How to create offline HTML5 web apps in 5 easy steps

Among all cool new features introduced by HTML5, the possibility of caching web pages for offline use is definitely one of my favorites. Today, I’m glad to show you how you can create a page that will be available for offline browsing.

Getting started

• View Demo
• Download files

1 – Add HTML5 doctype

The first thing to do is create a valid HTML5 document. The HTML5 doctype is easier to remember than ones used for xhtml:

<!DOCTYPE html>
<html>
  ...

Create a file named index.html, or get the example files from my CSS3 media queries article to use as a basis for this tutorial.
In case you need it, the full HTML5 specs are available on the W3C website.

2 – Add .htaccess support

The file we’re going to create to cache our web page is called a manifest file. Before creating it, we first have to add a directive to the .htaccess file (assuming your server is Apache).

Open the .htaccess file, which is located on your website root, and add the following code:

AddType text/cache-manifest .manifest

This directive makes sure that every .manifest file is served as text/cache-manifest. If the file isn’t, then the whole manifest will have no effect and the page will not be available offline.

3 – Create the manifest file

Now, things are going to be more interesting as we create a manifest file. Create a new file and save it as offline.manifest. Then, paste the following code in it. I’ll explain it later.

CACHE MANIFEST
#This is a comment

CACHE
index.html
style.css
image.jpg
image-med.jpg
image-small.jpg
notre-dame.jpg

Right now, you have a perfectly working manifest file. The way it works is very simple: After the CACHE declaration, you have to list each files you want to make available offline. That’s enough for caching a simple web page like the one from my example, but HTML5 caching has other interesting possibilities.

For example, consider the following manifest file:

CACHE MANIFEST
#This is a comment

CACHE
index.html
style.css

NETWORK:
search.php
login.php

FALLBACK:
/api offline.html

Like in the example manifest file, we have a CACHE declaration that caches index.html and style.css. But we also have the NETWORK declaration, which is used to specify files that shouldn’t be cached, such as a login page.

The last declaration is FALLBACK. This declaration allows you to redirect the user to a particular file (in this example, offline.html) if a resource (/api) isn’t available offline.

4 – Link your manifest file to the html document

Now, both your manifest file and your main html document are ready. The only thing you still have to do is to link the manifest file to the html document.

Doing this is easy: simply add the manifest attribute to the html element as shown below:

<html manifest="/offline.manifest">

5 – Test it

Once done, you’re ready to go. If you visit your index.html file with Firefox 3.5+, you should see a banner like this one:

Other browser I’ve tested (Chrome, Safari, Android and iPhone) do not warn about the file caching, and the file is automatically cached.

Below you’ll find the browser compatibility of this technique: As usual Internet Explorer does not support it.

• IE: No support
• Firefox: 3.5+
• Safari: 4.0+
• Chrome: 5.0+
• Opera: 10.6+
• iPhone: 2.1+
• Android: 2.0+

Source: http://www.catswhocode.com/blog/how-to-create-offline-html5-web-apps-in-5-easy-steps