Question

express()

Creates an Express application. The express() function is a top-level function exported by the express module.

var express = require('express')
var app = express()

app.get('/', function (req, res) {
  res.send('hello world')
})

app.listen(3000)

Application

app.set(name, value)

Assigns setting name to value.

app.set('title', 'My Site')
app.get('title')
// => "My Site"

app.get(name)

Get setting name value.

app.get('title')
// => undefined

app.set('title', 'My Site')
app.get('title')
// => "My Site"

app.enable(name)

Set setting name to true.

app.enable('trust proxy')
app.get('trust proxy')
// => true

app.disable(name)

Set setting name to false.

app.disable('trust proxy')
app.get('trust proxy')
// => false

app.enabled(name)

Check if setting name is enabled.

app.enabled('trust proxy')
// => false

app.enable('trust proxy')
app.enabled('trust proxy')
// => true

app.disabled(name)

Check if setting name is disabled.

app.disabled('trust proxy')
// => true

app.enable('trust proxy')
app.disabled('trust proxy')
// => false

app.configure([env], callback)

Conditionally invoke callback when env matches app.get('env'), aka process.env.NODE_ENV. This method remains for legacy reasons, and is effectively an if statement as illustrated in the following snippets. These functions are not required in order to use app.set() and other configuration methods.

// all environments
app.configure(function () {
  app.set('title', 'My Application')
})

// development only
app.configure('development', function () {
  app.set('db uri', 'localhost/dev')
})

// production only
app.configure('production', function () {
  app.set('db uri', 'n.n.n.n/prod')
})

Is effectively sugar for:

// all environments
app.set('title', 'My Application')

// development only
if (app.get('env') === 'development') {
  app.set('db uri', 'localhost/dev')
}

// production only
if (app.get('env') === 'production') {
  app.set('db uri', 'n.n.n.n/prod')
}

app.use([path], function)

Use the given middleware function, with optional mount path, defaulting to “/”.

var express = require('express')
var app = express()

// simple logger
app.use(function (req, res, next) {
  console.log('%s %s', req.method, req.url)
  next()
})

// respond
app.use(function (req, res, next) {
  res.send('Hello World')
})

app.listen(3000)

The “mount” path is stripped and is not visible to the middleware function. The main effect of this feature is that mounted middleware may operate without code changes regardless of its “prefix” pathname.

A route will match any path that follows its path immediately with either a “/” or a “.”. For example: app.use('/apple', ...) will match /apple, /apple/images, /apple/images/news, /apple.html, /apple.html.txt, and so on.

Here’s a concrete example, take the typical use-case of serving files in ./public using the express.static() middleware:

// GET /javascripts/jquery.js
// GET /style.css
// GET /favicon.ico
app.use(express.static(path.join(__dirname, 'public')))

Say for example you wanted to prefix all static files with “/static”, you could use the “mounting” feature to support this. Mounted middleware functions are not invoked unless the req.url contains this prefix, at which point it is stripped when the function is invoked. This affects this function only, subsequent middleware will see req.url with “/static” included unless they are mounted as well.

// GET /static/javascripts/jquery.js
// GET /static/style.css
// GET /static/favicon.ico
app.use('/static', express.static(path.join(__dirname, 'public')))

The order of which middleware are “defined” using app.use() is very important, they are invoked sequentially, thus this defines middleware precedence. For example usually express.logger() is the very first middleware you would use, logging every request:

app.use(express.logger())
app.use(express.static(path.join(__dirname, 'public')))
app.use(function (req, res) {
  res.send('Hello')
})

Now suppose you wanted to ignore logging requests for static files, but to continue logging routes and middleware defined after logger(), you would simply move static() above:

app.use(express.static(path.join(__dirname, 'public')))
app.use(express.logger())
app.use(function (req, res) {
  res.send('Hello')
})

Another concrete example would be serving files from multiple directories, giving precedence to “./public” over the others:

app.use(express.static(path.join(__dirname, 'public')))
app.use(express.static(path.join(__dirname, 'files')))
app.use(express.static(path.join(__dirname, 'uploads')))

settings

The following settings are provided to alter how Express will behave:

