SessionPool
Hierarchy
- EventEmitter
- SessionPool
Index
Properties
Accessors
Methods
- [captureRejectionSymbol]
- addListener
- addSession
- emit
- eventNames
- getMaxListeners
- getSession
- getState
- initialize
- listenerCount
- listeners
- off
- on
- once
- persistState
- prependListener
- prependOnceListener
- rawListeners
- removeAllListeners
- removeListener
- resetStore
- setMaxListeners
- teardown
- addAbortListener
- getEventListeners
- getMaxListeners
- listenerCount
- on
- once
- open
- setMaxListeners
Properties
readonlyconfig
staticexternalreadonlycaptureRejectionSymbol
Value: Symbol.for('nodejs.rejection')
See how to write a custom rejection handler.
staticexternalcaptureRejections
Value: boolean
Change the default captureRejections option on all new EventEmitter objects.
staticexternaldefaultMaxListeners
By default, a maximum of 10 listeners can be registered for any single
event. This limit can be changed for individual EventEmitter instances
using the emitter.setMaxListeners(n) method. To change the default
for allEventEmitter instances, the events.defaultMaxListeners property
can be used. If this value is not a positive number, a RangeError is thrown.
Take caution when setting the events.defaultMaxListeners because the
change affects all EventEmitter instances, including those created before
the change is made. However, calling emitter.setMaxListeners(n) still has
precedence over events.defaultMaxListeners.
This is not a hard limit. The EventEmitter instance will allow
more listeners to be added but will output a trace warning to stderr indicating
that a "possible EventEmitter memory leak" has been detected. For any single
EventEmitter, the emitter.getMaxListeners() and emitter.setMaxListeners() methods can be used to
temporarily avoid this warning:
import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.setMaxListeners(emitter.getMaxListeners() + 1);
emitter.once('event', () => {
// do stuff
emitter.setMaxListeners(Math.max(emitter.getMaxListeners() - 1, 0));
});
The --trace-warnings command-line flag can be used to display the
stack trace for such warnings.
The emitted warning can be inspected with process.on('warning') and will
have the additional emitter, type, and count properties, referring to
the event emitter instance, the event's name and the number of attached
listeners, respectively.
Its name property is set to 'MaxListenersExceededWarning'.
staticexternalreadonlyerrorMonitor
This symbol shall be used to install a listener for only monitoring 'error' events. Listeners installed using this symbol are called before the regular 'error' listeners are called.
Installing a listener using this symbol does not change the behavior once an 'error' event is emitted. Therefore, the process will still crash if no
regular 'error' listener is installed.
Accessors
retiredSessionsCount
Gets count of retired sessions in the pool.
Returns number
usableSessionsCount
Gets count of usable sessions in the pool.
Returns number
Methods
externaloptional[captureRejectionSymbol]
Type parameters
- K
Parameters
externalerror: Error
externalevent: string | symbol
externalrest...args: AnyRest
Returns void
externaladdListener
Alias for
emitter.on(eventName, listener).Type parameters
- K
Parameters
externaleventName: string | symbol
externallistener: (...args: any[]) => void
Returns this
addSession
Adds a new session to the session pool. The pool automatically creates sessions up to the maximum size of the pool, but this allows you to add more sessions once the max pool size is reached. This also allows you to add session with overridden session options (e.g. with specific session id).
Parameters
optionaloptions: Session | SessionOptions = {}
The configuration options for the session being added to the session pool.
Returns Promise<void>
externalemit
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
trueif the event had listeners,falseotherwise.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 listenerType parameters
- K
Parameters
externaleventName: string | symbol
externalrest...args: AnyRest
Returns boolean
externaleventNames
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) ]Returns (string | symbol)[]
externalgetMaxListeners
Returns the current max listener value for the
EventEmitterwhich is either set byemitter.setMaxListeners(n)or defaults to defaultMaxListeners.Returns number
getSession
Gets session. If there is space for new session, it creates and returns new session. If the session pool is full, it picks a session from the pool, If the picked session is usable it is returned, otherwise it creates and returns a new one.
Returns Promise<Session>
getState
Returns an object representing the internal state of the
SessionPoolinstance. Note that the object's fields can change in future releases.Returns { retiredSessionsCount: number; sessions: SessionState[]; usableSessionsCount: number }
retiredSessionsCount: number
sessions: SessionState[]
usableSessionsCount: number
initialize
Starts periodic state persistence and potentially loads SessionPool state from KeyValueStore. It is called automatically by the SessionPool.open function.
