There are a collection of facilities that are available to developers using HTML5 that enable an HTML5 app to run when no connection to the internet is available.

Of course, the first access to the app requires an internet connection but during that first experience the browser can use AppCache to save the required resources locally so that they are present later when a network connection is not available. Clever use of the NETWORK and FALLBACK sections help you tailor the app’s experience based on the network connection state.

Local Storage and IndexedDB provide facilities to store needed data for use both online and off. window.navigator.onLine and associated event listeners can even help you switch state at runtime.

So technology is in place for building offline HTML5 apps. At Mozilla we’re busy building an HTML5 apps run-time for running HTML5 apps on Windows, Mac,Linux and Android, a marketplace for distribution of such apps, and a cool HTML5 based phone operating system (Firefox OS).

So for the last 10 months or so I’ve been really focused on HTML5 “apps” and I’m especially excited about the B2G Phone OS but it does leave me with the question, how much do folks really need off line functionality in an HTML5 app ?

Fault Tolerant Cloud Based Hosting has become a norm in recent years and the service levels have been very reliable so the question become the utility of the proverbial “last mile”.

For mobile users there are two questions.

1.) Is there service everywhere I need there to be.

2.) How much will use effect my service plan.

Here in rural New England, where I live, there are many spots without cell service coverage. However I tend to only experience them when I’m driving in between places that DO have coverage so the inconvenience is minimal.

As to the data usage, my monthly service contract comes with a monthly data allowance. If my internet usage surpasses that allocation AT&T just automatically adds another “block” of usage to my bill for that month. (I think the increment is $20USD) – So at least it’s not like the old days when you exceeded your plan, silently went into a high-price-by-the-minute plan and got surprised by a $1,000 cell phone bill at the end of the month.

But, the way that it works in the USA and Europe is not necessarily the way it works in the resat of the world.

For example, Mozilla’s phone OS initiative is expected to launch in Brazil first (read more here) but consumer usage profiles in Brazil are very different. Something like 85% of cell phones are acquired on prepaid / pay-as-you-go contracts. This means when you run out of prepaid data access, you’re done until you buy more. Local experts also inform us that “public” use of smart phones is significantly curtailed due to theft concerns, etc.

So share your thoughts on the following two questions.

1.) How much does OFF LINE functionality matter for a desktop app?

2.) How much does OFF LINE functionality matter for a MOBILE phone or tablet app?