4.x API
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()
Methods
express.json([options])
This middleware is available in Express v4.16.0 onwards.
This is a built-in middleware function in Express. It parses incoming requests with JSON payloads and is based on body-parser.
Returns middleware that only parses JSON and only looks at requests where
the Content-Type
header matches the type
option. This parser accepts any
Unicode encoding of the body and supports automatic inflation of gzip
and
deflate
encodings.
A new body
object containing the parsed data is populated on the request
object after the middleware (i.e. req.body
), or an empty object ({}
) if
there was no body to parse, the Content-Type
was not matched, or an error
occurred.
As req.body
’s shape is based on user-controlled input, all properties and
values in this object are untrusted and should be validated before trusting.
For example, req.body.foo.toString()
may fail in multiple ways, for example
foo
may not be there or may not be a string, and toString
may not be a
function and instead a string or other user-input.
The following table describes the properties of the optional options
object.
| Property | Description | Type | Default |
|---|---|---|---|
inflate |
Enables or disables handling deflated (compressed) bodies; when disabled, deflated bodies are rejected. | Boolean | true |
limit |
Controls the maximum request body size. If this is a number, then the value specifies the number of bytes; if it is a string, the value is passed to the bytes library for parsing. | Mixed | "100kb" |
reviver |
The reviver option is passed directly to JSON.parse as the second argument. You can find more information on this argument in the MDN documentation about JSON.parse. |
Function | null |
strict |
Enables or disables only accepting arrays and objects; when disabled will accept anything JSON.parse accepts. |
Boolean | true |
type |
This is used to determine what media type the middleware will parse. This option can be a string, array of strings, or a function. If not a function, type option is passed directly to the type-is library and this can be an extension name (like json ), a mime type (like application/json ), or a mime type with a wildcard (like */* or */json ). If a function, the type option is called as fn(req) and the request is parsed if it returns a truthy value. |
Mixed | "application/json" |
verify |
This option, if supplied, is called as verify(req, res, buf, encoding) , where buf is a Buffer of the raw request body and encoding is the encoding of the request. The parsing can be aborted by throwing an error. |
Function | undefined |
express.raw([options])
This middleware is available in Express v4.17.0 onwards.
This is a built-in middleware function in Express. It parses incoming request
payloads into a Buffer
and is based on
body-parser.
Returns middleware that parses all bodies as a Buffer
and only looks at requests
where the Content-Type
header matches the type
option. This parser accepts
any Unicode encoding of the body and supports automatic inflation of gzip
and
deflate
encodings.
A new body
Buffer
containing the parsed data is populated on the request
object after the middleware (i.e. req.body
), or an empty object ({}
) if
there was no body to parse, the Content-Type
was not matched, or an error
occurred.
As req.body
’s shape is based on user-controlled input, all properties and
values in this object are untrusted and should be validated before trusting.
For example, req.body.toString()
may fail in multiple ways, for example
stacking multiple parsers req.body
may be from a different parser. Testing
that req.body
is a Buffer
before calling buffer methods is recommended.
The following table describes the properties of the optional options
object.
| Property | Description | Type | Default |
|---|---|---|---|
inflate |
Enables or disables handling deflated (compressed) bodies; when disabled, deflated bodies are rejected. | Boolean | true |
limit |
Controls the maximum request body size. If this is a number, then the value specifies the number of bytes; if it is a string, the value is passed to the bytes library for parsing. | Mixed | "100kb" |
type |
This is used to determine what media type the middleware will parse. This option can be a string, array of strings, or a function. If not a function, type option is passed directly to the type-is library and this can be an extension name (like bin ), a mime type (like application/octet-stream ), or a mime type with a wildcard (like */* or application/* ). If a function, the type option is called as fn(req) and the request is parsed if it returns a truthy value. |
Mixed | "application/octet-stream" |
verify |
This option, if supplied, is called as verify(req, res, buf, encoding) , where buf is a Buffer of the raw request body and encoding is the encoding of the request. The parsing can be aborted by throwing an error. |
Function | undefined |
express.Router([options])
Creates a new router object.
var router = express.Router([options])
The optional options
parameter specifies the behavior of the router.
| Property | Description | Default | Availability |
|---|---|---|---|
caseSensitive |
Enable case sensitivity. | Disabled by default, treating "/Foo" and "/foo" as the same. | |
mergeParams |
Preserve the req.params values from the parent router. If the parent and the child have conflicting param names, the child’s value take precedence. |
false |
4.5.0+ |
strict |
Enable strict routing. | Disabled by default, "/foo" and "/foo/" are treated the same by the router. |
You can add middleware and HTTP method routes (such as get
, put
, post
, and
so on) to router
just like an application.
For more information, see Router.
express.static(root, [options])
This is a built-in middleware function in Express. It serves static files and is based on serve-static.
NOTE: For best results, use a reverse proxy cache to improve performance of serving static assets.
The root
argument specifies the root directory from which to serve static assets.
The function determines the file to serve by combining req.url
with the provided root
directory.
When a file is not found, instead of sending a 404 response, it instead calls next()
to move on to the next middleware, allowing for stacking and fall-backs.
The following table describes the properties of the options
object.
See also the example below.
| Property | Description | Type | Default |
|---|---|---|---|
dotfiles |
Determines how dotfiles (files or directories that begin with a dot ".") are treated. See dotfiles below. |
String | "ignore" |
etag |
Enable or disable etag generation NOTE: express.static always sends weak ETags. |
Boolean | true |
extensions |
Sets file extension fallbacks: If a file is not found, search for files with the specified extensions and serve the first one found. Example: ['html', 'htm'] . |
Mixed | false |
fallthrough |
Let client errors fall-through as unhandled requests, otherwise forward a client error. See fallthrough below. |
Boolean | true |
immutable |
Enable or disable the immutable directive in the Cache-Control response header. If enabled, the maxAge option should also be specified to enable caching. The immutable directive will prevent supported clients from making conditional requests during the life of the maxAge option to check if the file has changed. |
Boolean | false |
index |
Sends the specified directory index file. Set to false to disable directory indexing. |
Mixed | "index.html" |
lastModified |
Set the Last-Modified header to the last modified date of the file on the OS. |
Boolean | true |
maxAge |
Set the max-age property of the Cache-Control header in milliseconds or a string in ms format. | Number | 0 |
redirect |
Redirect to trailing "/" when the pathname is a directory. | Boolean | true |
setHeaders |
Function for setting HTTP headers to serve with the file. See setHeaders below. |
Function |
For more information, see Serving static files in Express. and Using middleware - Built-in middleware.
dotfiles
Possible values for this option are:
- "allow" - No special treatment for dotfiles.
- "deny" - Deny a request for a dotfile, respond with
403
, then callnext()
. - "ignore" - Act as if the dotfile does not exist, respond with
404
, then callnext()
.
NOTE: With the default value, it will not ignore files in a directory that begins with a dot.
fallthrough
When this option is true
, client errors such as a bad request or a request to a non-existent
file will cause this middleware to simply call next()
to invoke the next middleware in the stack.
When false, these errors (even 404s), will invoke next(err)
.
Set this option to true
so you can map multiple physical directories
to the same web address or for routes to fill in non-existent files.
Use false
if you have mounted this middleware at a path designed
to be strictly a single file system directory, which allows for short-circuiting 404s
for less overhead. This middleware will also reply to all methods.
setHeaders
For this option, specify a function to set custom response headers. Alterations to the headers must occur synchronously.
The signature of the function is:
fn(res, path, stat)
Arguments:
res
, the response object.path
, the file path that is being sent.stat
, thestat
object of the file that is being sent.
Example of express.static
Here is an example of using the express.static
middleware function with an elaborate options object:
var options = {
dotfiles: 'ignore',
etag: false,
extensions: ['htm', 'html'],
index: false,
maxAge: '1d',
redirect: false,
setHeaders: function (res, path, stat) {
res.set('x-timestamp', Date.now())
}
}
app.use(express.static('public', options))
express.text([options])
This middleware is available in Express v4.17.0 onwards.
This is a built-in middleware function in Express. It parses incoming request payloads into a string and is based on body-parser.
Returns middleware that parses all bodies as a string and only looks at requests
where the Content-Type
header matches the type
option. This parser accepts
any Unicode encoding of the body and supports automatic inflation of gzip
and
deflate
encodings.
A new body
string containing the parsed data is populated on the request
object after the middleware (i.e. req.body
), or an empty object ({}
) if
there was no body to parse, the Content-Type
was not matched, or an error
occurred.
As req.body
’s shape is based on user-controlled input, all properties and
values in this object are untrusted and should be validated before trusting.
For example, req.body.trim()
may fail in multiple ways, for example
stacking multiple parsers req.body
may be from a different parser. Testing
that req.body
is a string before calling string methods is recommended.