• env Environment mode, defaults to process.env.NODE_ENV or “development”
• trust proxy Enables reverse proxy support, disabled by default
• jsonp callback name Changes the default callback name of ?callback=
• json replacer JSON replacer callback, null by default
• json spaces JSON response spaces for formatting, defaults to 2 in development, 0 in production
• case sensitive routing Enable case sensitivity, disabled by default, treating “/Foo” and “/foo” as the same
• strict routing Enable strict routing, by default “/foo” and “/foo/” are treated the same by the router
• view cache Enables view template compilation caching, enabled in production by default
• view engine The default engine extension to use when omitted
• views The view directory path, defaulting to “process.cwd() + ‘/views’”

app.engine(ext, callback)

Register the given template engine callback as ext

By default will require() the engine based on the file extension. For example if you try to render a “foo.jade” file Express will invoke the following internally, and cache the require() on subsequent calls to increase performance.

app.engine('jade', require('jade').__express)

For engines that do not provide .__express out of the box - or if you wish to “map” a different extension to the template engine you may use this method. For example mapping the EJS template engine to “.html” files:

app.engine('html', require('ejs').renderFile)

In this case EJS provides a .renderFile() method with the same signature that Express expects: (path, options, callback), though note that it aliases this method as ejs.__express internally so if you’re using “.ejs” extensions you dont need to do anything.

Some template engines do not follow this convention, the consolidate.js library was created to map all of node’s popular template engines to follow this convention, thus allowing them to work seemlessly within Express.

var engines = require('consolidate')
app.engine('haml', engines.haml)
app.engine('html', engines.hogan)

app.param([name], callback)

Map logic to route parameters. For example when :user is present in a route path you may map user loading logic to automatically provide req.user to the route, or perform validations on the parameter input.

The following snippet illustrates how the callback is much like middleware, thus supporting async operations, however providing the additional value of the parameter, here named as id. An attempt to load the user is then performed, assigning req.user, otherwise passing an error to next(err).

app.param('user', function (req, res, next, id) {
  User.find(id, function (err, user) {
    if (err) {
      next(err)
    } else if (user) {
      req.user = user
      next()
    } else {
      next(new Error('failed to load user'))
    }
  })
})

Alternatively you may pass only a callback, in which case you have the opportunity to alter the app.param() API. For example the express-params defines the following callback which allows you to restrict parameters to a given regular expression.

This example is a bit more advanced, checking if the second argument is a regular expression, returning the callback which acts much like the “user” param example.

app.param(function (name, fn) {
  if (fn instanceof RegExp) {
    return function (req, res, next, val) {
      var captures
      if ((captures = fn.exec(String(val)))) {
        req.params[name] = captures
        next()
      } else {
        next('route')
      }
    }
  }
})

The method could now be used to effectively validate parameters, or also parse them to provide capture groups:

app.param('id', /^\d+$/)

app.get('/user/:id', function (req, res) {
  res.send('user ' + req.params.id)
})

app.param('range', /^(\w+)\.\.(\w+)?$/)

app.get('/range/:range', function (req, res) {
  var range = req.params.range
  res.send('from ' + range[1] + ' to ' + range[2])
})

app.VERB(path, [callback...], callback)

The app.VERB() methods provide the routing functionality in Express, where VERB is one of the HTTP verbs, such as app.post(). Multiple callbacks may be given, all are treated equally, and behave just like middleware, with the one exception that these callbacks may invoke next('route') to bypass the remaining route callback(s). This mechanism can be used to perform pre-conditions on a route then pass control to subsequent routes when there is no reason to proceed with the route matched.

The following snippet illustrates the most simple route definition possible. Express translates the path strings to regular expressions, used internally to match incoming requests. Query strings are not considered when peforming these matches, for example “GET /” would match the following route, as would “GET /?name=tobi”.

app.get('/', function (req, res) {
  res.send('hello world')
})

Regular expressions may also be used, and can be useful if you have very specific restraints, for example the following would match “GET /commits/71dbb9c” as well as “GET /commits/71dbb9c..4c084f9”.

app.get(/^\/commits\/(\w+)(?:\.\.(\w+))?$/, function (req, res) {
  var from = req.params[0]
  var to = req.params[1] || 'HEAD'
  res.send('commit range ' + from + '..' + to)
})

Several callbacks may also be passed, useful for re-using middleware that load resources, perform validations, etc.

app.get('/user/:id', user.load, function () {
  // ...
})

These callbacks may be passed within arrays as well, these arrays are simply flattened when passed:

var middleware = [loadForum, loadThread]

app.get('/forum/:fid/thread/:tid', middleware, function () {
  // ...
})

app.post('/forum/:fid/thread/:tid', middleware, function () {
  // ...
})

app.all(path, [callback...], callback)

This method functions just like the app.VERB() methods, however it matches all HTTP verbs.

