This question seems to be asked virtually every week :/
Anywho, Construct 2 is an 'event-driven' 2D game creation system that can be expanded upon by using the Java Script SDK to create plugins.
So to answer your questions directly: no, you cannot directly edit in JS in the IDE, but you can create a plugin using the SDK using JS.
The output is obfuscated Java Script, so that cannot really be edited either.