The following table describes the properties of the optional options
object.
| Property | Description | Type | Default |
|---|---|---|---|
defaultCharset |
Specify the default character set for the text content if the charset is not specified in the Content-Type header of the request. |
String | "utf-8" |
inflate |
Enables or disables handling deflated (compressed) bodies; when disabled, deflated bodies are rejected. | Boolean | true |
limit |
Controls the maximum request body size. If this is a number, then the value specifies the number of bytes; if it is a string, the value is passed to the bytes library for parsing. | Mixed | "100kb" |
type |
This is used to determine what media type the middleware will parse. This option can be a string, array of strings, or a function. If not a function, type option is passed directly to the type-is library and this can be an extension name (like txt ), a mime type (like text/plain ), or a mime type with a wildcard (like */* or text/* ). If a function, the type option is called as fn(req) and the request is parsed if it returns a truthy value. |
Mixed | "text/plain" |
verify |
This option, if supplied, is called as verify(req, res, buf, encoding) , where buf is a Buffer of the raw request body and encoding is the encoding of the request. The parsing can be aborted by throwing an error. |
Function | undefined |
express.urlencoded([options])
This middleware is available in Express v4.16.0 onwards.
This is a built-in middleware function in Express. It parses incoming requests with urlencoded payloads and is based on body-parser.
Returns middleware that only parses urlencoded bodies and only looks at
requests where the Content-Type
header matches the type
option. This
parser accepts only UTF-8 encoding of the body and supports automatic
inflation of gzip
and deflate
encodings.
A new body
object containing the parsed data is populated on the request
object after the middleware (i.e. req.body
), or an empty object ({}
) if
there was no body to parse, the Content-Type
was not matched, or an error
occurred. This object will contain key-value pairs, where the value can be
a string or array (when extended
is false
), or any type (when extended
is true
).
As req.body
’s shape is based on user-controlled input, all properties and
values in this object are untrusted and should be validated before trusting.
For example, req.body.foo.toString()
may fail in multiple ways, for example
foo
may not be there or may not be a string, and toString
may not be a
function and instead a string or other user-input.
The following table describes the properties of the optional options
object.
| Property | Description | Type | Default |
|---|---|---|---|
extended |
This option allows to choose between parsing the URL-encoded data with the querystring library (when false ) or the qs library (when true ). The "extended" syntax allows for rich objects and arrays to be encoded into the URL-encoded format, allowing for a JSON-like experience with URL-encoded. For more information, please see the qs library. |
Boolean | true |
inflate |
Enables or disables handling deflated (compressed) bodies; when disabled, deflated bodies are rejected. | Boolean | true |
limit |
Controls the maximum request body size. If this is a number, then the value specifies the number of bytes; if it is a string, the value is passed to the bytes library for parsing. | Mixed | "100kb" |
parameterLimit |
This option controls the maximum number of parameters that are allowed in the URL-encoded data. If a request contains more parameters than this value, an error will be raised. | Number | 1000 |
type |
This is used to determine what media type the middleware will parse. This option can be a string, array of strings, or a function. If not a function, type option is passed directly to the type-is library and this can be an extension name (like urlencoded ), a mime type (like application/x-www-form-urlencoded ), or a mime type with a wildcard (like */x-www-form-urlencoded ). If a function, the type option is called as fn(req) and the request is parsed if it returns a truthy value. |
Mixed | "application/x-www-form-urlencoded" |
verify |
This option, if supplied, is called as verify(req, res, buf, encoding) , where buf is a Buffer of the raw request body and encoding is the encoding of the request. The parsing can be aborted by throwing an error. |
Function | undefined |
Application
The app
object conventionally denotes the Express application.
Create it by calling the top-level express()
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)
The app
object has methods for
- Routing HTTP requests; see for example, app.METHOD and app.param.
- Configuring middleware; see app.route.
- Rendering HTML views; see app.render.
- Registering a template engine; see app.engine.
It also has settings (properties) that affect how the application behaves; for more information, see Application settings.
The Express application object can be referred from the request object and the response object as req.app
, and res.app
, respectively.
Properties
app.locals
The app.locals
object has properties that are local variables within the application.
console.dir(app.locals.title)
// => 'My App'
console.dir(app.locals.email)
// =><EMAIL_ADDRESS>Once set, the value of app.locals
properties persist throughout the life of the application,
in contrast with res.locals properties that
are valid only for the lifetime of the request.
You can access local variables in templates rendered within the application.
This is useful for providing helper functions to templates, as well as application-level data.
Local variables are available in middleware via req.app.locals
(see req.app)
app.locals.title = 'My App'
app.locals.strftime = require('strftime')
app.locals.email =<EMAIL_ADDRESS>app.mountpath
The app.mountpath
property contains one or more path patterns on which a sub-app was mounted.
A sub-app is an instance of express
that may be used for handling the request to a route.
var express = require('express')
var app = express() // the main app
var admin = express() // the sub app
admin.get('/', function (req, res) {
console.log(admin.mountpath) // /admin
res.send('Admin Homepage')
})
app.use('/admin', admin) // mount the sub app
It is similar to the baseUrl property of the req
object, except req.baseUrl
returns the matched URL path, instead of the matched patterns.
If a sub-app is mounted on multiple path patterns, app.mountpath
returns the list of
patterns it is mounted on, as shown in the following example.
var admin = express()
admin.get('/', function (req, res) {
console.dir(admin.mountpath) // [ '/adm*n', '/manager' ]
res.send('Admin Homepage')
})
var secret = express()
secret.get('/', function (req, res) {
console.log(secret.mountpath) // /secr*t
res.send('Admin Secret')
})
admin.use('/secr*t', secret) // load the 'secret' router on '/secr*t', on the 'admin' sub app
app.use(['/adm*n', '/manager'], admin) // load the 'admin' router on '/adm*n' and '/manager', on the parent app
Events
app.on('mount', callback(parent))
The mount
event is fired on a sub-app, when it is mounted on a parent app. The parent app is passed to the callback function.
NOTE
Sub-apps will:
- Not inherit the value of settings that have a default value. You must set the value in the sub-app.
- Inherit the value of settings with no default value.
For details, see Application settings.
var admin = express()
admin.on('mount', function (parent) {
console.log('Admin Mounted')
console.log(parent) // refers to the parent app
})
admin.get('/', function (req, res) {
res.send('Admin Homepage')
})
app.use('/admin', admin)
Methods
app.all(path, callback [, callback ...])
This method is like the standard app.METHOD() methods, except it matches all HTTP verbs.
Arguments
| Argument | Description | Default |
|---|---|---|
path |
The path for which the middleware function is invoked; can be any of:
|
'/' (root path) |
callback |
Callback functions; can be:
You can provide multiple callback functions that behave just like middleware, except
that these callbacks can invoke Since router and app implement the middleware interface, you can use them as you would any other middleware function. For examples, see Middleware callback function examples. |
None |
Examples
The following callback is executed for requests to /secret
whether using
GET, POST, PUT, DELETE, or any other HTTP request method:
app.all('/secret', function (req, res, next) {
console.log('Accessing the secret section ...')
next() // pass control to the next handler
})
The app.all()
method is useful for mapping "global" logic for specific path prefixes or arbitrary matches. For example, if you put the following at the top of all other
route definitions, it requires that all routes from that point on
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 call next()
to continue matching subsequent
routes.
app.all('*', requireAuthentication, loadUser)
Or the equivalent:
app.all('*', requireAuthentication)
app.all('*', loadUser)
Another example is white-listed "global" functionality. The example is similar to the ones above, but it only restricts paths that start with "/api":
app.all('/api/*', requireAuthentication)
app.delete(path, callback [, callback ...])
Routes HTTP DELETE requests to the specified path with the specified callback functions. For more information, see the routing guide.
Arguments
| Argument | Description | Default |
|---|---|---|
path |
The path for which the middleware function is invoked; can be any of:
|
'/' (root path) |
callback |
Callback functions; can be:
You can provide multiple callback functions that behave just like middleware, except
that these callbacks can invoke Since router and app implement the middleware interface, you can use them as you would any other middleware function. For examples, see Middleware callback function examples. |
None |
Example
app.delete('/', function (req, res) {
res.send('DELETE request to homepage')
})
app.disable(name)
Sets the Boolean setting name
to false
, where name
is one of the properties from the app settings table.
Calling app.set('foo', false)
for a Boolean property is the same as calling app.disable('foo')
.
For example:
app.disable('trust proxy')
app.get('trust proxy')
// => false
app.disabled(name)
Returns true
if the Boolean setting name
is disabled (false
), where name
is one of the properties from
the app settings table.
app.disabled('trust proxy')
// => true
app.enable('trust proxy')
app.disabled('trust proxy')
// => false
app.enable(name)
Sets the Boolean setting name
to true
, where name
is one of the properties from the app settings table.
Calling app.set('foo', true)
for a Boolean property is the same as calling app.enable('foo')
.
app.enable('trust proxy')
app.get('trust proxy')
// => true
app.enabled(name)
Returns true
if the setting name
is enabled (true
), where name
is one of the
properties from the app settings table.
app.enabled('trust proxy')
// => false
app.enable('trust proxy')
app.enabled('trust proxy')
// => true
app.engine(ext, callback)
Registers the given template engine callback
as ext
.
By default, Express will require()
the engine based on the file extension.
For example, if you try to render a "foo.pug" file, Express invokes the
following internally, and caches the require()
on subsequent calls to increase
performance.
app.engine('pug', require('pug').__express)
Use this method for engines that do not provide .__express
out of the box,
or if you wish to "map" a different extension to the template engine.
For example, to map 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 don’t need to do anything.