This method is extremely useful for mapping “global” logic for specific path prefixes or arbitrary matches. For example if you placed the following route at the top of all other route definitions, it would require that all routes from that point on would require authentication, and automatically load a user. Keep in mind that these callbacks do not have to act as end points, loadUser can perform a task, then next() to continue matching subsequent routes.

app.all('*', requireAuthentication, loadUser)

Or the equivalent:

app.all('*', requireAuthentication)
app.all('*', loadUser)

Another great example of this is white-listed “global” functionality. Here the example is much like before, however only restricting paths prefixed with “/api”:

app.all('/api/*', requireAuthentication)

app.locals

Application local variables are provided to all templates rendered within the application. This is useful for providing helper functions to templates, as well as app-level data.

app.locals.title = 'My App'
app.locals.strftime = require('strftime')

The app.locals object is a JavaScript Function, which when invoked with an object will merge properties into itself, providing a simple way to expose existing objects as local variables.

app.locals({
  title: 'My App',
  phone: '1-250-858-9990',
  email: 'me@myapp.com'
})

console.log(app.locals.title)
// => 'My App'

console.log(app.locals.email)
// => 'me@myapp.com'

A consequence of the app.locals Object being ultimately a Javascript Function Object is that you must not reuse existing (native) named properties for your own variable names, such as name, apply, bind, call, arguments, length, constructor.

app.locals({ name: 'My App' })

console.log(app.locals.name)
// => return 'app.locals' in place of 'My App' (app.locals is a Function !)
// => if name's variable is used in a template, a ReferenceError will be returned.

The full list of native named properties can be found in many specifications. The JavaScript specification introduced original properties, some of which still recognized by modern engines, and the EcmaScript specification then built on it and normalized the set of properties, adding new ones and removing deprecated ones. Check out properties for Functions and Objects if interested.

By default Express exposes only a single app-level local variable, settings.

app.set('title', 'My App')
// use settings.title in a view

app.render(view, [options], callback)

Render a view with a callback responding with the rendered string. This is the app-level variant of res.render(), and otherwise behaves the same way.

app.render('email', function (err, html) {
  // ...
})

app.render('email', { name: 'Tobi' }, function (err, html) {
  // ...
})

app.routes

The app.routes object houses all of the routes defined mapped by the associated HTTP verb. This object may be used for introspection capabilities, for example Express uses this internally not only for routing but to provide default

OPTIONS

behaviour unless app.options() is used. Your application or framework may also remove routes by simply by removing them from this object.

The output of console.log(app.routes):

{ get:
   [ { path: '/',
       method: 'get',
       callbacks: [Object],
       keys: [],
       regexp: /^\/\/?$/i },
     { path: '/user/:id',
       method: 'get',
       callbacks: [Object],
       keys: [{ name: 'id', optional: false }],
       regexp: /^\/user\/(?:([^\/]+?))\/?$/i } ],
  delete:
   [ { path: '/user/:id',
       method: 'delete',
       callbacks: [Object],
       keys: [Object],
       regexp: /^\/user\/(?:([^\/]+?))\/?$/i } ] }

app.listen()

Bind and listen for connections on the given host and port, this method is identical to node’s http.Server#listen().

var express = require('express')
var app = express()
app.listen(3000)

The app returned by express() is in fact a JavaScript Function, designed to be passed to node’s http servers as a callback to handle requests. This allows you to provide both HTTP and HTTPS versions of your app with the same codebase easily, as the app does not inherit from these, it is simply a callback:

var express = require('express')
var https = require('https')
var http = require('http')
var app = express()

http.createServer(app).listen(80)
https.createServer(options, app).listen(443)

The app.listen() method is simply a convenience method defined as, if you wish to use HTTPS or provide both, use the technique above.

app.listen = function () {
  var server = http.createServer(this)
  return server.listen.apply(server, arguments)
}

Request

The req object is an enhanced version of Node’s own request object and supports all built-in fields and methods.

req.params

This property is an array containing properties mapped to the named route “parameters”. For example if you have the route /user/:name, then the “name” property is available to you as req.params.name. This object defaults to {}.

