Okay, so playButtone is the parent, and the code, here is the code:
var button = upTo(evt.target, ".playButtone");
the code is starting from initiale, which we know is inside of playButtone, and is using upTo to find playButtone.
It should work, but it doesn't. button is left as being undefined, so what's going wrong?
The debugger has tools that can help us with this. You'll see the stepping tools above the callstack panel, that lets you play the code, step over a function, and step into a function.
In this case we want to step in to the upTo function.