What is node.js?

Question

I don't fully get what node.js is all about. Maybe it's because I am mainly a web based business app developer. Can someone please explain what it is and the use of it? Thanks.

My understanding so far is that:

1. The programming model is event driven, especially the way it handles IO.
2. It uses javascript and the parser is V8.
3. It can be easily used to create concurrent server apps.

Are my understandings correct? If yes, then what are the benefits of evented IO, is it just more for the concurrency stuffs? Also is the direction of node.js to become a framework like, javascript based (v8 based) programming model?

Answer 1

Well, I understand that

• Node's goal is to provide an easy way to build scalable network programs.
• Node is similar in design to and influenced by systems like Ruby's Event Machine or Python's Twisted.
• Evented I/O for V8 javascript.

For me that means that you were correct in all three assumptions. The library sure looks promising!

Answer 2

v8 is an implementation of javascript, it lets you run standalone javascript apps (among other things).

node.js is simply a library written for v8 which does evented I/O. This concept is a bit trickier to explain and I'm sure someone will answer with a better explanation than I... The gist is that rather than doing some input or output and waiting for it to happen, you just don't wait for it to finish. So for example, ask for the last edited time of a file:

// pseudo code
stat( 'somefile' )

That might take a couple milliseconds, or it might take seconds. With evented IO you simply fire off the request and instead of waiting around you attach a callback that gets run when the request finishes:

// pseudo code
stat( 'somefile', function( result ) {
  // use the result here
} );
// ...more code here

This makes it a lot like javascript in the browser (eg, with Ajax style functionality).

For more information you should check out this article which was my introduction to the library/platform... I found it quite good.

Answer 3

I think the advantages are:

1. Web development in a dynamic language (JavaScript) on a VM that is incredibly fast (V8). It is much faster than Ruby, Python, or Perl.

2. Ability to handle thousands of concurrent connections with minimal overhead on a single process.

3. JavaScript is perfect for event loops with first class function objects and closures. People already know how to use it this way having used it in the browser to respond to user initiated events.

4. A lot of people already know JavaScript, even people who do not claim to be programmers. It is arguably the most popular programming language.

5. Using JavaScript on a web server as well as the browser reduces the impedance mismatch between the two programming environments which can communicate data structures via JSON that work the same on both sides of the equation. Duplicate form validation code can be shared between server and client, etc.

Answer 4

The closures are a way to execute code in the context it was created in.

what this means for concurency is that you can define variables, then initiate a nonblocking IO funciton, and send it an anonymous function for it's callback.

when the task is complete, the callback function will execute in the context with the variables, this is the closure.

The reason closures are so good for writing apps with nonblocking IO is that it's very easy to manage the context of functions executing asynchronously.