Express instance itself is a request handler, which could be invoked without third argument.
Used to get all registered routes in Express Application
Special-cased "all" method, applying the given route path,
middleware, and callback to every HTTP method.
The app.mountpath property contains one or more path patterns on which a sub-app was mounted.
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:
The app.routes object houses all of the routes defined mapped by the associated HTTP verb. This object may be used for introspection capabilities, for example Express uses this internally not only for routing but to provide default OPTIONS behaviour unless app.options() is used. Your application or framework may also remove routes by simply by removing them from this object.
Stack of configured routes
Optional [captureAlias for emitter.on(eventName, listener).
v0.1.26
Synchronously calls each of the listeners registered for the event named eventName, in the order they were registered, passing the supplied arguments
to each.
Returns true if the event had listeners, false otherwise.
import { EventEmitter } from 'node:events';
const myEmitter = new EventEmitter();
// First listener
myEmitter.on('event', function firstListener() {
console.log('Helloooo! first listener');
});
// Second listener
myEmitter.on('event', function secondListener(arg1, arg2) {
console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
});
// Third listener
myEmitter.on('event', function thirdListener(...args) {
const parameters = args.join(', ');
console.log(`event with parameters ${parameters} in third listener`);
});
console.log(myEmitter.listeners('event'));
myEmitter.emit('event', 1, 2, 3, 4, 5);
// Prints:
// [
// [Function: firstListener],
// [Function: secondListener],
// [Function: thirdListener]
// ]
// Helloooo! first listener
// event with parameters 1, 2 in second listener
// event with parameters 1, 2, 3, 4, 5 in third listener
Rest ...args: AnyRestv0.1.26
Register the given template engine callback fn
as ext.
By default will require() the engine based on the
file extension. For example if you try to render
a "foo.jade" file Express will invoke the following internally:
app.engine('jade', require('jade').__express);
For engines that do not provide .__express out of the box,
or if you wish to "map" a different extension to the template engine
you may use this method. For example mapping the EJS template engine to
".html" files:
app.engine('html', require('ejs').renderFile);
In this case EJS provides a .renderFile() method with
the same signature that Express expects: (path, options, callback),
though note that it aliases this method as ejs.__express internally
so if you're using ".ejs" extensions you dont need to do anything.
Some template engines do not follow this convention, the Consolidate.js library was created to map all of node's popular template engines to follow this convention, thus allowing them to work seamlessly within Express.
Returns an array listing the events for which the emitter has registered
listeners. The values in the array are strings or Symbols.
import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});
const sym = Symbol('symbol');
myEE.on(sym, () => {});
console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]
v6.0.0
Listen for connections.
A node http.Server is returned, with this
application (which is a Function) as its
callback. If you wish to create both an HTTP
and HTTPS server you may do so with the "http"
and "https" modules as shown here:
var http = require('http') , https = require('https') , express = require('express') , app = express();
http.createServer(app).listen(80); https.createServer({ ... }, app).listen(443);
Optional callback: ObjectOptional callback: ObjectOptional callback: ObjectOptional callback: ObjectOptional callback: ObjectOptional listeningListener: ObjectReturns the number of listeners listening for the event named eventName.
If listener is provided, it will return how many times the listener is found
in the list of the listeners of the event.
The name of the event being listened for
Optional listener: FunctionThe event handler function
v3.2.0
Returns a copy of the array of listeners for the event named eventName.
server.on('connection', (stream) => {
console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
v0.1.26
Alias for emitter.removeListener().
v10.0.0
Adds a one-time listener function for the event named eventName. The
next time eventName is triggered, this listener is removed and then invoked.
server.once('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the EventEmitter, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The emitter.prependOnceListener() method can be used as an alternative to add the
event listener to the beginning of the listeners array.
import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
The name of the event.
The callback function
v0.3.0
Map the given param placeholder name(s) to the given callback(s).
