<p>We are developing a considerably big application using Ruby on Rails framework (CRM system) and are considering to rewrite it to use ExtJS so that Rails would just do the data handling, while ExtJS would do all the browser heavylifting in a desktop-like manner. </p>

<p>Anyone has some experience and hints about what would be the best approach? Is ExtJS mature enough to be used in relatively big (and complex) applications? And what about the Rails part - what would be the best approach here?</p>

<p>EDIT:</p>

<p>Just to make it clear. I would prefer to do it in such a way that all the javascript client side application code is loaded at once (at the start up of the application, optimally as one compressed js file) and then just use ajax to send data to and from Rails app. Also, it would be nice to have ERB available for dynamic generation of the Ext apliccation elements.</p>

Ext is definitely mature enough to handle this situation. I'm currently working on a Rails project with a lot of Ext, and the hardest part has definitely been working with Rails's
```
to_json
```
to render JSON that Ext can read (for arrays, hashes, models, which failed validation, etc.)
Check out the ext_
```
scaffold
```
plugin for Rails. I started with this and hacked away at its
```
ActiveRecord
```
/
```
ActionView
```
extensions until it did what I needed it to do.