Open Source GPL Sencha Ext JS 4.0 vs Commercial
I have an idea for a commercial SaaS application which I would like to build using Sencha's Ext JS framework. I understand the need to pay for a commercial license before turning around and selling the application I built using ext js, but I'm curious why it's necessary to pay for the license during the development process. I would think it's okay to build and test the application, see if it's feasible and if there is a market for it, and then pay for the license before actually selling it.
http://www.sencha.com/products/extjs/download?page=a
When to use the commercial version
If you’re going to build a commercial application with Sencha Products, you must write your application code under the commercial license from the beginning of the application development process.
And on top of that, not that I'm planning on doing this but is there any way that Sencha would know if I developed my app using Ext JS without a license and then purchased one before actually selling it?
Answer
This is more a formal matter... all code that you write under the GPL (and if you have not arranged some other license, you still have all the GPL permissions) is subject to the GPL's terms. You have permission to redistribute the code, whether by itself or as part of your own product, provided you also make the source code available to the same people under the same GPL terms.
but is there any way that Sencha would know if I developed my app using Ext JS without a license and then purchased one before actually selling it?
No! It is just restricted through the GPL license. I also started development with the GPL before I bought a proprietary license. No one will know this later on as long as you are doing all in private.