Parameter mapping is used to provide pre-conditions to routes which use normalized placeholders. For example a :user_id parameter could automatically load a user's information from the database without any additional code,
The callback uses the samesignature as middleware, the only differencing
being that the value of the placeholder is passed, in this case the id
of the user. Once the next() function is invoked, just like middleware
it will continue on to execute the route, or subsequent parameter functions.
app.param('user_id', function(req, res, next, id){
User.find(id, function(err, user){
if (err) {
next(err);
} else if (user) {
req.user = user;
next();
} else {
next(new Error('failed to load user'));
}
});
});
Alternatively, you can pass only a callback, in which case you have the opportunity to alter the app.param()
since version 4.11
Adds the listener function to the beginning of the listeners array for the
event named eventName. No checks are made to see if the listener has
already been added. Multiple calls passing the same combination of eventName
and listener will result in the listener being added, and called, multiple times.
server.prependListener('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the EventEmitter, so that calls can be chained.
The name of the event.
The callback function
v6.0.0
Adds a one-timelistener function for the event named eventName to the beginning of the listeners array. The next time eventName is triggered, this
listener is removed, and then invoked.
server.prependOnceListener('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the EventEmitter, so that calls can be chained.
The name of the event.
The callback function
v6.0.0
Returns a copy of the array of listeners for the event named eventName,
including any wrappers (such as those created by .once()).
import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));
// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];
// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();
// Logs "log once" to the console and removes the listener
logFnWrapper();
emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');
// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');
v9.4.0
Removes all listeners, or those of the specified eventName.
It is bad practice to remove listeners added elsewhere in the code,
particularly when the EventEmitter instance was created by some other
component or module (e.g. sockets or file streams).
Returns a reference to the EventEmitter, so that calls can be chained.
Optional eventName: string | symbolv0.1.26
Removes the specified listener from the listener array for the event named eventName.
const callback = (stream) => {
console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);
removeListener() will remove, at most, one instance of a listener from the
listener array. If any single listener has been added multiple times to the
listener array for the specified eventName, then removeListener() must be
called multiple times to remove each instance.
Once an event is emitted, all listeners attached to it at the
time of emitting are called in order. This implies that any removeListener() or removeAllListeners() calls after emitting and before the last listener finishes execution
will not remove them fromemit() in progress. Subsequent events behave as expected.
import { EventEmitter } from 'node:events';
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
const callbackA = () => {
console.log('A');
myEmitter.removeListener('event', callbackB);
};
const callbackB = () => {
console.log('B');
};
myEmitter.on('event', callbackA);
myEmitter.on('event', callbackB);
// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit('event');
// Prints:
// A
// B
// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit('event');
// Prints:
// A
Because listeners are managed using an internal array, calling this will
change the position indices of any listener registered after the listener
being removed. This will not impact the order in which listeners are called,
but it means that any copies of the listener array as returned by
the emitter.listeners() method will need to be recreated.
When a single function has been added as a handler multiple times for a single
event (as in the example below), removeListener() will remove the most
recently added instance. In the example the once('ping') listener is removed:
import { EventEmitter } from 'node:events';
const ee = new EventEmitter();
function pong() {
console.log('pong');
}
ee.on('ping', pong);
ee.once('ping', pong);
ee.removeListener('ping', pong);
ee.emit('ping');
ee.emit('ping');
Returns a reference to the EventEmitter, so that calls can be chained.
v0.1.26
Render the given view name name with options
and a callback accepting an error and the
rendered template string.
Example:
app.render('email', { name: 'Tobi' }, function(err, html){ // ... })
Optional options: objectOptional callback: ObjectBy default EventEmitters will print a warning if more than 10 listeners are
added for a particular event. This is a useful default that helps finding
memory leaks. The emitter.setMaxListeners() method allows the limit to be
modified for this specific EventEmitter instance. The value can be set to Infinity (or 0) to indicate an unlimited number of listeners.
Returns a reference to the EventEmitter, so that calls can be chained.
v0.3.5
The
EventEmitterclass is defined and exposed by thenode:eventsmodule:All
EventEmitters emit the event'newListener'when new listeners are added and'removeListener'when existing listeners are removed.It supports the following option:
Since
v0.1.26