Thanks in advance!
First you need to generate source maps when compiling the coffeescript. You can do that by passing
-m to the compiler.
The second thing you need to do, is to set break points to xhr calls. In Chrome you can find that option in the Sources tab, in the right panel, there is an option called XHR Breakpoints.
Once the XHR is fired, the browser is going to show the line of coffesscript that made the request.