Some template engines do not follow this convention. The consolidate.js library maps Node template engines to follow this convention, so they work seamlessly with Express.
var engines = require('consolidate')
app.engine('haml', engines.haml)
app.engine('html', engines.hogan)
app.get(name)
Returns the value of name
app setting, where name
is one of the strings in the
app settings table. For example:
app.get('title')
// => undefined
app.set('title', 'My Site')
app.get('title')
// => "My Site"
app.get(path, callback [, callback ...])
Routes HTTP GET requests to the specified path with the specified callback functions.
Arguments
| Argument | Description | Default |
|---|---|---|
path |
The path for which the middleware function is invoked; can be any of:
|
'/' (root path) |
callback |
Callback functions; can be:
You can provide multiple callback functions that behave just like middleware, except
that these callbacks can invoke Since router and app implement the middleware interface, you can use them as you would any other middleware function. For examples, see Middleware callback function examples. |
None |
For more information, see the routing guide.
Example
app.get('/', function (req, res) {
res.send('GET request to homepage')
})
app.listen(path, [callback])
Starts a UNIX socket and listens for connections on the given path. This method is identical to Node’s http.Server.listen().
var express = require('express')
var app = express()
app.listen('/tmp/sock')
app.listen([port[, host[, backlog]]][, callback])
Binds and listens for connections on the specified host and port. This method is identical to Node’s http.Server.listen().
If port is omitted or is 0, the operating system will assign an arbitrary unused port, which is useful for cases like automated tasks (tests, etc.).
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 makes it easy to provide both HTTP and HTTPS versions of
your app with the same code base, 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 returns an http.Server object and (for HTTP) is a convenience method for the following:
app.listen = function () {
var server = http.createServer(this)
return server.listen.apply(server, arguments)
}
NOTE: All the forms of Node’s http.Server.listen() method are in fact actually supported.
app.METHOD(path, callback [, callback ...])
Routes an HTTP request, where METHOD is the HTTP method of the request, such as GET,
PUT, POST, and so on, in lowercase. Thus, the actual methods are app.get()
,
app.post()
, app.put()
, and so on. See Routing methods below for the complete list.
Arguments
| Argument | Description | Default |
|---|---|---|
path |
The path for which the middleware function is invoked; can be any of:
|
'/' (root path) |
callback |
Callback functions; can be:
You can provide multiple callback functions that behave just like middleware, except
that these callbacks can invoke Since router and app implement the middleware interface, you can use them as you would any other middleware function. For examples, see Middleware callback function examples. |
None |
Routing methods
Express supports the following routing methods corresponding to the HTTP methods of the same names:
|
|
|
The API documentation has explicit entries only for the most popular HTTP methods app.get()
,
app.post()
, app.put()
, and app.delete()
.
However, the other methods listed above work in exactly the same way.
To route methods that translate to invalid JavaScript variable names, use the bracket notation. For example, app['m-search']('/', function ...
.
The app.get()
function is automatically called for the HTTP HEAD
method in addition to the GET
method if app.head()
was not called for the path before app.get()
.
The method, app.all()
, is not derived from any HTTP method and loads middleware at
the specified path for all HTTP request methods.
For more information, see app.all.
For more information on routing, see the routing guide.
app.param([name], callback)
Add callback triggers to route parameters, where name
is the name of the parameter or an array of them, and callback
is the callback function. The parameters of the callback function are the request object, the response object, the next middleware, the value of the parameter and the name of the parameter, in that order.
If name
is an array, the callback
trigger is registered for each parameter declared in it, in the order in which they are declared. Furthermore, for each declared parameter except the last one, a call to next
inside the callback will call the callback for the next declared parameter. For the last parameter, a call to next
will call the next middleware in place for the route currently being processed, just like it would if name
were just a string.
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.
app.param('user', function (req, res, next, id) {
// try to get the user details from the User model and attach it to the request object
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'))
}
})
})
Param callback functions are local to the router on which they are defined. They are not inherited by mounted apps or routers. Hence, param callbacks defined on app
will be triggered only by route parameters defined on app
routes.
All param callbacks will be called before any handler of any route in which the param occurs, and they will each be called only once in a request-response cycle, even if the parameter is matched in multiple routes, as shown in the following examples.
app.param('id', function (req, res, next, id) {
console.log('CALLED ONLY ONCE')
next()
})
app.get('/user/:id', function (req, res, next) {
console.log('although this matches')
next()
})
app.get('/user/:id', function (req, res) {
console.log('and this matches too')
res.end()
})
On GET /user/42
, the following is printed:
CALLED ONLY ONCE
although this matches
and this matches too
app.param(['id', 'page'], function (req, res, next, value) {
console.log('CALLED ONLY ONCE with', value)
next()
})
app.get('/user/:id/:page', function (req, res, next) {
console.log('although this matches')
next()
})
app.get('/user/:id/:page', function (req, res) {
console.log('and this matches too')
res.end()
})
On GET /user/42/3
, the following is printed:
CALLED ONLY ONCE with 42
CALLED ONLY ONCE with 3
although this matches
and this matches too
The following section describes app.param(callback)
, which is deprecated as of v4.11.0.
The behavior of the app.param(name, callback)
method can be altered entirely by passing only a function to app.param()
. This function is a custom implementation of how app.param(name, callback)
should behave - it accepts two parameters and must return a middleware.
The first parameter of this function is the name of the URL parameter that should be captured, the second parameter can be any JavaScript object which might be used for returning the middleware implementation.
The middleware returned by the function decides the behavior of what happens when a URL parameter is captured.
In this example, the app.param(name, callback)
signature is modified to app.param(name, accessId)
. Instead of accepting a name and a callback, app.param()
will now accept a name and a number.
var express = require('express')
var app = express()
// customizing the behavior of app.param()
app.param(function (param, option) {
return function (req, res, next, val) {
if (val === option) {
next()
} else {
next('route')
}
}
})
// using the customized app.param()
app.param('id', 1337)
// route to trigger the capture
app.get('/user/:id', function (req, res) {
res.send('OK')
})
app.listen(3000, function () {
console.log('Ready')
})
In this example, the app.param(name, callback)
signature remains the same, but instead of a middleware callback, a custom data type checking function has been defined to validate the data type of the user id.
app.param(function (param, validator) {
return function (req, res, next, val) {
if (validator(val)) {
next()
} else {
next('route')
}
}
})
app.param('id', function (candidate) {
return !isNaN(parseFloat(candidate)) && isFinite(candidate)
})
The ‘.
’ character can’t be used to capture a character in your capturing regexp. For example you can’t use '/user-.+/'
to capture 'users-gami'
, use [\\s\\S]
or [\\w\\W]
instead (as in '/user-[\\s\\S]+/'
.
Examples:
//captures '1-a_6' but not '543-azser-sder'
router.get('/[0-9]+-[[\\w]]*', function);
//captures '1-a_6' and '543-az(ser"-sder' but not '5-a s'
router.get('/[0-9]+-[[\\S]]*', function);
//captures all (equivalent to '.*')
router.get('[[\\s\\S]]*', function);
app.path()
Returns the canonical path of the app, a string.
var app = express()
var blog = express()
var blogAdmin = express()
app.use('/blog', blog)
blog.use('/admin', blogAdmin)
console.dir(app.path()) // ''
console.dir(blog.path()) // '/blog'
console.dir(blogAdmin.path()) // '/blog/admin'
The behavior of this method can become very complicated in complex cases of mounted apps: it is usually better to use req.baseUrl to get the canonical path of the app.
app.post(path, callback [, callback ...])
Routes HTTP POST requests to the specified path with the specified callback functions. For more information, see the routing guide.
Arguments
| Argument | Description | Default |
|---|---|---|
path |
The path for which the middleware function is invoked; can be any of:
|
'/' (root path) |
callback |
Callback functions; can be:
You can provide multiple callback functions that behave just like middleware, except
that these callbacks can invoke Since router and app implement the middleware interface, you can use them as you would any other middleware function. For examples, see Middleware callback function examples. |
None |
Example
app.post('/', function (req, res) {
res.send('POST request to homepage')
})
app.put(path, callback [, callback ...])
Routes HTTP PUT requests to the specified path with the specified callback functions.
Arguments
| Argument | Description | Default |
|---|---|---|
path |
The path for which the middleware function is invoked; can be any of:
|
'/' (root path) |
callback |
Callback functions; can be:
You can provide multiple callback functions that behave just like middleware, except
that these callbacks can invoke Since router and app implement the middleware interface, you can use them as you would any other middleware function. For examples, see Middleware callback function examples. |
None |
Example
app.put('/', function (req, res) {
res.send('PUT request to homepage')
})
app.render(view, [locals], callback)
Returns the rendered HTML of a view via the callback
function. It accepts an optional parameter
that is an object containing local variables for the view. It is like res.render(),
except it cannot send the rendered view to the client on its own.
Think of app.render()
as a utility function for generating rendered view strings.
Internally res.render()
uses app.render()
to render views.
The local variable cache
is reserved for enabling view cache. Set it to true
, if you want to
cache view during development; view caching is enabled in production by default.
app.render('email', function (err, html) {
// ...
})
app.render('email', { name: 'Tobi' }, function (err, html) {
// ...
})
app.route(path)
Returns an instance of a single route, which you can then use to handle HTTP verbs with optional middleware.
