Recently, I needed to add realtime (i.e. comet, websockets, flash sockets, etc.) support to an application. Socket.IO is a library built on top of Node.JS that "aims to make realtime apps possible in every browser and mobile device, blurring the differences between the different transport mechanisms." Since Socket.IO did exactly what I needed, I was hoping it would solve my problems easily and that I wouldn't have to implement what Socket.IO did myself.
Unfortunately, things didn't work out so well. I had to do things in a cross-domain manner. Although the browser support list for Socket.IO is very good, that didn't match up with my actual experience. I built a simple application that tried to send and receive a message using Socket.IO, and then it reported on which transport was used. Unfortunately, many of the browsers that I wanted to support such as IE 6 and 7 and Opera just didn't work, even though they were supposed to. Here are some of my results.
Furthermore, if you watch the mailing list, a lot of questions just get dropped on the floor. I'm sure this is because the authors of Socket.IO are completely overwhelmed. Hopefully as Socket.IO matures and the list of expert users grows, this will improve.
By the way, you might wonder how I tested so many browsers. I paid for an account on crossbrowsertesting.com. It was worth every penny! First, I would use it to try to take a snapshot of my test page on all the different browsers. Then, I would use the web-based VNC system to log into the systems and view the page manually in order to see what was going wrong. This was very helpful to determine exactly which browsers did and didn't work.
Anyway, as I said, I hope Socket.IO gets better because it solves a real need. Perhaps it already has, since I was doing this testing several months ago. However, if you need to use Socket.IO, I heartily recommend you make use of crossbrowsertesting.com to make sure that the browsers you need to support actually work.
In my next post, I'll cover JS.IO.