// GET /user/tj
console.dir(req.params.name)
// => 'tj'

When a regular expression is used for the route definition, capture groups are provided in the array using req.params[N], where N is the nth capture group. This rule is applied to unnamed wild-card matches with string routes such as /file/*:

// GET /file/javascripts/jquery.js
console.dir(req.params[0])
// => 'javascripts/jquery.js'

req.query

This property is an object containing the parsed query-string, defaulting to {}.

// GET /search?q=tobi+ferret
console.dir(req.query.q)
// => 'tobi ferret'

// GET /shoes?order=desc&shoe[color]=blue&shoe[type]=converse
console.dir(req.query.order)
// => 'desc'

console.dir(req.query.shoe.color)
// => 'blue'

console.dir(req.query.shoe.type)
// => 'converse'

req.body

This property is an object containing the parsed request body. This feature is provided by the bodyParser() middleware, though other body parsing middleware may follow this convention as well. This property defaults to {} when bodyParser() is used.

// POST user[name]=tobi&user[email]=tobi@learnboost.com
console.log(req.body.user.name)
// => "tobi"

console.log(req.body.user.email)
// => "tobi@learnboost.com"

// POST { "name": "tobi" }
console.log(req.body.name)
// => "tobi"

req.files

This property is an object of the files uploaded. This feature is provided by the bodyParser() middleware, though other body parsing middleware may follow this convention as well. This property defaults to {} when bodyParser() is used.

For example if a file field was named “image”, and a file was uploaded, req.files.image would contain the following File object:

{ size: 74643,
  path: '/tmp/8ef9c52abe857867fd0a4e9a819d1876',
  name: 'edge.png',
  type: 'image/png',
  hash: false,
  lastModifiedDate: Thu Aug 09 2012 20:07:51 GMT-0700 (PDT),
  _writeStream:
   { path: '/tmp/8ef9c52abe857867fd0a4e9a819d1876',
     fd: 13,
     writable: false,
     flags: 'w',
     encoding: 'binary',
     mode: 438,
     bytesWritten: 74643,
     busy: false,
     _queue: [],
     _open: [Function],
     drainable: true },
  length: [Getter],
  filename: [Getter],
  mime: [Getter] }

The bodyParser() middleware utilizes the node-formidable module internally, and accepts the same options. An example of this is the keepExtensions formidable option, defaulting to false which in this case gives you the filename “/tmp/8ef9c52abe857867fd0a4e9a819d1876” void of the “.png” extension. To enable this, and others you may pass them to bodyParser():

app.use(express.bodyParser({ keepExtensions: true, uploadDir: '/my/files' }))

req.param(name)

Return the value of param name when present.

// ?name=tobi
req.param('name')
// => "tobi"

// POST name=tobi
req.param('name')
// => "tobi"

// /user/tobi for /user/:name
req.param('name')
// => "tobi"

Lookup is performed in the following order:

• req.params
• req.body
• req.query

Direct access to req.body, req.params, and req.query should be favoured for clarity - unless you truly accept input from each object.

req.route

The currently matched Route containing several properties such as the route’s original path string, the regexp generated, and so on.

app.get('/user/:id?', function (req, res) {
  console.dir(req.route)
})

Example output from the previous snippet:

{ path: '/user/:id?',
  method: 'get',
  callbacks: [ [Function] ],
  keys: [ { name: 'id', optional: true } ],
  regexp: /^\/user(?:\/([^\/]+?))?\/?$/i,
  params: [ id: '12' ] }

req.cookies

This object requires the cookieParser() middleware for use. It contains cookies sent by the user-agent. If no cookies are sent, it defaults to {}.

// Cookie: name=tj
console.log(req.cookies.name)
// => "tj"

req.signedCookies

This object requires the cookieParser(secret) middleware for use. It contains signed cookies sent by the user-agent, unsigned and ready for use. Signed cookies reside in a different object to show developer intent; otherwise, a malicious attack could be placed on req.cookie values (which are easy to spoof). Note that signing a cookie does not make it “hidden” or encrypted; this simply prevents tampering (because the secret used to sign is private). If no signed cookies are sent, it defaults to {}.

