* Motivation

From my experience an ability to use REPL for JavaScript debugging and
interactive development is very helpful when developing Web
applications. Previously I was using a heavily patched [[https://github.com/bard/mozrepl/wiki/][Mozrepl]] version
that was adapted for in-browser JavaScript. Primary downsides of that
approach were extreme instability of communication between Emacs and
the browser, the lack of cross-browser support and the lack of good
RPC between Emacs and JS that can be used to develop some handy
extensions.

I knew there exists [[https://github.com/3b/slime-proxy][slime-proxy]] project that provides such
functionality for [[http://common-lisp.net/project/parenscript/][Parenscript]]. The problem is that most of us
including myself can't use Lisp all the time and a lot of code needs
to be developed using languages like plain JavaScript [as opposed to
Parenscript), Python and so on. My first thought was to adapt
slime-proxy for use with plain JS, but then I decided to roll my own
SWANK backend using Node.JS. I wanted to find out what this buzz
around Node.JS is about and perhaps steal an idea or two from there
for use in my Lisp projects. Another reason was availability of
[[http://socket.io/][Socket.IO]] and an example of [[http://www.catonmat.net/http-proxy-in-nodejs][tiny http server proxy]].

Some people may prefer Firebug or built-in browser development tools
to Emacs-based development, but for example in case of mobile browsers
you don't have much choice. At some point I did try swank-js with an
colleague's iPhone and it worked, which is not too unexpected given
that Socket.IO has good cross-browser support.