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<link rel="alternate"
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type="application/rss+xml"
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title="node blog"
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href="http://feeds.feedburner.com/nodejs/123123123">
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<title>node.js</title>
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<div id="intro">
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<img id="logo" src="../logo.png" alt="node.js">
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<div id="content" class="clearfix">
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<div id="column1" class="interior">
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<h2>About</h2>
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<pre>
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var http = require('http');
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http.createServer(function (req, res) {
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res.writeHead(200, {'Content-Type': 'text/plain'});
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res.end('Hello World\n');
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}).listen(1337, "127.0.0.1");
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console.log('Server running at http://127.0.0.1:1337/');</pre>
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<p>Node's goal is to provide an easy way to build scalable
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network programs. In the "hello world" web server example
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above, many client connections can be handled concurrently.
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Node tells the operating system (through <code>epoll</code>,
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<code>kqueue</code>, <code>/dev/poll</code>, or
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<code>select</code>) that it should be notified when a new
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connection is made, and then it goes to sleep. If someone new
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connects, then it executes the callback. Each connection is
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only a small heap allocation.</p>
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<p>This is in contrast to today's more common concurrency
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model where OS threads are employed. Thread-based networking
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is relatively inefficient and very difficult to use. See: <a
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href="http://www.kegel.com/c10k.html">this</a> and <a
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href="http://bulk.fefe.de/scalable-networking.pdf">this</a>.
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Node will show much better memory efficiency under high-loads
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than systems which allocate 2mb thread stacks for each
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connection. Furthermore, users of Node are free from worries
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of dead-locking the process—there are no locks. Almost no
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function in Node directly performs I/O, so the process never
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blocks. Because nothing blocks, less-than-expert programmers
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are able to develop fast systems.</p>
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<p>Node is similar in design to and influenced by systems like
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Ruby's <a href="http://rubyeventmachine.com/">Event
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Machine</a> or Python's <a
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href="http://twistedmatrix.com/">Twisted</a>. Node takes the
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event model a bit further—it presents the event loop as a
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language construct instead of as a library. In other systems
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there is always a blocking call to start the event-loop.
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Typically one defines behavior through callbacks at the
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beginning of a script and at the end starts a server through a
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blocking call like <code>EventMachine::run()</code>. In Node
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there is no such start-the-event-loop call. Node simply enters
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the event loop after executing the input script. Node exits
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the event loop when there are no more callbacks to perform.
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This behavior is like browser javascript—the event loop is
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hidden from the user.</p>
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<p>HTTP is a first class protocol in Node. Node's HTTP library
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has grown out of the author's experiences developing and
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working with web servers. For example, streaming data through
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most web frameworks is impossible. Node attempts to correct
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these problems in its HTTP <a
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href="https://github.com/joyent/http-parser/tree/master">parser</a>
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and API. Coupled with Node's purely evented infrastructure, it
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makes a good foundation for web libraries or frameworks.</p>
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<p>But what about multiple-processor concurrency? Aren't
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threads necessary to scale programs to multi-core computers?
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You can start new processes via <code><a
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href="http://nodejs.org/docs/latest/api/child_processes.html#child_process.fork">child_process.fork()</a></code>
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these other processes will be scheduled in parallel. For load
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balancing incoming connections across multiple processes use
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<a href="http://nodejs.org/docs/latest/api/cluster.html">the
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cluster module</a>.</p>
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<p>See also:</p>
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<ul>
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<li><a href="http://s3.amazonaws.com/four.livejournal/20091117/jsconf.pdf">Slides from JSConf 2009</a></li>
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<li><a href="http://nodejs.org/jsconf2010.pdf">Slides from JSConf 2010</a></li>
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<li><a href="http://www.yuiblog.com/blog/2010/05/20/video-dahl/">Video from a talk at Yahoo in May 2010</a></li>
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</ul>
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<p><a href="/">Go back to the home page</a></p>
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<p>Copyright <a href="http://joyent.com">Joyent, Inc</a>, Node.js
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is a <a href="trademark-policy.pdf">trademark of Joyent, Inc</a>.
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