Flutter web app initialisation with loading animation

3 min readApr 14, 2023

Flutter web is great once its loaded, till the time its loaded by default they show a white screen which gives very slow feeling. So if you are in the same page where I am, We can start.

Sample gif what it will be like.

Initial Code whats inside “/web/index.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`.
  -->
  <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="flutter_test">
  <link rel="apple-touch-icon" href="icons/Icon-192.png">

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

  <title>Flutter Test</title>
  <link rel="manifest" href="manifest.json">

  <script>
    // The value below is injected by flutter build, do not touch.
    var serviceWorkerVersion = null;
  </script>
  <!-- This script adds the flutter initialization JS code -->
  <script src="flutter.js" defer></script>
</head>
<body>
  <script>
    window.addEventListener('load', function(ev) {
      // Download main.dart.js
      _flutter.loader.loadEntrypoint({
        serviceWorker: {
          serviceWorkerVersion: serviceWorkerVersion,
        }
      }).then(function(engineInitializer) {
        return engineInitializer.initializeEngine();
      }).then(function(appRunner) {
        return appRunner.runApp();
      });
    });
  </script>
</body>
</html>

Just you need to replace above code with the following code.

<!DOCTYPE html>
<html>
<head>
  <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="flutter_test">
  <link rel="apple-touch-icon" href="icons/Icon-192.png">

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

  <title>Flutter Test</title>
  <link rel="manifest" href="manifest.json">

  <script>
    // The value below is injected by flutter build, do not touch.
    var serviceWorkerVersion = null;
  </script>
  <!-- This script adds the flutter initialization JS code -->
  <script src="flutter.js" defer></script>
</head>
<body>
<style>
    body {
      background-color: #FFFFFF;
    }
</style>
<div>
  <style>
      @keyframes fadein {
        0% {
          opacity: 0
        }

        to {
          opacity: 1
        }
      }

      .container {
        align-items: center;
        display: flex;
        justify-content: space-between;
        position: relative;
        top: 1px;
        margin: 0 auto;
        max-width: calc(1280px - 100px);
        width: calc(100% - 24px*2);
      }

      .container p {
        max-width: 1200px;
        margin: 0;
        margin-right: 50px;
        color: #4a4a4a;
        font-size: 16px;
        font-family: "Roboto", sans-serif;
        line-height: 1.5;

      }

      p a {
        color: #0468d7;
        text-decoration: none;
      }

    </style>
</div>
<script>
  </script>

<!-- Loading indicator -->
<div id="loading">
  <style>
      body {
        inset: 0;
        overflow: hidden;
        margin: 0;
        padding: 0;
        position: fixed;
      }

      #loading {
        align-items: center;
        display: flex;
        height: 100%;
        justify-content: center;
        width: 100%;
      }

      #loading img {
        animation: 1s ease-in-out 0s infinite alternate breathe;
        opacity: .66;
        transition: opacity .4s;
      }

      #loading.main_done img {
        opacity: 1;
      }

      #loading.init_done img {
        animation: .33s ease-in-out 0s 1 forwards zooooom;
        opacity: .05;
      }

      @keyframes breathe {
        from {
          transform: scale(1)
        }

        to {
          transform: scale(0.95)
        }
      }

      @keyframes zooooom {
        from {
          transform: scale(1)
        }

        to {
          transform: scale(10)
        }
      }
    </style>
  <img src="icons/Icon-192.png" alt="Loading indicator..." />
</div>
<script>
    window.addEventListener('load', function () {
      var loading = document.querySelector('#loading');
      _flutter.loader.loadEntrypoint({
        serviceWorker: {
          serviceWorkerVersion: serviceWorkerVersion,
        }
      }).then(function (engineInitializer) {
        loading.classList.add('main_done');
        return engineInitializer.initializeEngine();
      }).then(function (appRunner) {
        loading.classList.add('init_done');
        return appRunner.runApp();
      }).then(function (app) {
        // Wait a few milliseconds so users can see the "zoooom" animation
        // before getting rid of the "loading" div.
        window.setTimeout(function () {
          loading.remove();
        }, 200);
      });
    });
  </script>
</body>
</html>

And Its done, You are free from old boring white page while loading.

You can set your own logo by replacing “/web/icon/Icon-192.png”
and you can replace also the favicon “/web/fevicon.png”

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Flutter web app initialisation with loading animation

Written by Rahul Dev