Use app.route()
to avoid duplicate route names (and thus typo errors).
var app = express()
app.route('/events')
.all(function (req, res, next) {
// runs for all HTTP verbs first
// think of it as route specific middleware!
})
.get(function (req, res, next) {
res.json({})
})
.post(function (req, res, next) {
// maybe add a new event...
})
app.set(name, value)
Assigns setting name
to value
. You may store any value that you want,
but certain names can be used to configure the behavior of the server. These
special names are listed in the app settings table.
Calling app.set('foo', true)
for a Boolean property is the same as calling
app.enable('foo')
. Similarly, calling app.set('foo', false)
for a Boolean
property is the same as calling app.disable('foo')
.
Retrieve the value of a setting with app.get()
.
app.set('title', 'My Site')
app.get('title') // "My Site"
Application Settings
The following table lists application settings.
Note that sub-apps will:
- Not inherit the value of settings that have a default value. You must set the value in the sub-app.
- Inherit the value of settings with no default value; these are explicitly noted in the table below.
Exceptions: Sub-apps will inherit the value of trust proxy
even though it has a default value (for backward-compatibility);
Sub-apps will not inherit the value of view cache
in production (when NODE_ENV
is "production").
| Property | Type | Description | Default |
|---|---|---|---|
|
|
Boolean | Enable case sensitivity. When enabled, "/Foo" and "/foo" are different routes. When disabled, "/Foo" and "/foo" are treated the same. NOTE: Sub-apps will inherit the value of this setting. |
N/A (undefined) |
|
|
String | Environment mode. Be sure to set to "production" in a production environment; see Production best practices: performance and reliability. |
|
|
|
Varied |
Set the ETag response header. For possible values, see the |
|
|
|
String | Specifies the default JSONP callback name. |
"callback" |
|
|
Boolean |
Enable escaping JSON responses from the NOTE: Sub-apps will inherit the value of this setting. |
N/A (undefined) |
|
|
Varied | The 'replacer' argument used by `JSON.stringify`.
NOTE: Sub-apps will inherit the value of this setting. |
N/A (undefined) |
|
|
Varied | The 'space' argument used by `JSON.stringify`.
This is typically set to the number of spaces to use to indent prettified JSON.
NOTE: Sub-apps will inherit the value of this setting. |
N/A (undefined) |
|
|
Varied |
Disable query parsing by setting the value to The simple query parser is based on Node’s native query parser, querystring. The extended query parser is based on qs. A custom query string parsing function will receive the complete query string, and must return an object of query keys and their values. |
"extended" |
|
|
Boolean | Enable strict routing. When enabled, the router treats "/foo" and "/foo/" as different. Otherwise, the router treats "/foo" and "/foo/" as the same. NOTE: Sub-apps will inherit the value of this setting. |
N/A (undefined) |
|
|
Number | The number of dot-separated parts of the host to remove to access subdomain. | 2 |
|
|
Varied |
Indicates the app is behind a front-facing proxy, and to use the When enabled, Express attempts to determine the IP address of the client connected through the front-facing proxy, or series of proxies. The `req.ips` property, then contains an array of IP addresses the client is connected through. To enable it, use the values described in the trust proxy options table. The `trust proxy` setting is implemented using the proxy-addr package. For more information, see its documentation. NOTE: Sub-apps will inherit the value of this setting, even though it has a default value. |
|
|
|
String or Array | A directory or an array of directories for the application's views. If an array, the views are looked up in the order they occur in the array. |
|
|
|
Boolean | Enables view template compilation caching. NOTE: Sub-apps will not inherit the value of this setting in production (when `NODE_ENV` is "production"). |
|
|
|
String | The default engine extension to use when omitted.
NOTE: Sub-apps will inherit the value of this setting. |
N/A (undefined) |
|
|
Boolean | Enables the "X-Powered-By: Express" HTTP header. |
|
Options for `trust proxy` setting
Read Express behind proxies for more information.
| Type | Value |
|---|---|
| Boolean |
If If |
| String String containing comma-separated values Array of strings |
An IP address, subnet, or an array of IP addresses, and subnets to trust. Pre-configured subnet names are:
Set IP addresses in any of the following ways: Specify a single subnet:
Specify a subnet and an address:
Specify multiple subnets as CSV:
Specify multiple subnets as an array:
When specified, the IP addresses or the subnets are excluded from the address determination process, and the untrusted IP address nearest to the application server is determined as the client’s IP address. |
| Number |
Trust the nth hop from the front-facing proxy server as the client. |
| Function |
Custom trust implementation. Use this only if you know what you are doing.
|
Options for `etag` setting
NOTE: These settings apply only to dynamic files, not static files. The express.static middleware ignores these settings.
The ETag functionality is implemented using the etag package. For more information, see its documentation.
| Type | Value |
|---|---|
| Boolean |
|
| String |
If "strong", enables strong ETag. If "weak", enables weak ETag. |
| Function |
Custom ETag function implementation. Use this only if you know what you are doing.
|
app.use([path,] callback [, callback...])
Mounts the specified middleware function or functions
at the specified path:
the middleware function is executed when the base of the requested path matches path
.
Arguments
| Argument | Description | Default |
|---|---|---|
path |
The path for which the middleware function is invoked; can be any of:
|
'/' (root path) |
callback |
Callback functions; can be:
You can provide multiple callback functions that behave just like middleware, except
that these callbacks can invoke Since router and app implement the middleware interface, you can use them as you would any other middleware function. For examples, see Middleware callback function examples. |
None |
Description
A route will match any path that follows its path immediately with a "/
".
For example: app.use('/apple', ...)
will match "/apple", "/apple/images",
"/apple/images/news", and so on.
Since path
defaults to "/", middleware mounted without a path will be executed for every request to the app.
For example, this middleware function will be executed for every request to the app:
app.use(function (req, res, next) {
console.log('Time: %d', Date.now())
next()
})
NOTE
Sub-apps will:
- Not inherit the value of settings that have a default value. You must set the value in the sub-app.
- Inherit the value of settings with no default value.
For details, see Application settings.
Middleware functions are executed sequentially, therefore the order of middleware inclusion is important.
// this middleware will not allow the request to go beyond it
app.use(function (req, res, next) {
res.send('Hello World')
})
// requests will never reach this route
app.get('/', function (req, res) {
res.send('Welcome')
})
Error-handling middleware
Error-handling middleware always takes four arguments. You must provide four arguments to identify it as an error-handling middleware function. Even if you don’t need to use the next
object, you must specify it to maintain the signature. Otherwise, the next
object will be interpreted as regular middleware and will fail to handle errors. For details about error-handling middleware, see: Error handling.
Define error-handling middleware functions in the same way as other middleware functions, except with four arguments instead of three, specifically with the signature (err, req, res, next)
):
app.use(function (err, req, res, next) {
console.error(err.stack)
res.status(500).send('Something broke!')
})
Path examples
The following table provides some simple examples of valid path
values for
mounting middleware.
| Type | Example |
|---|---|
| Path |
This will match paths starting with `/abcd`:
|
| Path Pattern |
This will match paths starting with `/abcd` and `/abd`:
This will match paths starting with `/abcd`, `/abbcd`, `/abbbbbcd`, and so on:
This will match paths starting with `/abcd`, `/abxcd`, `/abFOOcd`, `/abbArcd`, and so on:
This will match paths starting with `/ad` and `/abcd`:
|
| Regular Expression |
This will match paths starting with `/abc` and `/xyz`:
|
| Array |
This will match paths starting with `/abcd`, `/xyza`, `/lmn`, and `/pqr`:
|
Middleware callback function examples
The following table provides some simple examples of middleware functions that
can be used as the callback
argument to app.use()
, app.METHOD()
, and app.all()
.
Even though the examples are for app.use()
, they are also valid for app.use()
, app.METHOD()
, and app.all()
.
| Usage | Example |
|---|---|
| Single Middleware | You can define and mount a middleware function locally.
A router is valid middleware.
An Express app is valid middleware.
|
| Series of Middleware |
You can specify more than one middleware function at the same mount path.
|
| Array |
Use an array to group middleware logically.
If you pass an array of middleware as the first or only middleware parameters,
then you must specify the mount path.
|
| Combination |
You can combine all the above ways of mounting middleware.
|
Following are some examples of using the express.static middleware in an Express app.
Serve static content for the app from the "public" directory in the application directory:
// GET /style.css etc
app.use(express.static(path.join(__dirname, 'public')))
Mount the middleware at "/static" to serve static content only when their request path is prefixed with "/static":
// GET /static/style.css etc.
app.use('/static', express.static(path.join(__dirname, 'public')))
Disable logging for static content requests by loading the logger middleware after the static middleware:
app.use(express.static(path.join(__dirname, 'public')))
app.use(logger())
Serve static files from multiple directories, but give 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')))
Request
The req
object represents the HTTP request and has properties for the
request query string, parameters, body, HTTP headers, and so on. In this documentation and by convention,
the object is always referred to as req
(and the HTTP response is res
) but its actual name is determined
by the parameters to the callback function in which you’re working.
For example:
app.get('/user/:id', function (req, res) {
res.send('user ' + req.params.id)
})
But you could just as well have:
app.get('/user/:id', function (request, response) {
response.send('user ' + request.params.id)
})
The req
object is an enhanced version of Node’s own request object
and supports all built-in fields and methods.
