深海游弋的鱼 – 默默的点滴

升级到 Flutter 3.22.0之后，在 Chrome 上运行 Flutter Web 应用程序时收到以下警告：

Launching lib/main.dart on Chrome in debug mode...
Waiting for connection from debug service on Chrome...
Warning: In index.html:40: Local variable for "serviceWorkerVersion" is deprecated. Use "{{flutter_service_worker_version}}" template token instead. See https://docs.flutter.dev/platform-integration/web/initialization for more details.

Launching lib/main.dart on Chrome in debug mode...

Waiting for connection from debug service on Chrome...

Warning: In index.html:40: Local variable for "serviceWorkerVersion" is deprecated. Use "{{flutter_service_worker_version}}" template token instead. See https://docs.flutter.dev/platform-integration/web/initialization for more details.

这个警告的原因是，新版本的 Flutter Web 应用加载 service_worker.js 的方式发生了变化，原来的加载脚本被 {{flutter_bootstrap_js}} 替代。

调整为新的初始化代码即可解决此问题。

原始的代码如下：

<!DOCTYPE html>
<html>
<head>
  <!--
    If you are serving your web app in a path other than the root, change the
    href value below to reflect the base path you are serving from.

    The path provided below has to start and end with a slash "/" in order for
    it to work correctly.

    For more details:
    * https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base

    This is a placeholder for base href that will be replaced by the value of
    the `--base-href` argument provided to `flutter build`.
  -->
  <base href="$FLUTTER_BASE_HREF">

  <meta charset="UTF-8">
  <meta content="IE=Edge" http-equiv="X-UA-Compatible">
  <meta name="description" content="A new Flutter project.">

  <!-- iOS meta tags & icons -->
  <meta name="apple-mobile-web-app-capable" content="yes">
  <meta name="apple-mobile-web-app-status-bar-style" content="black">
  <meta name="apple-mobile-web-app-title" content="xxxx">
  <link rel="apple-touch-icon" href="icons/Icon-192.png">

  <!-- Favicon -->
  <link rel="icon" type="image/png" href="favicon.png"/>

  <title>xxxx</title>
  <link rel="manifest" href="manifest.json">
</head>
<body>
  <!-- This script installs service_worker.js to provide PWA functionality to
       application. For more information, see:
       https://developers.google.com/web/fundamentals/primers/service-workers -->
  <script>
    var serviceWorkerVersion = null;
    var scriptLoaded = false;
    function loadMainDartJs() {
      if (scriptLoaded) {
        return;
      }
      scriptLoaded = true;
      var scriptTag = document.createElement('script');
      scriptTag.src = 'main.dart.js';
      scriptTag.type = 'application/javascript';
      document.body.append(scriptTag);
    }

    if ('serviceWorker' in navigator) {
      // Service workers are supported. Use them.
      window.addEventListener('load', function () {
        // Wait for registration to finish before dropping the <script> tag.
        // Otherwise, the browser will load the script multiple times,
        // potentially different versions.
        var serviceWorkerUrl = 'flutter_service_worker.js?v=' + serviceWorkerVersion;
        navigator.serviceWorker.register(serviceWorkerUrl)
          .then((reg) => {
            function waitForActivation(serviceWorker) {
              serviceWorker.addEventListener('statechange', () => {
                if (serviceWorker.state == 'activated') {
                  console.log('Installed new service worker.');
                  loadMainDartJs();
                }
              });
            }
            if (!reg.active && (reg.installing || reg.waiting)) {
              // No active web worker and we have installed or are installing
              // one for the first time. Simply wait for it to activate.
              waitForActivation(reg.installing || reg.waiting);
            } else if (!reg.active.scriptURL.endsWith(serviceWorkerVersion)) {
              // When the app updates the serviceWorkerVersion changes, so we
              // need to ask the service worker to update.
              console.log('New service worker available.');
              reg.update();
              waitForActivation(reg.installing);
            } else {
              // Existing service worker is still good.
              console.log('Loading app from service worker.');
              loadMainDartJs();
            }
          });

        // If service worker doesn't succeed in a reasonable amount of time,
        // fallback to plaint <script> tag.
        setTimeout(() => {
          if (!scriptLoaded) {
            console.warn(
              'Failed to load app from service worker. Falling back to plain <script> tag.',
            );
            loadMainDartJs();
          }
        }, 4000);
      });
    } else {
      // Service workers not supported. Just drop the <script> tag.
      loadMainDartJs();
    }
  </script>
</body>
</html>

100

101

102

103

104

<!DOCTYPE html>

<html>

<head>

<!--

If you are serving your web app in a path other than the root, change the

href value below to reflect the base path you are serving from.