// Cookie: user=tobi.CP7AWaXDfAKIRfH49dQzKJx7sKzzSoPq7/AcBBRVwlI3
console.dir(req.signedCookies.user)
// => 'tobi'

req.get(field)

Get the case-insensitive request header field. The “Referrer” and “Referer” fields are interchangeable.

req.get('Content-Type')
// => "text/plain"

req.get('content-type')
// => "text/plain"

req.get('Something')
// => undefined

p Aliased as req.header(field).

req.accepts(types)

Check if the given types are acceptable, returning the best match when true, otherwise undefined - in which case you should respond with 406 “Not Acceptable”.

The type value may be a single mime type string such as “application/json”, the extension name such as “json”, a comma-delimited list or an array. When a list or array is given the best match, if any is returned.

// Accept: text/html
req.accepts('html')
// => "html"

// Accept: text/*, application/json
req.accepts('html')
// => "html"
req.accepts('text/html')
// => "text/html"
req.accepts('json, text')
// => "json"
req.accepts('application/json')
// => "application/json"

// Accept: text/*, application/json
req.accepts('image/png')
req.accepts('png')
// => undefined

// Accept: text/*;q=.5, application/json
req.accepts(['html', 'json'])
req.accepts('html, json')
// => "json"

req.accepted

Return an array of Accepted media types ordered from highest quality to lowest.

[ { value: 'application/json',
    quality: 1,
    type: 'application',
    subtype: 'json' },
   { value: 'text/html',
     quality: 0.5,
     type: 'text',
     subtype: 'html' } ]

req.is(type)

Check if the incoming request contains the “Content-Type” header field, and it matches the give mime type.

// With Content-Type: text/html; charset=utf-8
req.is('html')
req.is('text/html')
req.is('text/*')
// => true

// When Content-Type is application/json
req.is('json')
req.is('application/json')
req.is('application/*')
// => true

req.is('html')
// => false

req.ip

Return the remote address, or when “trust proxy” is enabled - the upstream address.

console.dir(req.ip)
// => '127.0.0.1'

req.ips

When “trust proxy” is true, parse the “X-Forwarded-For” ip address list and return an array, otherwise an empty array is returned.

For example if the value were “client, proxy1, proxy2” you would receive the array ["client", "proxy1", "proxy2"] where “proxy2” is the furthest down-stream.

req.path

Returns the request URL pathname.

// example.com/users?sort=desc
console.dir(req.path)
// => '/users'

req.host

Returns the hostname from the “Host” header field (void of portno).

// Host: "example.com:3000"
console.dir(req.host)
// => 'example.com'

req.fresh

Check if the request is fresh - aka Last-Modified and/or the ETag still match, indicating that the resource is “fresh”.

console.dir(req.fresh)
// => true

req.stale

Check if the request is stale - aka Last-Modified and/or the ETag do not match, indicating that the resource is “stale”.

console.dir(req.stale)
// => true

req.xhr

Check if the request was issued with the “X-Requested-With” header field set to “XMLHttpRequest” (jQuery etc).

console.dir(req.xhr)
// => true

req.protocol

Return the protocol string “http” or “https” when requested with TLS. When the “trust proxy” setting is enabled the “X-Forwarded-Proto” header field will be trusted. If you’re running behind a reverse proxy that supplies https for you this may be enabled.

console.dir(req.protocol)
// => 'http'

req.secure

Check if a TLS connection is established. This is a short-hand for:

console.dir(req.protocol === 'https')
// => true

req.subdomains

Return subdomains as an array.

// Host: "tobi.ferrets.example.com"
console.dir(req.subdomains)
// => ['ferrets', 'tobi']

req.originalUrl

This property is much like req.url, however it retains the original request url, allowing you to rewrite req.url freely for internal routing purposes. For example the “mounting” feature of app.use() will rewrite req.url to strip the mount point.

// GET /search?q=something
console.log(req.originalUrl)
// => "/search?q=something"

req.acceptedLanguages

Return an array of Accepted languages ordered from highest quality to lowest.

