Le Domande Sencha Open Source trattano questo caso d'uso.
Ci sono 2 punti importanti:
Innanzitutto, sia il front end che il back-end sono probabili opere derivate per la GPL come in questo esempio dalle FAQ:
Example
For example: let’s take a mortgage processing software program. Let’s say that the application has a front-end (that generates web pages linked to Ext JS JavaScript) that communicates over JSON/HTTP with a backend service. This backend service contains approval and validation logic for this application alone. Even if only the front-end uses Ext JS code, you should consider that the combination of front and back ends constitutes the application, and the source code for both back and front end would need to be provided to the application’s end users under GPLv3
In secondo luogo, poiché ExtJS viene eseguito sul client che considerano l'utilizzo dell'app Conveyance:
Conveyance vs. Propagation
Since Ext JS, Sencha GXT and Sencha Touch are software programs that can run within the browser while disconnected from the network or the rest of a server program; when a Sencha based interface is embedded in a web-page served to a user who does not have an employee relationship with the original licensed entity, we consider that “conveyance” rather than simple web page “propagation” as defined by the GPL v3 has occurred, and the source code of the whole application must be provided to the user.
Quindi dovrai rendere disponibile la fonte agli utenti dell'applicazione. (Molto simile al AGPL .)
Mi è chiaro leggendo le loro FAQ che se intendi utilizzare ExtJS in un'app commerciale, vuoi che tu acquisti una licenza commerciale.