I’ve long been a fan of MozRepl, a Firefox plugin which allows you to open a REPL in your running Firefox that you can connect to via a socket. Why would you want to do a crazy thing like that, you ask? Mainly for the Emacs integration. Here’s the scenario:

1. Load page in browser.
2. Start MozRepl in Firefox.
3. Connect to MozRepl from the Emacs you’re editing the page’s JavaScript in.
4. Exercise some functionality on the page.
5. Find out that some function doesn’t work.
6. Make a change to the relevant JS function.
7. C-M-x
8. Return to step 4.

Notice how we don’t have to redeploy the JavaScript in question, nor hit reload in the browser?¹ This is rad. As I’ve been playing with node.js, I’ve found myself wanting the same functionality for live-tweaking my node applications during development.

Node ships with a node-repl command, which you could run as an inferior process in Emacs. The problem is that you then have to invoke your server code from within the inferior REPL, so your sever will only live as long as your Emacs process.²

What I’d really like is for the Node REPL to listen on a socket for connections from Emacs; that way, I could use MozRepl’s moz.el to talk to Node directly. Unfortunately, Node’s REPL implementation assumes it speaks to the user via stdin, stdout, and stderr, as provided in its process.stdio object.

So I built an object that pretends to be process.stdio but is actually a socket. I figured a quick process.stdio = new SocketStdio(); before my var repl = require('repl'); should do the trick. Alas, this breaks things rather thoroughly.

more

Notes

1. Sure, you say, but I can do that today with straight Firebug. Yes and no. You could cut and paste the updated code from Emacs into your Firebug prompt, but that’s ugly. ↩
2. I suppose you could use detachtty to get around this, if you really wanted to. ↩