I’m not used to have so many callbacks spread all around the code and I’m still getting used to the idea that they aren’t executed until the event actually happens! I often find myself looking at a piece of code and not understanding how it can possibly work because I’m assuming that the function passed in is executed immediately when in fact it isn’t.

If you make a web request the response comes back in chunks so the callback we setup to capture the response will be called multiple times with different parts of the response message. For example I have this code to call Twitter and return all my friends' status updates: _~javascript var sys = require("sys"), http = require('http') exports.getTweets = function(callBack) { var twitter = http.createClient(80, "www.twitter.com"); var request = twitter.request("GET", "/statuses/friends_timeline.json", {"host": "www.twitter.com", "Authorization" : "Basic " + "xxx"}); request.addListener('response', function (response) { var tweets = ""; response.addListener("data", function (chunk) { tweets += chunk; }); response.addListener("end", function() { callBack.call(this, tweets); }); }); request.close(); }; _~ I originally thought that the listener for 'data' would only be called once but it gets called 8 times sometimes so that I’ve created the 'tweets' variable which allows us to wait until we have the full response before firing the callback when the 'end' event is fired. I’m not sure whether I’m missing the point a bit by doing this and I think I possibly need to get more used to designing functions which can deal with streams rather than expecting to have all of the data.

It seems like node.js would be perfect for a version of my colleagues Julio Maia and Fabio Lessa’s http-impersonator which is a Java application used to record and replay requests/responses made across http-based protocols. I haven’t quite worked out the best way to test the above code - ideally I want to stub out the HTTP request so that the test doesn’t have to go across the wire. Micheil Smith pointed me towards fakeweb which allows the faking of HTTP requests/responses in Ruby so I’ll probably have a go at creating something similar.