The path provided below has to start and end with a slash "/" in order for

it to work correctly.

For more details:

* https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base

This is a placeholder for base href that will be replaced by the value of

the `--base-href` argument provided to `flutter build`.

-->

</head>

<body>

<!-- This script installs service_worker.js to provide PWA functionality to

application. For more information, see:

https://developers.google.com/web/fundamentals/primers/service-workers -->

var serviceWorkerVersion = null;

var scriptLoaded = false;

function loadMainDartJs() {

if (scriptLoaded) {

return;

}

scriptLoaded = true;

var scriptTag = document.createElement('script');

scriptTag.src = 'main.dart.js';

scriptTag.type = 'application/javascript';

document.body.append(scriptTag);

}

if ('serviceWorker' in navigator) {

// Service workers are supported. Use them.

window.addEventListener('load', function () {

// Wait for registration to finish before dropping the <script> tag.

// Otherwise, the browser will load the script multiple times,

// potentially different versions.

var serviceWorkerUrl = 'flutter_service_worker.js?v=' + serviceWorkerVersion;

navigator.serviceWorker.register(serviceWorkerUrl)

.then((reg) => {

function waitForActivation(serviceWorker) {

serviceWorker.addEventListener('statechange', () => {

if (serviceWorker.state == 'activated') {

console.log('Installed new service worker.');

loadMainDartJs();

}

});

}

if (!reg.active && (reg.installing || reg.waiting)) {

// No active web worker and we have installed or are installing

// one for the first time. Simply wait for it to activate.

waitForActivation(reg.installing || reg.waiting);

} else if (!reg.active.scriptURL.endsWith(serviceWorkerVersion)) {

// When the app updates the serviceWorkerVersion changes, so we

// need to ask the service worker to update.

console.log('New service worker available.');

reg.update();

waitForActivation(reg.installing);

} else {

// Existing service worker is still good.

console.log('Loading app from service worker.');

loadMainDartJs();

}

});

// If service worker doesn't succeed in a reasonable amount of time,

// fallback to plaint <script> tag.

setTimeout(() => {

if (!scriptLoaded) {

console.warn(

'Failed to load app from service worker. Falling back to plain <script> tag.',

);

loadMainDartJs();

}

}, 4000);

});

} else {

// Service workers not supported. Just drop the <script> tag.

loadMainDartJs();

}

</script>

</body>

</html>

调整后的代码如下：

<!DOCTYPE html>
<html>
<head>
  <!--
    If you are serving your web app in a path other than the root, change the
    href value below to reflect the base path you are serving from.

    The path provided below has to start and end with a slash "/" in order for
    it to work correctly.

    For more details:
    * https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base

    This is a placeholder for base href that will be replaced by the value of
    the `--base-href` argument provided to `flutter build`.
  -->
  <base href="$FLUTTER_BASE_HREF">

  <meta charset="UTF-8">
  <meta content="IE=Edge" http-equiv="X-UA-Compatible">
  <meta name="description" content="A new Flutter project.">

  <!-- iOS meta tags & icons -->
  <meta name="apple-mobile-web-app-capable" content="yes">
  <meta name="apple-mobile-web-app-status-bar-style" content="black">
  <meta name="apple-mobile-web-app-title" content="xxxx">
  <link rel="apple-touch-icon" href="icons/Icon-192.png">

  <!-- Favicon -->
  <link rel="icon" type="image/png" href="favicon.png"/>

  <title>xxxx</title>
  <link rel="manifest" href="manifest.json">
</head>
<body>
  <!-- This script installs service_worker.js to provide PWA functionality to
       application. For more information, see:
       https://developers.google.com/web/fundamentals/primers/service-workers -->
    <script>
      {{flutter_bootstrap_js}}
    </script>
</body>
</html>

<!DOCTYPE html>

<html>

<head>

<!--

If you are serving your web app in a path other than the root, change the

href value below to reflect the base path you are serving from.

The path provided below has to start and end with a slash "/" in order for

it to work correctly.

For more details:

* https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base

This is a placeholder for base href that will be replaced by the value of

the `--base-href` argument provided to `flutter build`.

-->

</head>

<body>

<!-- This script installs service_worker.js to provide PWA functionality to

application. For more information, see:

https://developers.google.com/web/fundamentals/primers/service-workers -->

</script>

</body>

</html>

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日期: 2024 年 12 月 4 日

Flutter Web 警告 Local variable for "serviceWorkerVersion" is deprecated

参考链接