Properties
In Express 4, req.files
is no longer available on the req
object by default. To access uploaded files
on the req.files
object, use multipart-handling middleware like busboy, multer,
formidable,
multiparty,
connect-multiparty,
or pez.
req.app
This property holds a reference to the instance of the Express application that is using the middleware.
If you follow the pattern in which you create a module that just exports a middleware function
and require()
it in your main file, then the middleware can access the Express instance via req.app
For example:
// index.js
app.get('/viewdirectory', require('./mymiddleware.js'))
// mymiddleware.js
module.exports = function (req, res) {
res.send('The views directory is ' + req.app.get('views'))
}
req.baseUrl
The URL path on which a router instance was mounted.
The req.baseUrl
property is similar to the mountpath property of the app
object,
except app.mountpath
returns the matched path pattern(s).
For example:
var greet = express.Router()
greet.get('/jp', function (req, res) {
console.log(req.baseUrl) // /greet
res.send('Konichiwa!')
})
app.use('/greet', greet) // load the router on '/greet'
Even if you use a path pattern or a set of path patterns to load the router,
the baseUrl
property returns the matched string, not the pattern(s). In the
following example, the greet
router is loaded on two path patterns.
app.use(['/gre+t', '/hel{2}o'], greet) // load the router on '/gre+t' and '/hel{2}o'
When a request is made to /greet/jp
, req.baseUrl
is "/greet". When a request is
made to /hello/jp
, req.baseUrl
is "/hello".
req.body
Contains key-value pairs of data submitted in the request body.
By default, it is undefined
, and is populated when you use body-parsing middleware such
as express.json()
or express.urlencoded()
.
The following example shows how to use body-parsing middleware to populate req.body
.
var express = require('express')
var app = express()
app.use(express.json()) // for parsing application/json
app.use(express.urlencoded({ extended: true })) // for parsing application/x-www-form-urlencoded
app.post('/profile', function (req, res, next) {
console.log(req.body)
res.json(req.body)
})
req.cookies
When using cookie-parser middleware, this property is an object that
contains cookies sent by the request. If the request contains no cookies, it defaults to {}
.
// Cookie: name=tj
console.dir(req.cookies.name)
// => 'tj'
If the cookie has been signed, you have to use req.signedCookies.
For more information, issues, or concerns, see cookie-parser.
req.fresh
When the response is still "fresh" in the client’s cache true
is returned, otherwise false
is returned to indicate that the client cache is now stale and the full response should be sent.
When a client sends the Cache-Control: no-cache
request header to indicate an end-to-end reload request, this module will return false
to make handling these requests transparent.
Further details for how cache validation works can be found in the HTTP/1.1 Caching Specification.
console.dir(req.fresh)
// => true
req.hostname
Contains the hostname derived from the Host
HTTP header.
When the trust proxy
setting
does not evaluate to false
, this property will instead get the value
from the X-Forwarded-Host
header field. This header can be set by
the client or by the proxy.
If there is more than one X-Forwarded-Host
header in the request, the
value of the first header is used. This includes a single header with
comma-separated values, in which the first value is used.
Prior to Express v4.17.0, the X-Forwarded-Host
could not contain multiple
values or be present more than once.
// Host: "example.com:3000"
console.dir(req.hostname)
// => 'example.com'
req.ip
Contains the remote IP address of the request.
When the trust proxy
setting does not evaluate to false
,
the value of this property is derived from the left-most entry in the
X-Forwarded-For
header. This header can be set by the client or by the proxy.
console.dir(req.ip)
// => '<IP_ADDRESS>'
req.ips
When the trust proxy
setting does not evaluate to false
,
this property contains an array of IP addresses
specified in the X-Forwarded-For
request header. Otherwise, it contains an
empty array. This header can be set by the client or by the proxy.
For example, if X-Forwarded-For
is client, proxy1, proxy2
, req.ips
would be
["client", "proxy1", "proxy2"]
, where proxy2
is the furthest downstream.
req.method
Contains a string corresponding to the HTTP method of the request:
GET
, POST
, PUT
, and so on.
req.originalUrl
req.url
is not a native Express property, it is inherited from Node’s http module.
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.dir(req.originalUrl)
// => '/search?q=something'
In a middleware function, req.originalUrl
is a combination of req.baseUrl
and req.path
, as shown in the following example.
app.use('/admin', function (req, res, next) { // GET 'http://www.example.com/admin/new'
console.dir(req.originalUrl) // '/admin/new'
console.dir(req.baseUrl) // '/admin'
console.dir(req.path) // '/new'
next()
})
req.params
This property is an object containing properties mapped to the named route "parameters". For example, if you have the route /user/:name
, then the "name" property is available as req.params.name
. This object defaults to {}
.
// GET /user/tj
console.dir(req.params.name)
// => 'tj'
When you use a regular expression 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'
If you need to make changes to a key in req.params
, use the app.param handler. Changes are applicable only to parameters already defined in the route path.
Any changes made to the req.params
object in a middleware or route handler will be reset.
NOTE: Express automatically decodes the values in req.params
(using decodeURIComponent
).
req.path
Contains the path part of the request URL.
// example.com/users?sort=desc
console.dir(req.path)
// => '/users'
When called from a middleware, the mount point is not included in req.path
. See app.use() for more details.
req.protocol
Contains the request protocol string: either http
or (for TLS requests) https
.
When the trust proxy
setting does not evaluate to false
,
this property will use the value of the X-Forwarded-Proto
header field if present.
This header can be set by the client or by the proxy.
console.dir(req.protocol)
// => 'http'
req.query
This property is an object containing a property for each query string parameter in the route.
When query parser is set to disabled, it is an empty object {}
, otherwise it is the result of the configured query parser.
As req.query
’s shape is based on user-controlled input, all properties and values in this object are untrusted and should be validated before trusting. For example, req.query.foo.toString()
may fail in multiple ways, for example foo
may not be there or may not be a string, and toString
may not be a function and instead a string or other user-input.
 For example:
app.get('/user/:id?', function userIdHandler (req, res) {
console.log(req.route)
res.send('GET')
})
Example output from the previous snippet:
{ path: '/user/:id?',
stack:
[ { handle: [Function: userIdHandler],
name: 'userIdHandler',
params: undefined,
path: undefined,
keys: [],
regexp: /^\/?$/i,
method: 'get' } ],
methods: { get: true } }
req.secure
A Boolean property that is true if a TLS connection is established. Equivalent to:
console.dir(req.protocol === 'https')
// => true
req.signedCookies
When using cookie-parser middleware, this property
contains signed cookies sent by the request, 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; but simply prevents tampering (because the secret used to sign is private).
If no signed cookies are sent, the property defaults to {}
.
// Cookie: user=tobi.CP7AWaXDfAKIRfH49dQzKJx7sKzzSoPq7/AcBBRVwlI3
console.dir(req.signedCookies.user)
// => 'tobi'
For more information, issues, or concerns, see cookie-parser.
req.stale
Indicates whether the request is "stale," and is the opposite of req.fresh
.
For more information, see req.fresh.
console.dir(req.stale)
// => true
req.subdomains
An array of subdomains in the domain name of the request.
// Host: "tobi.ferrets.example.com"
console.dir(req.subdomains)
// => ['ferrets', 'tobi']
The application property subdomain offset
, which defaults to 2, is used for determining the
beginning of the subdomain segments. To change this behavior, change its value
using app.set.
req.xhr
A Boolean property that is true
if the request’s X-Requested-With
header field is
"XMLHttpRequest", indicating that the request was issued by a client library such as jQuery.
console.dir(req.xhr)
// => true
Methods
req.accepts(types)
Checks if the specified content types are acceptable, based on the request’s Accept
HTTP header field.
The method returns the best match, or if none of the specified content types is acceptable, returns
false
(in which case, the application should respond with 406 "Not Acceptable"
).
The type
value may be a single MIME type string (such as "application/json"),
an extension name such as "json", a comma-delimited list, or an array. For a
list or array, the method returns the best match (if any).
// 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')
// => false
// Accept: text/*;q=.5, application/json
req.accepts(['html', 'json'])
// => "json"
For more information, or if you have issues or concerns, see accepts.
req.acceptsCharsets(charset [, ...])
Returns the first accepted charset of the specified character sets,
based on the request’s Accept-Charset
HTTP header field.
If none of the specified charsets is accepted, returns false
.
For more information, or if you have issues or concerns, see accepts.
req.acceptsEncodings(encoding [, ...])
Returns the first accepted encoding of the specified encodings,
based on the request’s Accept-Encoding
HTTP header field.
If none of the specified encodings is accepted, returns false
.
For more information, or if you have issues or concerns, see accepts.
req.acceptsLanguages(lang [, ...])
Returns the first accepted language of the specified languages,
based on the request’s Accept-Language
HTTP header field.
If none of the specified languages is accepted, returns false
.
For more information, or if you have issues or concerns, see accepts.
req.get(field)
Returns the specified HTTP request header field (case-insensitive match).