Accept-Language: en;q=.5, en-us
// => ['en-us', 'en']

req.acceptedCharsets

Return an array of Accepted charsets ordered from highest quality to lowest.

Accept-Charset: iso-8859-5;q=.2, unicode-1-1;q=0.8
// => ['unicode-1-1', 'iso-8859-5']

req.acceptsCharset(charset)

Check if the given charset are acceptable.

req.acceptsLanguage(lang)

Check if the given lang are acceptable.

Response

The res object is an enhanced version of Node’s own response object and supports all built-in fields and methods.

res.status(code)

Chainable alias of node’s res.statusCode=.

res.status(404).sendfile('path/to/404.png')

res.set(field, [value])

Set header field to value, or pass an object to set multiple fields at once.

res.set('Content-Type', 'text/plain')

res.set({
  'Content-Type': 'text/plain',
  'Content-Length': '123',
  'ETag': '12345'
})

Aliased as res.header(field, [value]).

res.get(field)

Get the case-insensitive response header field.

res.get('Content-Type')
// => "text/plain"

res.cookie(name, value, [options])

Set cookie name to value, which may be a string or object converted to JSON. The path option defaults to “/”.

res.cookie('name', 'tobi', { domain: '.example.com', path: '/admin', secure: true })
res.cookie('rememberme', '1', { expires: new Date(Date.now() + 900000), httpOnly: true })

The maxAge option is a convenience option for setting “expires” relative to the current time in milliseconds. The following is equivalent to the previous example.

res.cookie('rememberme', '1', { maxAge: 900000, httpOnly: true })

An object may be passed which is then serialized as JSON, which is automatically parsed by the bodyParser() middleware.

res.cookie('cart', { items: [1, 2, 3] })
res.cookie('cart', { items: [1, 2, 3] }, { maxAge: 900000 })

Signed cookies are also supported through this method. Simply pass the signed option. When given res.cookie() will use the secret passed to express.cookieParser(secret) to sign the value.

res.cookie('name', 'tobi', { signed: true })

Later you may access this value through the req.signedCookie object.

res.clearCookie(name, [options])

Clear cookie name. The path option defaults to “/”.

res.cookie('name', 'tobi', { path: '/admin' })
res.clearCookie('name', { path: '/admin' })

res.redirect([status], url)

Redirect to the given url with optional status code defaulting to 302 “Found”.

res.redirect('/foo/bar')
res.redirect('http://example.com')
res.redirect(301, 'http://example.com')
res.redirect('../login')

Express supports a few forms of redirection, first being a fully qualified URI for redirecting to a different site:

res.redirect('http://google.com')

The second form is the pathname-relative redirect, for example if you were on http://example.com/admin/post/new, the following redirect to /admin would land you at http://example.com/admin:

res.redirect('/admin')

This next redirect is relative to the mount point of the application. For example if you have a blog application mounted at /blog, ideally it has no knowledge of where it was mounted, so where a redirect of /admin/post/new would simply give you http://example.com/admin/post/new, the following mount-relative redirect would give you http://example.com/blog/admin/post/new:

res.redirect('admin/post/new')

Pathname relative redirects are also possible. If you were on http://example.com/admin/post/new, the following redirect would land you at http//example.com/admin/post:

res.redirect('..')

The final special-case is a back redirect, redirecting back to the Referer (or Referrer), defaulting to / when missing.

res.redirect('back')

res.location

Set the location header.

res.location('/foo/bar')
res.location('foo/bar')
res.location('http://example.com')
res.location('../login')
res.location('back')

You can use the same kind of urls as in res.redirect().

For example, if your application is mounted at /blog, the following would set the location header to /blog/admin:

res.location('admin')

res.charset

Assign the charset. Defaults to “utf-8”.

res.charset = 'value'
res.send('<p>some html</p>')
// => Content-Type: text/html; charset=value

res.send([body|status], [body])

Send a response.

res.send(Buffer.from('whoop'))
res.send({ some: 'json' })
res.send('<p>some html</p>')
res.send(404, 'Sorry, we cannot find that!')
res.send(500, { error: 'something blew up' })
res.send(200)

This method performs a myriad of useful tasks for simple non-streaming responses such as automatically assigning the Content-Length unless previously defined and providing automatic HEAD and HTTP cache freshness support.

