How To Debug js code in the board?

Just updated with this build.

Is quit / q / Ctlr-c in debug> like 'kill process'?

Yes. The idea is that the Web IDE will be able to get out of debug mode automatically with repeated Ctrl-C. You don't want to get into trouble if you click 'upload' while debugging.

would prefer statement rather than line

This is just what node.js did. It's probably not too painful to change it.

Is p expression in debug> mode the same as expresson in normal console/non debug mode?

Basically - you just have to prefix it with p. It's like GDB (ish).

What a bout a non-quitting command to get the stack trace as well?

Not possible right now :(

What about return / r to go to the end of a function

In GDB that's called finish. I added it in the last update.

What about having the context (this) set in special 'register' and queryable?

You can do p this, but it won't show the top of the scope. In GDB that's info locals, so adding an 'info' command might be cool. To be honest querying the whole scope chain would be good.