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<!DOCTYPE html><html><head><title>Express - guide</title><link rel="stylesheet" href="style.css"><link rel="stylesheet" href="//,400,600,700&amp;subset=latin,latin-ext"><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><script src=""></script><script src="app.js"></script><script src="retina.js"></script></head><body class="inner"><div class="bar"></div><section id="content"><header><section id="logo"><span class="express">express<em>3.0.0</em></span><span class="description">
web application framework for <a href="">node </a></span></section><nav class="clearfix"><a href="/" class=""> Home</a><a href="/api.html" class=""> API Reference</a><a href="/guide.html" class="active"> Guide</a><a href="/applications.html" class=""> Applications</a><a href="/community.html" class=""> Community</a><a href="/faq.html" class=""> FAQ</a></nav></header><ul id="menu"><li><ul><li><a href="#intro">Getting started</a></li><li><a href="#executable">express(1) executable</a></li><li><a href="#error-handling">Error handling</a></li></ul></li></ul><section><h3 id="intro">Getting started</h3><p>With node installed (<a href="">download</a>),
get your first application started by creating a directory somewhere
on your machine:
</p><pre class="js"><code>$ mkdir hello-world
</code></pre><p>In this same directory you'll be defining the application "package", which
are no different than any other node package. You'll need a package.json
file in the directory, with express defined as a dependency. You may use
<code>npm info express version</code> to fetch the latest version, it's
preferred that you do this instead of "3.x" below to prevent any future
</p><pre class="js"><code>{
"name": "hello-world",
"description": "hello world test app",
"version": "0.0.1",
"private": true,
"dependencies": {
"express": "3.x"
</code></pre><p>Now that you have a package.json file in this directory you can use
<code>npm(1)</code> to install the dependencies, in this case just
</p><pre class="js"><code>$ npm install
</code></pre><p>Once npm finishes you'll have a localized Express 3.x dependency in
the ./node_modules directory. You may verify this with <code>npm ls</code>
as shown in the following snippet displaying a tree of Express and its
own dependencies.
</p><pre class="js"><code>$ npm ls
hello-world@0.0.1 /private/tmp
└─┬ express@3.0.0beta7
├── commander@0.6.1
├─┬ connect@2.3.9
│ ├── bytes@0.1.0
│ ├── cookie@0.0.4
│ ├── crc@0.2.0
│ ├── formidable@1.0.11
│ └── qs@0.4.2
├── cookie@0.0.3
├── debug@0.7.0
├── fresh@0.1.0
├── methods@0.0.1
├── mkdirp@0.3.3
├── range-parser@0.0.4
├─┬ response-send@0.0.1
│ └── crc@0.2.0
└─┬ send@0.0.3
└── mime@1.2.6
</code></pre><p>Now to create the application itself! Create a file named app.js or server.js,
whichever you prefer, require express and then create a new application with <code>express()</code>:
</p><pre class="js"><code>var express = require('express');
var app = express();
</code></pre><p>With the new application instance you can start defining routes via <code>app.VERB()</code>,
in this case "GET /" responding with the "Hello World" string. The <code>req</code> and
<code>res</code> are the exact same objects that node provides to you, thus you may invoke
<code>res.pipe()</code>, <code>req.on('data', callback)</code> and anything else you
would do without Express involved.
</p><pre class="js"><code>app.get('/', function(req, res){
res.send('Hello World');
</code></pre><p>Now to bind and listen for connections invoke the <code>app.listen()</code> method,
accepting the same arguments as node's <a href="">net.Server#listen()</a>:
</p><pre class="js"><code>app.listen(3000);
console.log('Listening on port 3000');</code></pre></section><section><h3 id="executable">Using express(1) to generate an app</h3><p>Express is bundled with an executable, aptly named <code>express(1)</code>.
If you install express globally with npm you'll have it available from anywhere
on your machine:
</p><pre class="js"><code>$ npm install -g express
</code></pre><p>This tool provides a simple way to get an application skeleton going,
but has limited scope, for example it supports only a few template engines,
whereas Express itself supports virtually any template engine built for node.
Be sure to check out the <code>--help</code>:
</p><pre class="js"><code>Usage: express [options]
-h, --help output usage information
-V, --version output the version number
-s, --sessions add session support
-e, --ejs add ejs engine support (defaults to jade)
-J, --jshtml add jshtml engine support (defaults to jade)
-h, --hogan add hogan.js engine support
-c, --css <engine> add stylesheet <engine> support (less|stylus) (defaults to plain css)
-f, --force force on non-empty directory</code></pre><p>If you want to generate an application with EJS, Stylus, and session
support you would simply execute:
</p><pre class="js"><code>$ express --sessions --css stylus --ejs myapp
create : myapp
create : myapp/package.json
create : myapp/app.js
create : myapp/public
create : myapp/public/javascripts
create : myapp/public/images
create : myapp/public/stylesheets
create : myapp/public/stylesheets/style.styl
create : myapp/routes
create : myapp/routes/index.js
create : myapp/views
create : myapp/views/index.ejs
install dependencies:
$ cd myapp && npm install
run the app:
$ node app
</code></pre><p>Like any other node application, you must then install the dependencies:
</p><pre class="js"><code>$ cd myapp
$ npm install
</code></pre><p>Then fire it up!
</p><pre class="js"><code>$ node app
</code></pre><p>That's all you need to get a simple application up and running. Keep in mind
that Express is not bound to any specific directory structure, these are simply
a baseline for you to work from. For application structure alternatives be
sure to view the <a href="">examples</a>
found in the github repo.</p></section><section><h3 id="error-handling">Error handling</h3><p>Error-handling middleware are defined just like regular middleware,
however must be define with an arity of 4, that is the signature
<code>(err, req, res, next)</code>:
</p><pre class="js"><code>app.use(function(err, req, res, next){
res.send(500, 'Something broke!');
</code></pre><p>Though not mandatory error-handling middleware are typically defined
very last, below any other <code>app.use()</code> calls as shown here:
</p><pre class="js"><code>app.use(express.bodyParser());
app.use(function(err, req, res, next){
// logic
</code></pre><p>Responses from within these middleware are completely arbitrary. You may
wish to respond with an HTML error page, a simple message, a JSON string,
or anything else you prefer.
</p><p>For organizational, and higher-level framework purposes you may define
several of these error-handling middleware, much like you would with
regular middleware. For example suppose you wanted to define an error-handler
for requests made via XHR, and those without, you might do:
</p><pre class="js"><code>app.use(express.bodyParser());
</code></pre><p>Where the more generic <code>logErrors</code> may write request and
error information to stderr, loggly, or similar services:
</p><pre class="js"><code>function logErrors(err, req, res, next) {
</code></pre><p>Where <code>clientErrorHandler</code> is defined as the following, note
that the error is explicitly passed along to the next.
</p><pre class="js"><code>function clientErrorHandler(err, req, res, next) {
if (req.xhr) {
res.send(500, { error: 'Something blew up!' });
} else {
</code></pre><p>The following <code>errorHandler</code> "catch-all" implementation may be defined as:
</p><pre class="js"><code>function errorHandler(err, req, res, next) {
res.render('error', { error: err });
}</code></pre></section></section><script>var _gaq = _gaq || [];
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