I have ready app in my launchpad downloaded with fiori app library, but it does not come up to expectations and I have to add new functionalities. Question, can it be done and how, if i want to do it in WebIDE?
that is a good question. Most of the SAP Fiori Apps have so called “Extension Points”. These extension points are also listed in the Fiori apps ref lib. They work similar like user Exits. Within the WebIDE you need to create an “Extension Project”, select your specific app, and you can start hooking into those Extension Point adding your new functionality.
Just FYI: If you just want to change some fields etc many apps also leverage the UI5 Flexibility which allows you to dose These changes even at runtime.