Ext JS 2.0.2 to 4.x Migration

[hctong1120]

I have a web application using extjs 2.x and now I would like to upgrade to extjs 4.x

Is it extjs 2.x not compatible with extjs 4.x and do I need to rewrite the web application?

Any release note / web page show the difference between Ext JS 2.x / 4.x ?

[Gary Schlosberg]

That's a pretty major jump in versions. To make use of what Ext 4 has to offer, you will be rewriting a lot of code. There are no 2.x to 4.x upgrade guides, but here are some links that might be useful:
http://www.sencha.com/forum/showthread.php?70352-Upgrading-to-Ext-3
http://www.sencha.com/blog/ext-js-3-to-4-migration/
http://docs.sencha.com/extjs/4.1.0/#!/guide/upgrade_41
http://docs.sencha.com/extjs/4.2.0/#!/guide/upgrade_42