That information is correct, but totally irrelevant. Mech has no support for JavaScript, but the server doesn't know that. If you wanted to actually execute some JavaScript code, Mech can't do it, but all you want to do is talk to the server as if you were a browser (with JavaScript), and Mech can do that.

There is nothing that JavaScript can make a browser send to the server that you can't mimic with Mech. The only hard part is figuring out exactly what the JavaScript would send, and using HTTP::Recorder with your browser (or using some other means of looking at the requests, like LiveHTTPHeaders) solves that for you.