The Referrer
and Referer
fields are interchangeable.
req.get('Content-Type')
// => "text/plain"
req.get('content-type')
// => "text/plain"
req.get('Something')
// => undefined
Aliased as req.header(field)
.
req.is(type)
Returns the matching content type if the incoming request’s "Content-Type" HTTP header field
matches the MIME type specified by the type
parameter. If the request has no body, returns null
.
Returns false
otherwise.
// With Content-Type: text/html; charset=utf-8
req.is('html')
// => 'html'
req.is('text/html')
// => 'text/html'
req.is('text/*')
// => 'text/*'
// When Content-Type is application/json
req.is('json')
// => 'json'
req.is('application/json')
// => 'application/json'
req.is('application/*')
// => 'application/*'
req.is('html')
// => false
For more information, or if you have issues or concerns, see type-is.
req.param(name [, defaultValue])
Deprecated. Use either req.params
, req.body
or req.query
, as applicable.
Returns 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
Optionally, you can specify defaultValue
to set a default value if the parameter is not found in any of the request objects.
Direct access to req.body
, req.params
, and req.query
should be favoured for clarity - unless you truly accept input from each object.
Body-parsing middleware must be loaded for req.param()
to work predictably. Refer req.body for details.
req.range(size[, options])
Range
header parser.
The size
parameter is the maximum size of the resource.
The options
parameter is an object that can have the following properties.
| Property | Type | Description |
|---|---|---|
combine |
Boolean | Specify if overlapping & adjacent ranges should be combined, defaults to false . When true , ranges will be combined and returned as if they were specified that way in the header. |
An array of ranges will be returned or negative numbers indicating an error parsing.
-2
signals a malformed header string-1
signals an unsatisfiable range
// parse header from request
var range = req.range(1000)
// the type of the range
if (range.type === 'bytes') {
// the ranges
range.forEach(function (r) {
// do something with r.start and r.end
})
}
Response
The res
object represents the HTTP response that an Express app sends when it gets an HTTP request.
In this documentation and by convention,
the object is always referred to as res
(and the HTTP request is req
) but its actual name is determined
by the parameters to the callback function in which you’re working.
For example:
app.get('/user/:id', function (req, res) {
res.send('user ' + req.params.id)
})
But you could just as well have:
app.get('/user/:id', function (request, response) {
response.send('user ' + request.params.id)
})
The res
object is an enhanced version of Node’s own response object
and supports all built-in fields and methods.
Properties
res.app
This property holds a reference to the instance of the Express application that is using the middleware.
res.app
is identical to the req.app property in the request object.
res.headersSent
Boolean property that indicates if the app sent HTTP headers for the response.
app.get('/', function (req, res) {
console.dir(res.headersSent) // false
res.send('OK')
console.dir(res.headersSent) // true
})
res.locals
An object that contains response local variables scoped to the request, and therefore available only to the view(s) rendered during that request / response cycle (if any). Otherwise, this property is identical to app.locals.
This property is useful for exposing request-level information such as the request path name, authenticated user, user settings, and so on.
app.use(function (req, res, next) {
res.locals.user = req.user
res.locals.authenticated = !req.user.anonymous
next()
})
Methods
res.append(field [, value])
res.append()
is supported by Express v4.11.0+
Appends the specified value
to the HTTP response header field
. If the header is not already set,
it creates the header with the specified value. The value
parameter can be a string or an array.
Note: calling res.set()
after res.append()
will reset the previously-set header value.
res.append('Link', ['<http://localhost/>', '<http://localhost:3000/>'])
res.append('Set-Cookie', 'foo=bar; Path=/; HttpOnly')
res.append('Warning', '199 Miscellaneous warning')
res.attachment([filename])
Sets the HTTP response Content-Disposition
header field to "attachment". If a filename
is given,
then it sets the Content-Type based on the extension name via res.type()
,
and sets the Content-Disposition
"filename=" parameter.
res.attachment()
// Content-Disposition: attachment
res.attachment('path/to/logo.png')
// Content-Disposition: attachment; filename="logo.png"
// Content-Type: image/png
res.cookie(name, value [, options])
Sets cookie name
to value
. The value
parameter may be a string or object converted to JSON.
The options
parameter is an object that can have the following properties.
| Property | Type | Description |
|---|---|---|
domain |
String | Domain name for the cookie. Defaults to the domain name of the app. |
encode |
Function | A synchronous function used for cookie value encoding. Defaults to encodeURIComponent . |
expires |
Date | Expiry date of the cookie in GMT. If not specified or set to 0, creates a session cookie. |
httpOnly |
Boolean | Flags the cookie to be accessible only by the web server. |
maxAge |
Number | Convenient option for setting the expiry time relative to the current time in milliseconds. |
path |
String | Path for the cookie. Defaults to "/". |
secure |
Boolean | Marks the cookie to be used with HTTPS only. |
signed |
Boolean | Indicates if the cookie should be signed. |
sameSite |
Boolean or String | Value of the "SameSite" Set-Cookie attribute. More information at https://tools.ietf.org/html/draft-ietf-httpbis-cookie-same-site-00#section-4.1.1. |
All res.cookie()
does is set the HTTP Set-Cookie
header with the options provided.
Any option not specified defaults to the value stated in RFC 6265.
For example:
res.cookie('name', 'tobi', { domain: '.example.com', path: '/admin', secure: true })
res.cookie('rememberme', '1', { expires: new Date(Date.now() + 900000), httpOnly: true })
You can set multiple cookies in a single response by calling res.cookie
multiple times, for example:
res
.status(201)
.cookie('access_token', 'Bearer ' + token, {
expires: new Date(Date.now() + 8 * 3600000) // cookie will be removed after 8 hours
})
.cookie('test', 'test')
.redirect(301, '/admin')
The encode
option allows you to choose the function used for cookie value encoding.
Does not support asynchronous functions.
Example use case: You need to set a domain-wide cookie for another site in your organization. This other site (not under your administrative control) does not use URI-encoded cookie values.
// Default encoding
res.cookie('some_cross_domain_cookie', 'http://mysubdomain.example.com', { domain: 'example.com' })
// Result: 'some_cross_domain_cookie=http%3A%2F%2Fmysubdomain.example.com; Domain=example.com; Path=/'
// Custom encoding
res.cookie('some_cross_domain_cookie', 'http://mysubdomain.example.com', { domain: 'example.com', encode: String })
// Result: 'some_cross_domain_cookie=http://mysubdomain.example.com; Domain=example.com; Path=/;'
The maxAge
option is a convenience option for setting "expires" relative to the current time in milliseconds.
The following is equivalent to the second example above.
res.cookie('rememberme', '1', { maxAge: 900000, httpOnly: true })
You can pass an object as the value
parameter; it is then serialized as JSON and parsed by bodyParser()
middleware.
res.cookie('cart', { items: [1, 2, 3] })
res.cookie('cart', { items: [1, 2, 3] }, { maxAge: 900000 })
When using cookie-parser middleware, this method also
supports signed cookies. Simply include the signed
option set to true
.
Then res.cookie()
will use the secret passed to 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])
Clears the cookie specified by name
. For details about the options
object, see res.cookie().
Web browsers and other compliant clients will only clear the cookie if the given
options
is identical to those given to res.cookie(), excluding
expires
and maxAge
.
res.cookie('name', 'tobi', { path: '/admin' })
res.clearCookie('name', { path: '/admin' })
res.download(path [, filename] [, options] [, fn])
The optional options
argument is supported by Express v4.16.0 onwards.
Transfers the file at path
as an "attachment". Typically, browsers will prompt the user for download.
By default, the Content-Disposition
header "filename=" parameter is path
(this typically appears in the browser dialog).
Override this default with the filename
parameter.
When an error occurs or transfer is complete, the method calls the optional callback function fn
.
This method uses res.sendFile() to transfer the file.
The optional options
argument passes through to the underlying res.sendFile()
call, and takes the exact same parameters.
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, but keep in mind the response may be partially-sent
// so check res.headersSent
} else {
// decrement a download credit, etc.
}
})
res.end([data] [, encoding])
Ends the response process. This method actually comes from Node core, specifically the response.end() method of http.ServerResponse.
Use to quickly end the response without any data. If you need to respond with data, instead use methods such as res.send() and res.json().
res.end()
res.status(404).end()
res.format(object)
Performs content-negotiation on the Accept
HTTP header on the request object, when present.
It uses req.accepts() to select a handler for the request, based on the acceptable
types ordered by their quality values. If the header is not specified, the first callback is invoked.
When no match is found, the server responds with 406 "Not Acceptable", or invokes the default
callback.
The Content-Type
response header is set when a callback is selected. However, you may alter
this within the callback using methods such as res.set()
or res.type()
.
The following example would respond with { "message": "hey" }
when the Accept
header field is set
to "application/json" or "*/json" (however if it is "*/*", then the response will be "hey").
res.format({
'text/plain': function () {
res.send('hey')
},
'text/html': function () {
res.send('<p>hey</p>')
},
'application/json': function () {
res.send({ message: 'hey' })
},
default: function () {
// log the request and respond with 406
res.status(406).send('Not Acceptable')
}
})
In addition to canonicalized MIME types, you may also use extension names mapped to these types for 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.get(field)
Returns the HTTP response header specified by field
.
