> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/web/get-started/samples/webviewer-offline.md).

# Implement WebViewer Offline Using Service Worker and localforage

Sample to implement WebViewer offline using service worker and localforage.

This sample shows how you can load WebViewer offline using [service worker](https://developer.chrome.com/docs/workbox/service-worker-overview/) and [localforage](https://github.com/localForage/localForage).

WebViewer provides a slick out-of-the-box responsive UI that enables you to view, annotate and manipulate PDFs and other document types inside any web project.

Click the button below to view the full project in GitHub.

{% tabs %}
{% tab title="JavaScript" %}
{% code title="index.js" lineNumbers="true" %}

```js
var viewerElement = document.getElementById('viewer');

var files = [
  '/files/webviewer-demo-annotated.xod',
  '/files/webviewer-demo-annotated.pdf',
  '/files/legal-contract.docx',
];

WebViewer({
  path: '/public/lib',
  preloadWorker: WebViewer.WorkerTypes.ALL,
}, viewerElement).then(instance => {
  var store = localforage.createInstance({ name: 'store' });
  var documentsDiv = document.getElementById('documents');

  files.forEach(function(file) {
    var list = document.createElement('li');
    var div = document.createElement('div');
    var button = document.createElement('button');
    var fileName = file.split('/').slice(-1)[0];

    div.innerHTML = fileName;
    button.innerHTML = 'Open';
    button.onclick = function() {
      if (button.innerHTML === 'Open') {
        store
          .getItem(fileName)
          .then(function(blob) {
            blob.name = fileName;
            instance.UI.loadDocument(blob, { filename: fileName });
          });
      } else {
        fetch(file)
          .then(function(response) {
            return response.blob();
          })
          .then(function(blob) {
            store.setItem(fileName, blob);
            button.innerHTML = 'Open';
          })
          .catch(() => {
            console.log('Error fetching the file');
          });
      }
    };

    list.appendChild(div);
    list.appendChild(button);

    documentsDiv.appendChild(list);

    // Change button text to Open if the file is cached, otherwise set the text to Download
    store.keys().then(function(keys) {
      if (keys.indexOf(fileName) === -1) {
        button.innerHTML = 'Download';
      }
    });
  });
});

// Register service worker
if ('serviceWorker' in navigator) {
  navigator.serviceWorker.register('/serviceWorker.js')
    .then(function(registration) {
      if (registration.installing) {
        console.log('Service worker installing');
      } else if (registration.waiting) {
        console.log('Service worker installed');
      } else if (registration.active) {
        console.log('Service worker active');
      }
    }).catch(function(err) {
      console.log('ServiceWorker registration failed: ', err);
    });
} else {
  alert('This browser does not support service worker.');
}





// WPA app installer
const Installer = function(root) {
  let promptEvent;

  const install = function(e) {
    if(promptEvent) {
      promptEvent.prompt();
      promptEvent.userChoice
        .then(function(choiceResult) {
          // The user actioned the prompt (good or bad).
          // good is handled in
          promptEvent = null;
          root.classList.remove('available');
        })
        .catch(function(installError) {
          // Boo. update the UI.
          promptEvent = null;
          root.classList.remove('available');
        });
    }
  };

  const installed = function(e) {
    promptEvent = null;
    // This fires after onbeforinstallprompt OR after manual add to homescreen.
    root.classList.remove('available');
  };

  const beforeinstallprompt = function(e) {
    promptEvent = e;
    promptEvent.preventDefault();
    root.classList.add('available');
    return false;
  };

  window.addEventListener('beforeinstallprompt', beforeinstallprompt);
  window.addEventListener('appinstalled', installed);

  root.addEventListener('click', install.bind(this));
  root.addEventListener('touchend', install.bind(this));
};


window.addEventListener('load', function() {
  const installEl = document.getElementById('installer');
  const installer = new Installer(installEl);

  var headerElement = document.getElementsByTagName('header')[0];
  var asideElement = document.getElementsByTagName('aside')[0];

  var menuButton = document.createElement('div');
  menuButton.className = 'menu';
  menuButton.onclick = function() {
    if (asideElement.style.display === 'block') {
      asideElement.style.display = 'none';
    } else {
      asideElement.style.display = 'block';
    }
  };


  var div = document.createElement('div');
  menuButton.appendChild(div);
  menuButton.appendChild(div.cloneNode());
  menuButton.appendChild(div.cloneNode());

  headerElement.appendChild(menuButton);
})

```

{% endcode %}
{% endtab %}
{% endtabs %}

[View the full sample on GitHub](https://github.com/ApryseSDK/webviewer-samples/tree/main/webviewer-offline)


---

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