Going Offline

The first thing you need to run a web application offline is the ability to start it without an Internet connection. This is the purpose of the LocalServer module.

The LocalServer API and the manifest file are the key components that cache your application's resources and make it available offline.

Storing User's Data

Applications that are more than just static files have data that is typically stored on the server. For the application to be useful offline, this data must be accessible locally. The Database module provides a relational database for storing data.

When an offline application reconnects, you will need to synchronize any changes made in the local database with the server. There are many different approaches to synchronizing data, and there is no single perfect approach.

An additional feature of the Google Gears database is Full-Text Search, providing a fast way to search text within a database file.

Performance

When synchronizing large amounts of data, you may find that the database operations begin to affect the responsiveness of the browser. The WorkerPool allows you to move your database operations to the background to keep the browser responsive.

Google Gears Installation

Your web application needs to detect whether or not Google Gears is installed on a user's machine before calling the APIs, and also to determine when to display an installation prompt to the user.

Always initialize Google Gears using gears_init.js . If Gears is installed, then google.gears will be defined. If Gears isn't installed, you can direct the user to a customized installation page, as shown below.

Note: Always use gears_init.js to access Gears. Other uses may not be supported in the future.

<script src="gears_init.js"></script>
<script>
  if (!window.google || !google.gears) {
    location.href = "http://gears.google.com/?action=install&message=<your welcome message>" +
                    "&return=<your website url>";
  }
</script>

Use the URL in the code above to access the Google Gears installation page. Substitute your customized message and your URL in the parameters.

Parameters:

• action: Include the 'action' parameter with the value 'install' to cause the Google Gears installation page to use the messagereturn parameters. and
• message: Provide any text up to 150 characters. This message appears at the top of the installation page. For example: "Install Google Gears to enable MyGreatApp's offline features!"
• return: Provide your application's URL. The user will be directed back to this URL when installation is complete.