Timeline actionscript vs class constructor

i inherited some movieclips on stage with a class definition called CustomShape.as. I’d like to customize each of the movieclips on stage by defining initial behaviors and i did it by entering the movieclip and entering actionscript on the first frame of the timeline. it’s not working, i reckon the constructor of the CustomShape class is overriding everything in the timeline that i wrote.

Which does execute first? the timeline code? or the class file constructor code?