When I first heard about NodeJS, my reaction was, "Why would I use JavaScript on the server when there are similar continuation-passing-style, asynchronous network servers such as Twisted and Tornado in Python already? Python is a nicer language. Furthermore, I prefer coroutine-based solutions such as gevent and Concurrence." However, after watching this video , Ryan Dahl, the author of NodeJS, has convinced me that NodeJS is worthy of attention.First of all, NodeJS is crazy fast. Dahl showed one benchmark that had it beating out Nginx. (However, as he admitted, it was an unfair comparison since he was comparing NodeJS serving something out of memory with Nginx serving something from disk.) It's faster than Twisted and Jetty. That last one surprised me.Dahl argued against green thread systems and coroutine-based systems due to the infrastructural overhead and magic involved. He argued that he doesn't like Eventlet because it's too magical both at an implementation level and also because he doesn't like multiple stacks. As I said, I'm not at all convinced by his arguments, but it reassures me that he was at least able to talk about such approaches. When I brought them up during Douglas Crockford's talk on concurrency, Crockford just gave me a blank, dismissive stare.Dahl argued that by using callbacks for all blocking calls, it's really obvious which functions can block. As much as I dislike "continuation-passing-style", he makes a good point.Dahl argued that NodeJS has an advantage over EventMachine (in Ruby) and Twisted (in Python) because JavaScript programmers are inherently comfortable with event-based programming. Dahl also argued that JavaScript is well suited to event-based programming because it has anonymous functions and closures. Ruby and Python has those things too, but Dahl further argued that it's very easy to accidentally call something in Ruby or Python that is blocking since it's not easy to know if something blocks or not. In contrast, NodeJS is built from the ground up so that pretty much everything is non-blocking.NodeJS has built in support for doing DNS asynchronously, and it supports TLS (i.e. SSL). It also supports advanced HTTP features such as pipelining, chunked encoding, etc.NodeJS has an internal thread pool for making things like file I/O non-blocking. That was a bit of a surprise since I wasn't even sure it could do file I/O. The thread pool is only accessible from C since he doesn't feel most programmers can be trusted with threads. He feels most programmers should only be trusted with the asynchronous JavaScript layer which is harder to screw up.Dahl still feels that it's important to put NodeJS behind a stable web server such as Nginx. He admits that NodeJS has lots of bugs and that it's not stable. He's not at all certain that it's free of security vulnerabilities.In general, Dahl believes you'll only need one process running NodeJS per machine since it is so good at not blocking. However, it makes sense to use one process per core. It also makes sense to use multiple processes when you need to do heavy CPU crunching. At some point in the future, he hopes to add web workers a la HTML5.NodeJS has a REPL.Dealing with binary in NodeJS is non-optimal because dealing with binary in JavaScript sucks. NodeJS has a buffer class that sits outside V8. V8's memory management makes it impossible to expose pointers since memory may be moved around the heap by the garbage collector. Dahl would prefer to deal with binary in a string, but that's not currently possible. Furthermore, pushing a big string to a socket is currently slow.Dahl works for Joyent.Although I still feel Erlang has a real edge in the realm of asynchronous network servers, Erlang is difficult for most programmers to adapt to. I think NodeJS is interesting because it opens up asynchronous network programming to a much wider audience of programmers. It's also interesting because it allows you to use the same programming language and in some cases the same libraries on both the client and the server. I'm currently looking at NodeJS because I want to use socket.io for Comet aka "real time" programming. Only time will tell how NodeJS works out in practice.