how to use ajax with json in ruby on rails?

What is the best approach for developing nimble and responsive mobile apps that will run on any platform (iPhone, iPad, Android, Kindle Fire, Blackberry, laptop)?

• My plan is to just have a web page with the user can display on any device and have all the bells and whistles implemented with javascript so that the website feels like a native app.  Is this feasible?  At least for the first draft I will not need to use anything like location services or the compass or gyroscope.  I just want an app that is responsive and feels zippy, but that I don't have to re-code with three different technologies.  Can I use AJAX for this?  Is there something better? I'm planning to do the server side with Ruby on Rails.

• Answer:

  I'd suggest using a JavaScript framework called Sencha Touch. Its a full featured, (largely) platform independent multitouch JavaScript library. That said, it doesn't support Kindle Fire. But the library is constantly evolving and will likely be compatible with other devices in the future. There are other libraries out there are well such as Dojo Touch or possibly jQuery touch (the beginnings of Sencha touch). Note that any of these don't depend on your choice of server side languages. To target laptops, you'd be better off using your traditional site. To develop the quickest, most responsive, completely platform independent app consider using plain HTML and CSS. There won't be any multitouch, but you can certainly mimic the look of a native mobile app.