HTML

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <meta name="color-scheme" content="dark light" />
    <link rel="manifest" href="manifest.json" />
    <title>How to add Richer Install UI to your web app</title>
    <!-- TODO: Devsite - Removed inline handlers -->
    <!-- <script>
      if ('serviceWorker' in navigator) {
        window.addEventListener('load', () => {
          navigator.serviceWorker.register('sw.js');
        });
      }
    </script>
    <script type="module" src="script.js"></script> -->
  </head>
  <body>
    <h1>How to add Richer Install UI to your web app</h1>
    <ol>
      <li>
        Install the app by clicking the button below. After the installation,
        the button is disabled.
        <p>
          <button disabled type="button">Install</button>
        </p>
      </li>
      <li>
        When you click on install a dialog similar to the ones from app stores
        will be displayed.
      </li>
      <li>
        The dialog includes the `description` and `screenshots` set in the app
        manifest.
      </li>
      <li>
        Screenshots should be different depending if the app is being installed
        on a mobile or desktop device, according to the `form_factor` value set
        for the screenshots on the manifest
      </li>
    </ol>
  </body>
</html>

JS


        // The install button.
const installButton = document.querySelector('button');

// Only relevant for browsers that support installation.
if ('BeforeInstallPromptEvent' in window) {
  // Variable to stash the `BeforeInstallPromptEvent`.
  let installEvent = null;

  // Function that will be run when the app is installed.
  const onInstall = () => {
    // Disable the install button.
    installButton.disabled = true;
    // No longer needed.
    installEvent = null;
  };

  window.addEventListener('beforeinstallprompt', (event) => {
    // Do not show the install prompt quite yet.
    event.preventDefault();
    // Stash the `BeforeInstallPromptEvent` for later.
    installEvent = event;
    // Enable the install button.
    installButton.disabled = false;
  });

  installButton.addEventListener('click', async () => {
    // If there is no stashed `BeforeInstallPromptEvent`, return.
    if (!installEvent) {
      return;
    }
    // Use the stashed `BeforeInstallPromptEvent` to prompt the user.
    installEvent.prompt();
    const result = await installEvent.userChoice;
    // If the user installs the app, run `onInstall()`.
    if (result.outcome === 'accepted') {
      onInstall();
    }
  });

  // The user can decide to ignore the install button
  // and just use the browser prompt directly. In this case
  // likewise run `onInstall()`.
  window.addEventListener('appinstalled', () => {
    onInstall();
  });
}