When a Buffer is given the Content-Type is set to “application/octet-stream” unless previously defined as shown below:

res.set('Content-Type', 'text/html')
res.send(Buffer.from('<p>some html</p>'))

When a String is given the Content-Type is set defaulted to “text/html”:

res.send('<p>some html</p>')

When an Array or Object is given Express will respond with the JSON representation:

res.send({ user: 'tobi' })
res.send([1, 2, 3])

Finally when a Number is given without any of the previously mentioned bodies, then a response body string is assigned for you. For example 200 will respond will the text “OK”, and 404 “Not Found” and so on.

res.send(200)
res.send(404)
res.send(500)

res.json([status|body], [body])

Send a JSON response. This method is identical to res.send() when an object or array is passed, however it may be used for explicit JSON conversion of non-objects (null, undefined, etc), though these are technically not valid JSON.

res.json(null)
res.json({ user: 'tobi' })
res.json(500, { error: 'message' })

res.jsonp([status|body], [body])

Send a JSON response with JSONP support. This method is identical to res.json() however opts-in to JSONP callback support.

res.jsonp(null)
// => null

res.jsonp({ user: 'tobi' })
// => { "user": "tobi" }

res.jsonp(500, { error: 'message' })
// => { "error": "message" }

By default the JSONP callback name is simply callback, however you may alter this with the jsonp callback name setting. The following are some examples of JSONP responses using the same code:

// ?callback=foo
res.jsonp({ user: 'tobi' })
// => foo({ "user": "tobi" })

app.set('jsonp callback name', 'cb')

// ?cb=foo
res.jsonp(500, { error: 'message' })
// => foo({ "error": "message" })

res.type(type)

Sets the Content-Type to the mime lookup of type, or when “/” is present the Content-Type is simply set to this literal value.

res.type('.html')
res.type('html')
res.type('json')
res.type('application/json')
res.type('png')

p Aliased as res.contentType(type).

res.format(object)

Performs content-negotiation on the request Accept header field when present. This method uses req.accepted, an array of acceptable types ordered by their quality values, otherwise the first callback is invoked. When no match is performed the server responds with 406 “Not Acceptable”, or invokes the default callback.

The Content-Type is set for you when a callback is selected, however you may alter this within the callback using res.set() or res.type() etcetera.

The following example would respond with { "message": "hey" } when the Accept header field is set to “application/json” or “/json”, however if “/*” is given then “hey” will be the response.

res.format({
  'text/plain': function () {
    res.send('hey')
  },

  'text/html': function () {
    res.send('<p>hey</p>')
  },

  'application/json': function () {
    res.send({ message: 'hey' })
  }
})

In addition to canonicalized MIME types you may also use extnames mapped to these types, providing a slightly less verbose implementation:

res.format({
  text: function () {
    res.send('hey')
  },

  html: function () {
    res.send('<p>hey</p>')
  },

  json: function () {
    res.send({ message: 'hey' })
  }
})

res.attachment([filename])

Sets the Content-Disposition header field to “attachment”. If a filename is given then the Content-Type will be automatically set based on the extname via res.type(), and the Content-Disposition’s “filename=” parameter will be set.

res.attachment()
// Content-Disposition: attachment

res.attachment('path/to/logo.png')
// Content-Disposition: attachment; filename="logo.png"
// Content-Type: image/png

res.sendfile(path, [options], [fn]])

Transfer the file at the given path.

Automatically defaults the Content-Type response header field based on the filename’s extension. The callback fn(err) is invoked when the transfer is complete or when an error occurs.

Options:

• maxAge in milliseconds defaulting to 0
• root root directory for relative filenames

This method provides fine-grained support for file serving as illustrated in the following example:

app.get('/user/:uid/photos/:file', function (req, res) {
  var uid = req.params.uid
  var file = req.params.file

  req.user.mayViewFilesFrom(uid, function (yes) {
    if (yes) {
      res.sendfile('/uploads/' + uid + '/' + file)
    } else {
      res.send(403, 'Sorry! you cant see that.')
    }
  })
})

res.download(path, [filename], [fn])

Transfer the file at path as an “attachment”, typically browsers will prompt the user for download. The Content-Disposition “filename=” parameter, aka the one that will appear in the brower dialog is set to path by default, however you may provide an override filename.