The match is case-insensitive.
res.get('Content-Type')
// => "text/plain"
res.json([body])
Sends a JSON response. This method sends a response (with the correct content-type) that is the parameter converted to a JSON string using JSON.stringify().
The parameter can be any JSON type, including object, array, string, Boolean, number, or null, and you can also use it to convert other values to JSON.
res.json(null)
res.json({ user: 'tobi' })
res.status(500).json({ error: 'message' })
res.jsonp([body])
Sends a JSON response with JSONP support. This method is identical to res.json()
,
except that it opts-in to JSONP callback support.
res.jsonp(null)
// => callback(null)
res.jsonp({ user: 'tobi' })
// => callback({ "user": "tobi" })
res.status(500).jsonp({ error: 'message' })
// => callback({ "error": "message" })
By default, the JSONP callback name is simply callback
. Override 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.status(500).jsonp({ error: 'message' })
// => foo({ "error": "message" })
res.links(links)
Joins the links
provided as properties of the parameter to populate the response’s
Link
HTTP header field.
For example, the following call:
res.links({
next: 'http://api.example.com/users?page=2',
last: 'http://api.example.com/users?page=5'
})
Yields the following results:
Link: <http://api.example.com/users?page=2>; rel="next",
<http://api.example.com/users?page=5>; rel="last"
res.location(path)
Sets the response Location
HTTP header to the specified path
parameter.
res.location('/foo/bar')
res.location('http://example.com')
res.location('back')
A path
value of "back" has a special meaning, it refers to the URL specified in the Referer
header of the request. If the Referer
header was not specified, it refers to "/".
After encoding the URL, if not encoded already, Express passes the specified URL to the browser in the Location
header,
without any validation.
Browsers take the responsibility of deriving the intended URL from the current URL
or the referring URL, and the URL specified in the Location
header; and redirect the user accordingly.
res.redirect([status,] path)
Redirects to the URL derived from the specified path
, with specified status
, a positive integer
that corresponds to an HTTP status code .
If not specified, status
defaults to "302 "Found".
res.redirect('/foo/bar')
res.redirect('http://example.com')
res.redirect(301, 'http://example.com')
res.redirect('../login')
Redirects can be a fully-qualified URL for redirecting to a different site:
res.redirect('http://google.com')
Redirects can be relative to the root of the host name. For example, if the
application is on http://example.com/admin/post/new
, the following
would redirect to the URL http://example.com/admin
:
res.redirect('/admin')
Redirects can be relative to the current URL. For example,
from http://example.com/blog/admin/
(notice the trailing slash), the following
would redirect to the URL http://example.com/blog/admin/post/new
.
res.redirect('post/new')
Redirecting to post/new
from http://example.com/blog/admin
(no trailing slash),
will redirect to http://example.com/blog/post/new
.
If you found the above behavior confusing, think of path segments as directories (with trailing slashes) and files, it will start to make sense.
Path-relative redirects are also possible. If you were on
http://example.com/admin/post/new
, the following would redirect to
http://example.com/admin/post
:
res.redirect('..')
A back
redirection redirects the request back to the referer,
defaulting to /
when the referer is missing.
res.redirect('back')
res.render(view [, locals] [, callback])
Renders a view
and sends the rendered HTML string to the client.
Optional parameters:
locals
, an object whose properties define local variables for the view.callback
, a callback function. If provided, the method returns both the possible error and rendered string, but does not perform an automated response. When an error occurs, the method invokesnext(err)
internally.
The view
argument is a string that is the file path of the view file to render. This can be an absolute path, or a path relative to the views
setting. If the path does not contain a file extension, then the view engine
setting determines the file extension. If the path does contain a file extension, then Express will load the module for the specified template engine (via require()
) and render it using the loaded module’s __express
function.
For more information, see Using template engines with Express.
NOTE: The view
argument performs file system operations like reading a file from disk and evaluating Node.js modules, and as so for security reasons should not contain input from the end-user.
The local variable cache
enables view caching. Set it to true
,
to cache the view during development; view caching is enabled in production by default.
// send the rendered view to the client
res.render('index')
// if a callback is specified, the rendered HTML string has to be sent explicitly
res.render('index', function (err, html) {
res.send(html)
})
// pass a local variable to the view
res.render('user', { name: 'Tobi' }, function (err, html) {
// ...
})
res.send([body])
Sends the HTTP response.
The body
parameter can be a Buffer
object, a String
, an object, Boolean
, or an Array
.
For example:
res.send(Buffer.from('whoop'))
res.send({ some: 'json' })
res.send('<p>some html</p>')
res.status(404).send('Sorry, we cannot find that!')
res.status(500).send({ error: 'something blew up' })
This method performs many useful tasks for simple non-streaming responses:
For example, it automatically assigns the Content-Length
HTTP response header field
(unless previously defined) and provides automatic HEAD and HTTP cache freshness support.
When the parameter is a Buffer
object, the method sets the Content-Type
response header field 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 the parameter is a String
, the method sets the Content-Type
to "text/html":
res.send('<p>some html</p>')
When the parameter is an Array
or Object
, Express responds with the JSON representation:
res.send({ user: 'tobi' })
res.send([1, 2, 3])
res.sendFile(path [, options] [, fn])
res.sendFile()
is supported by Express v4.8.0 onwards.
Transfers the file at the given path
. Sets the Content-Type
response HTTP header field
based on the filename’s extension. Unless the root
option is set in
the options object, path
must be an absolute path to the file.
This API provides access to data on the running file system. Ensure that either (a) the way in
which the path
argument was constructed into an absolute path is secure if it contains user
input or (b) set the root
option to the absolute path of a directory to contain access within.
When the root
option is provided, the path
argument is allowed to be a relative path,
including containing ..
. Express will validate that the relative path provided as path
will
resolve within the given root
option.
The following table provides details on the options
parameter.
| Property | Description | Default | Availability |
|---|---|---|---|
maxAge |
Sets the max-age property of the Cache-Control header in milliseconds or a string in ms format |
0 | |
root |
Root directory for relative filenames. | ||
lastModified |
Sets the Last-Modified header to the last modified date of the file on the OS. Set false to disable it. |
Enabled | 4.9.0+ |
headers |
Object containing HTTP headers to serve with the file. | ||
dotfiles |
Option for serving dotfiles. Possible values are "allow", "deny", "ignore". | "ignore" | |
acceptRanges |
Enable or disable accepting ranged requests. | true |
4.14+ |
cacheControl |
Enable or disable setting Cache-Control response header. |
true |
4.14+ |
immutable |
Enable or disable the immutable directive in the Cache-Control response header. If enabled, the maxAge option should also be specified to enable caching. The immutable directive will prevent supported clients from making conditional requests during the life of the maxAge option to check if the file has changed. |
false |
4.16+ |
The method invokes the callback function fn(err)
when the transfer is complete
or when an error occurs. If the callback function is specified and an error occurs,
the callback function must explicitly handle the response process either by
ending the request-response cycle, or by passing control to the next route.
Here is an example of using res.sendFile
with all its arguments.
app.get('/file/:name', function (req, res, next) {
var options = {
root: path.join(__dirname, 'public'),
dotfiles: 'deny',
headers: {
'x-timestamp': Date.now(),
'x-sent': true
}
}
var fileName = req.params.name
res.sendFile(fileName, options, function (err) {
if (err) {
next(err)
} else {
console.log('Sent:', fileName)
}
})
})
The following example illustrates using
res.sendFile
to provide fine-grained support for serving files:
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.status(403).send("Sorry! You can't see that.")
}
})
})
For more information, or if you have issues or concerns, see send.
res.sendStatus(statusCode)
Sets the response HTTP status code to statusCode
and send its string representation as the response body.
res.sendStatus(200) // equivalent to res.status(200).send('OK')
res.sendStatus(403) // equivalent to res.status(403).send('Forbidden')
res.sendStatus(404) // equivalent to res.status(404).send('Not Found')
res.sendStatus(500) // equivalent to res.status(500).send('Internal Server Error')
If an unsupported status code is specified, the HTTP status is still set to statusCode
and the string version of the code is sent as the response body.
Some versions of Node.js will throw when res.statusCode
is set to an
invalid HTTP status code (outside of the range 100
to 599
). Consult
the HTTP server documentation for the Node.js version being used.
res.sendStatus(9999) // equivalent to res.status(9999).send('9999')
res.set(field [, value])
Sets the response’s HTTP header field
to value
.
To set multiple fields at once, pass an object as the parameter.
res.set('Content-Type', 'text/plain')
res.set({
'Content-Type': 'text/plain',
'Content-Length': '123',
ETag: '12345'
})
Aliased as res.header(field [, value])
.
res.status(code)
Sets the HTTP status for the response. It is a chainable alias of Node’s response.statusCode.
res.status(403).end()
res.status(400).send('Bad Request')
res.status(404).sendFile('/absolute/path/to/404.png')
res.type(type)
Sets the Content-Type
HTTP header to the MIME type as determined by
mime.lookup() for the specified type
.
If type
contains the "/" character, then it sets the Content-Type
to type
.
res.type('.html')
// => 'text/html'
res.type('html')
// => 'text/html'
res.type('json')
// => 'application/json'
res.type('application/json')
// => 'application/json'
res.type('png')
// => 'image/png'
res.vary(field)
Adds the field to the Vary
response header, if it is not there already.
res.vary('User-Agent').render('docs')
Router
A router
object is an isolated instance of middleware and routes. You can think of it
as a "mini-application," capable only of performing middleware and routing
functions. Every Express application has a built-in app router.
