Guy Royse

Work. Life. Code. Game. Later. Rinse. Repeat.

Disconnected HTML5, JavaScript, the iPhone & I

I’ve been working on a simple test case for a disconnected HTML5 application for the iPhone/iTouch off and on for the past couple of weeks. It’s a points calculator for a popular weight loss program who shall remain anonymous. Anyhow, I thought this would be a handy tool for my wife and I and it would be a nice and simple application to test a disconnected HTML5 application from the iPhone.

So, I present to you Puntos. Full source code is available on github but here’s how I wrote it.

Step #1: Write an HTML5 and JavaScript Application

The application I developed is not remarkable. In fact, it is a simple math problem. Peruse the source if you want details on how it works. The important part is that it has the following files:

index.html
calculator.js
calculator.css
jquery.js

Just create the files for your application (or copy mine) and make it do what it does. I’m assuming you know how to program in JavaScript and HTML.

Step #2: Make it iPhone Friendly

If you want it to be a cool iPhone HTML5 application, you have to provide an icon from the iPhone desktop. You can do this by creating a file called iphone-icon.png and placing it in the root of you project. This little file is the favicon.ico of the Apple Mobile world. It is a 45 pixel by 45 pixel PNG that your iPhone or iTouch will use if you decided to save a link to a website on your desktop.

So, just create this file with your favorite image editing program (I used Gimp) and save it with the other files.

Step #3: Add the Caching Magic

Here’s where the fun comes in. We can finally make the application disconnected. The magic lies in an attribute on the html tag pointing the browser to a cache.manifest file. This file then tells the browser which files to cache and serve up when there isn’t a network connection.

So, simply add something like this to your HTML file.

<html manifest="cache.manifest">

This tells your browser to load up the file in the manifest attribute. The filename can be anything but I would recommend having it end in .manifest as this makes setting up the content type later much easier.

The cache.manifest is simplicity itself:

CACHE MANIFEST
calculator.js
calculator.css
jquery.js
iphone-icon.png

It simple contains the words CACHE MANIFEST at the top and lists all the files needed by the application.

You might note that I did not include the index.html and you would be correct. This is because the browser will assume that the file you loaded in the initial request is part of the cache.manifest. No need to specify. However, if you have several HTML files, you will need to specify them all in your cache.manifest as there is no way to know which file you entered the application from.

Step #4: Serving Up text/cache-manifest

It turns out that the cache.manifest file must be served up with a content type of text/cache-manifest. It also turns out that most web servers aren’t configured by default to do this since this is all bleeding edge and stuff.

So, you need to add it yourself. If you are using an apache server you can add the content type to your .htaccess file. Add the following line and you should be golden.

AddType text/cache-manifest .manifest

Step #5: Access the Application from Your iPhone & Troubleshoot

Your application should now work. So go access it. Then turn on Airplane Mode and refresh the application. I should reload gorgeously. If it doesn’t, go back and troubleshoot. But you knew that already.

One caveat though. I had a hell of a time trying to get the application to work disconnected until I rebooted my iTouch (I don’t have an iPhone because I’m lame). So, if everything looks like it should work but isn’t then you might want to try turning off your iPhone by pressing and holding the power button until it shuts down completely.

So, those are the steps I followed to get my first disconnected iPhone application working with HTML5, JavaScript, and some cache.manifest magic. Now go out and write me a game or something.

Also, for more information on HTML5 and disconnected applications check out this fine website.

— February 23, 2011