When an error has ocurred or transfer is complete the optional callback fn is invoked. This method uses res.sendfile() to transfer the file.

res.download('/report-12345.pdf')

res.download('/report-12345.pdf', 'report.pdf')

res.download('/report-12345.pdf', 'report.pdf', function (err) {
  if (err) {
    // handle error, keep in mind the response may be partially-sent
    // so check res.headerSent
  } else {
    // decrement a download credit etc
  }
})

res.links(links)

Join the given links to populate the “Link” response header field.

res.links({
  next: 'http://api.example.com/users?page=2',
  last: 'http://api.example.com/users?page=5'
})

p yields:

Link: <http://api.example.com/users?page=2> rel="next",
      <http://api.example.com/users?page=5> rel="last"

res.locals

Response local variables are scoped to the request, thus only available to the view(s) rendered during that request / response cycle, if any. Otherwise this API is identical to app.locals.

This object is useful for exposing request-level information such as the request pathname, authenticated user, user settings etcetera.

app.use(function (req, res, next) {
  res.locals.user = req.user
  res.locals.authenticated = !req.user.anonymous
  next()
})

res.render(view, [locals], callback)

Render a view with a callback responding with the rendered string. When an error occurs next(err) is invoked internally. When a callback is provided both the possible error and rendered string are passed, and no automated response is performed.

res.render('index', function (err, html) {
  // ...
})

res.render('user', { name: 'Tobi' }, function (err, html) {
  // ...
})

Middleware

basicAuth()

Basic Authentication middleware, populating req.user with the username.

Simple username and password:

app.use(express.basicAuth('username', 'password'))

Callback verification:

app.use(express.basicAuth(function (user, pass) {
  return user === 'tj' && pass === 'wahoo'
}))

Async callback verification, accepting fn(err, user), in this case req.user will be the user object passed.

app.use(express.basicAuth(function (user, pass, fn) {
  User.authenticate({ user: user, pass: pass }, fn)
}))

bodyParser()

Request body parsing middleware supporting JSON, urlencoded, and multipart requests. This middleware is simply a wrapper for the json(), urlencoded(), and multipart() middleware.

app.use(express.bodyParser())

// is equivalent to:
app.use(express.json())
app.use(express.urlencoded())
app.use(express.multipart())

For security sake, it’s better to disable file upload if your application doesn’t need it. To do this, use only the needed middleware, i.e. don’t use the bodyParser and multipart() middleware:

app.use(express.json())
app.use(express.urlencoded())

If your application needs file upload you should set up a strategy for dealing with those files.

compress()

Compress response data with gzip / deflate. This middleware should be placed “high” within the stack to ensure all responses may be compressed.

app.use(express.logger())
app.use(express.compress())
app.use(express.methodOverride())
app.use(express.bodyParser())

cookieParser()

Parses the Cookie header field and populates req.cookies with an object keyed by the cookie names. Optionally you may enabled signed cookie support by passing a secret string.

app.use(express.cookieParser())
app.use(express.cookieParser('some secret'))

cookieSession()

Provides cookie-based sessions, and populates req.session. This middleware takes the following options:

• key cookie name defaulting to connect.sess
• secret prevents cookie tampering
• cookie session cookie settings, defaulting to { path: '/', httpOnly: true, maxAge: null }
• proxy trust the reverse proxy when setting secure cookies (via “x-forwarded-proto”)

app.use(express.cookieSession())

To clear a cookie simply assign the session to null before responding:

req.session = null

csrf()

CSRF protection middleware.

By default this middleware generates a token named “_csrf” which should be added to requests which mutate state, within a hidden form field, query-string etc. This token is validated against req.csrfToken().

The default value function checks req.body generated by the bodyParser() middleware, req.query generated by query(), and the “X-CSRF-Token” header field.

This middleware requires session support, thus should be added somewhere below session().

directory()

Directory serving middleware, serves the given path. This middleware may be paired with static() to serve files, providing a full-featured file browser.

app.use(express.directory('public'))
app.use(express.static('public'))

This middleware accepts the following options:

• hidden display hidden (dot) files. Defaults to false.
• icons display icons. Defaults to false.
• filter Apply this filter function to files. Defaults to false.