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Friday, October 15, 2010

Where does node.js figure in the typical web application stack?

I have been reading up about node.js for a little while now. Now having Javascript as one of my favorite languages I obviously love node.js. It's simply awesome. But it was not until very recently that I started to wonder where would this node.js fit in the typical three-tier web architecture, fondly know as "the stack". The three elements of the stack being Web server, app server and DB (DB is definitely out of question). Within the app server we typically have a language interpreter and a framework (like rails).

I initially thought of node.js as a JS interpreter (similar to the ruby interpreter) and can be used with FCGI. But then again node.js in turn uses the V8 JS engine. So it's not a language interpreter per say. Then I saw several node.js examples showing how easily web based applications can be created. So I started comparing it with other frameworks like Rails or Erlyweb. But no, its not that either. Sure there is a simple HTTP module in node.js but it's in no way anywhere close to these frameworks. So is it a web server then? Definitely not that either, considering the rich feature list of existing web servers like Apache or Nginx. So what is this node.js then?

From what I have understood till now, node.js is just a JS library (not like jQuery or Prototype which are meant to run in the browser context). node.js is more like a ECMA-Script library. If we treat JS as a generic programming language, I believe, we will see quite a few shortcomings, the most significant one being the lack of system i/o facility. I guess ECMAScript was designed to be run in a host environment and hence features like console i/o or file i/o or network i/o were not added. This makes it very hard for JS to be used outside the host environment. This is exactly what node.js provides.

node.js extends the ECMA script and provides these missing aspects which enable JS to be used on the server side for network programming. node.js provides file i/o, socket i/o, process handling, a mechanism for creating modules and specifying dependencies, several network oriented modules and so on. (The complete list is here).

So node.js is really a library, which adds capabilities, although these features are somewhat at a more basic level than the ones provided other libraries. For instance, look at the libxml library in C. The C language compilers come with their own standard library which provides mechanisms to do file i/o. But there is no out of the box provision to deal with XML files/documents. This capability is provided by the libxml library. So the libxml library allows programmers to do something more with C than what is provided by default. There are innumerable number of such libraries which add various types of capabilities.

In somewhat analogous way, node.js is also a library which adds a lot of new capabilities to the Javascript language, although, as stated earlier, these capabilities are much more basic in nature and in most cases are present in other languages as part of their standard offering.

  • So node.js is not a new language and hence do not compare it with other languages like Ruby, Python, etc. Javascript is the language here.
  • node.js is not a new web application framework. So do not compare it with Rails, Django, Sinatra etc. albeit, note that node.js was apparently developed as a means to write high performance client server programs. Consequently smart folks out there started working on web application frameworks based on node and there are a couple. I know about "Express" which AFAIK, is based on Sinatra and is gaining popularity. Now that is an item comparable to Rails and friends. Questions like will node.js replace rails are, technically speaking, absurd.
  • node.js is not a server. Absolutely not. There are node.js based servers, just like Nginx and Apache are C based servers.

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