
        "sizes": "144x144"
      },
      {
        "src": "img/orange.png",
        "type": "image/png",
        "sizes": "192x192"
      }
    ],
    "start_url": "index.php"
  }

service-worker.js

self.addEventListener('install', function(event) {
    console.log("installed");
});

self.addEventListener('activate', function(event) {
      // Perform some task
    console.log("activated");
    });

self.addEventListener('fetch', function(event) {
    console.log("fetched");
      event.respondWith(
        fetch(event.request).catch(function() {
          return caches.match(event.request);
        })
      );
    });

但是仍然没有显示横幅，我的清单上没有错误。