A router behaves like middleware itself, so you can use it as an argument to app.use() or as the argument to another router’s use() method.
The top-level express
object has a Router() method that creates a new router
object.
Once you’ve created a router object, you can add middleware and HTTP method routes (such as get
, put
, post
,
and so on) to it just like an application. For example:
// invoked for any requests passed to this router
router.use(function (req, res, next) {
// .. some logic here .. like any other middleware
next()
})
// will handle any request that ends in /events
// depends on where the router is "use()'d"
router.get('/events', function (req, res, next) {
// ..
})
You can then use a router for a particular root URL in this way separating your routes into files or even mini-apps.
// only requests to /calendar/* will be sent to our "router"
app.use('/calendar', router)
Methods
router.all(path, [callback, ...] callback)
This method is just like the router.METHOD()
methods, except that it matches all HTTP methods (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 call next()
to continue matching subsequent
routes.
router.all('*', requireAuthentication, loadUser)
Or the equivalent:
router.all('*', requireAuthentication)
router.all('*', loadUser)
Another example of this is white-listed "global" functionality. Here the example is much like before, but it only restricts paths prefixed with "/api":
router.all('/api/*', requireAuthentication)
router.METHOD(path, [callback, ...] callback)
The router.METHOD()
methods provide the routing functionality in Express,
where METHOD is one of the HTTP methods, such as GET, PUT, POST, and so on,
in lowercase. Thus, the actual methods are router.get()
, router.post()
,
router.put()
, and so on.
The router.get()
function is automatically called for the HTTP HEAD
method in
addition to the GET
method if router.head()
was not called for the
path before router.get()
.
You can provide multiple callbacks, and all are treated equally, and behave just
like middleware, except that these callbacks may invoke next('route')
to bypass the remaining route callback(s). You can use this mechanism 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 performing these matches, for example "GET /" would match the following route, as would "GET /?name=tobi".
router.get('/', function (req, res) {
res.send('hello world')
})
You can also use regular expressions—useful if you have very specific constraints, for example the following would match "GET /commits/71dbb9c" as well as "GET /commits/71dbb9c..4c084f9".
router.get(/^\/commits\/(\w+)(?:\.\.(\w+))?$/, function (req, res) {
var from = req.params[0]
var to = req.params[1] || 'HEAD'
res.send('commit range ' + from + '..' + to)
})
router.param(name, callback)
Adds callback triggers to route parameters, where name
is the name of the parameter and callback
is the callback function. Although name
is technically optional, using this method without it is deprecated starting with Express v4.11.0 (see below).
The parameters of the callback function are:
req
, the request object.res
, the response object.next
, indicating the next middleware function.- The value of the
name
parameter. - The name of the parameter.
Unlike app.param()
, router.param()
does not accept an array of 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.
router.param('user', function (req, res, next, id) {
// try to get the user details from the User model and attach it to the request object
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'))
}
})
})
Param callback functions are local to the router on which they are defined. They are not inherited by mounted apps or routers. Hence, param callbacks defined on router
will be triggered only by route parameters defined on router
routes.
A param callback will be called only once in a request-response cycle, even if the parameter is matched in multiple routes, as shown in the following examples.
router.param('id', function (req, res, next, id) {
console.log('CALLED ONLY ONCE')
next()
})
router.get('/user/:id', function (req, res, next) {
console.log('although this matches')
next()
})
router.get('/user/:id', function (req, res) {
console.log('and this matches too')
res.end()
})
On GET /user/42
, the following is printed:
CALLED ONLY ONCE
although this matches
and this matches too
The following section describes router.param(callback)
, which is deprecated as of v4.11.0.
The behavior of the router.param(name, callback)
method can be altered entirely by passing only a function to router.param()
. This function is a custom implementation of how router.param(name, callback)
should behave - it accepts two parameters and must return a middleware.
The first parameter of this function is the name of the URL parameter that should be captured, the second parameter can be any JavaScript object which might be used for returning the middleware implementation.
The middleware returned by the function decides the behavior of what happens when a URL parameter is captured.
In this example, the router.param(name, callback)
signature is modified to router.param(name, accessId)
. Instead of accepting a name and a callback, router.param()
will now accept a name and a number.
var express = require('express')
var app = express()
var router = express.Router()
// customizing the behavior of router.param()
router.param(function (param, option) {
return function (req, res, next, val) {
if (val === option) {
next()
} else {
res.sendStatus(403)
}
}
})
// using the customized router.param()
router.param('id', '1337')
// route to trigger the capture
router.get('/user/:id', function (req, res) {
res.send('OK')
})
app.use(router)
app.listen(3000, function () {
console.log('Ready')
})
In this example, the router.param(name, callback)
signature remains the same, but instead of a middleware callback, a custom data type checking function has been defined to validate the data type of the user id.
router.param(function (param, validator) {
return function (req, res, next, val) {
if (validator(val)) {
next()
} else {
res.sendStatus(403)
}
}
})
router.param('id', function (candidate) {
return !isNaN(parseFloat(candidate)) && isFinite(candidate)
})
router.route(path)
Returns an instance of a single route which you can then use to handle HTTP verbs
with optional middleware. Use router.route()
to avoid duplicate route naming and
thus typing errors.
Building on the router.param()
example above, the following code shows how to use
router.route()
to specify various HTTP method handlers.
var router = express.Router()
router.param('user_id', function (req, res, next, id) {
// sample user, would actually fetch from DB, etc...
req.user = {
id: id,
name: 'TJ'
}
next()
})
router.route('/users/:user_id')
.all(function (req, res, next) {
// runs for all HTTP verbs first
// think of it as route specific middleware!
next()
})
.get(function (req, res, next) {
res.json(req.user)
})
.put(function (req, res, next) {
// just an example of maybe updating the user
req.user.name = req.params.name
// save user ... etc
res.json(req.user)
})
.post(function (req, res, next) {
next(new Error('not implemented'))
})
.delete(function (req, res, next) {
next(new Error('not implemented'))
})
This approach re-uses the single /users/:user_id
path and adds handlers for
various HTTP methods.
NOTE: When you use router.route()
, middleware ordering is based on when the route is created, not when method handlers are added to the route. For this purpose, you can consider method handlers to belong to the route to which they were added.
router.use([path], [function, ...] function)
Uses the specified middleware function or functions, with optional mount path path
, that defaults to "/".
This method is similar to app.use(). A simple example and use case is described below. See app.use() for more information.
Middleware is like a plumbing pipe: requests start at the first middleware function defined and work their way "down" the middleware stack processing for each path they match.
var express = require('express')
var app = express()
var router = express.Router()
// simple logger for this router's requests
// all requests to this router will first hit this middleware
router.use(function (req, res, next) {
console.log('%s %s %s', req.method, req.url, req.path)
next()
})
// this will only be invoked if the path starts with /bar from the mount point
router.use('/bar', function (req, res, next) {
// ... maybe some additional /bar logging ...
next()
})
// always invoked
router.use(function (req, res, next) {
res.send('Hello World')
})
app.use('/foo', router)
app.listen(3000)
The "mount" path is stripped and is not visible to the middleware function. The main effect of this feature is that a mounted middleware function may operate without code changes regardless of its "prefix" pathname.
The order in which you define middleware with router.use()
is very important.
They are invoked sequentially, thus the order defines middleware precedence. For example,
usually a logger is the very first middleware you would use, so that every request gets logged.
var logger = require('morgan')
var path = require('path')
router.use(logger())
router.use(express.static(path.join(__dirname, 'public')))
router.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 the call to express.static()
to the top,
before adding the logger middleware:
router.use(express.static(path.join(__dirname, 'public')))
router.use(logger())
router.use(function (req, res) {
res.send('Hello')
})
Another example is serving files from multiple directories, giving precedence to "./public" over the others:
router.use(express.static(path.join(__dirname, 'public')))
router.use(express.static(path.join(__dirname, 'files')))
router.use(express.static(path.join(__dirname, 'uploads')))
The router.use()
method also supports named parameters so that your mount points
for other routers can benefit from preloading using named parameters.
NOTE: Although these middleware functions are added via a particular router, when they run is defined by the path they are attached to (not the router). Therefore, middleware added via one router may run for other routers if its routes match. For example, this code shows two different routers mounted on the same path:
var authRouter = express.Router()
var openRouter = express.Router()
authRouter.use(require('./authenticate').basic(usersdb))
authRouter.get('/:user_id/edit', function (req, res, next) {
// ... Edit user UI ...
})
openRouter.get('/', function (req, res, next) {
// ... List users ...
})
openRouter.get('/:user_id', function (req, res, next) {
// ... View user ...
})
app.use('/users', authRouter)
app.use('/users', openRouter)
Even though the authentication middleware was added via the authRouter
it will run on the routes defined by the openRouter
as well since both routers were mounted on /users
. To avoid this behavior, use different paths for each router.


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Hi my name is Hristiqn and im a passionate web developer & wanna be designer with just over a year of professional experience. I create pixel perfect web pages & apps with great quality in timely manner.
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