Returns Promise<void>
externallistenerCount
Returns the number of listeners listening for the event named
eventName. Iflisteneris provided, it will return how many times the listener is found in the list of the listeners of the event.Type parameters
- K
Parameters
externaleventName: string | symbol
The name of the event being listened for
externaloptionallistener: Function
The event handler function
Returns number
externallisteners
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] ]Type parameters
- K
Parameters
externaleventName: string | symbol
Returns Function[]
externaloff
Alias for
emitter.removeListener().Type parameters
- K
Parameters
externaleventName: string | symbol
externallistener: (...args: any[]) => void
Returns this
externalon
Adds the
listenerfunction to the end of the listeners array for the event namedeventName. No checks are made to see if thelistenerhas already been added. Multiple calls passing the same combination ofeventNameandlistenerwill result in thelistenerbeing added, and called, multiple times.server.on('connection', (stream) => {
console.log('someone connected!');
});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.prependListener()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.on('foo', () => console.log('a'));
myEE.prependListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// aType parameters
- K
Parameters
externaleventName: string | symbol
The name of the event.
externallistener: (...args: any[]) => void
The callback function
Returns this
externalonce
Adds a one-time
listenerfunction for the event namedeventName. The next timeeventNameis 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
// aType parameters
- K
Parameters
externaleventName: string | symbol
The name of the event.
externallistener: (...args: any[]) => void
The callback function
Returns this
persistState
Persists the current state of the
SessionPoolinto the default KeyValueStore. The state is persisted automatically in regular intervals.Parameters
optionaloptions: PersistenceOptions
Override the persistence options provided in the constructor
Returns Promise<void>
externalprependListener
Adds the
listenerfunction to the beginning of the listeners array for the event namedeventName. No checks are made to see if thelistenerhas already been added. Multiple calls passing the same combination ofeventNameandlistenerwill result in thelistenerbeing 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.Type parameters
- K
Parameters
externaleventName: string | symbol
The name of the event.
externallistener: (...args: any[]) => void
The callback function
Returns this
externalprependOnceListener
Adds a one-time
listenerfunction for the event namedeventNameto the beginning of the listeners array. The next timeeventNameis 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.Type parameters
- K
Parameters
externaleventName: string | symbol
The name of the event.
externallistener: (...args: any[]) => void
The callback function
Returns this
externalrawListeners
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');Type parameters
- K
Parameters
externaleventName: string | symbol
Returns Function[]
externalremoveAllListeners
Removes all listeners, or those of the specified
eventName.It is bad practice to remove listeners added elsewhere in the code, particularly when the
EventEmitterinstance 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.Parameters
externaloptionaleventName: string | symbol
Returns this
externalremoveListener
Removes the specified
listenerfrom the listener array for the event namedeventName.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 specifiedeventName, thenremoveListener()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()orremoveAllListeners()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:
// ABecause 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 theonce('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.Type parameters
- K
Parameters
externaleventName: string | symbol
externallistener: (...args: any[]) => void
Returns this
resetStore
Parameters
optionaloptions: PersistenceOptions
Override the persistence options provided in the constructor
Returns Promise<void>
externalsetMaxListeners
By default
EventEmitters will print a warning if more than10listeners are added for a particular event. This is a useful default that helps finding memory leaks. Theemitter.setMaxListeners()method allows the limit to be modified for this specificEventEmitterinstance. The value can be set toInfinity(or0) to indicate an unlimited number of listeners.Returns a reference to the
EventEmitter, so that calls can be chained.Parameters
externaln: number
Returns this
teardown
Removes listener from
persistStateevent. This function should be called after you are done with using theSessionPoolinstance.Returns Promise<void>
staticexternaladdAbortListener
- experimental
Listens once to the
abortevent on the providedsignal.Listening to the
abortevent on abort signals is unsafe and may lead to resource leaks since another third party with the signal can calle.stopImmediatePropagation(). Unfortunately Node.js cannot change this since it would violate the web standard. Additionally, the original API makes it easy to forget to remove listeners.This API allows safely using
AbortSignals in Node.js APIs by solving these two issues by listening to the event such thatstopImmediatePropagationdoes not prevent the listener from running.Returns a disposable so that it may be unsubscribed from more easily.
import { addAbortListener } from 'node:events';
function example(signal) {
let disposable;
try {
signal.addEventListener('abort', (e) => e.stopImmediatePropagation());
disposable = addAbortListener(signal, (e) => {
// Do something when signal is aborted.
});
} finally {
disposable?.[Symbol.dispose]();
}
}Parameters
externalsignal: AbortSignal
externalresource: (event: Event) => void
Returns Disposable
Disposable that removes the
abortlistener.
staticexternalgetEventListeners
Returns a copy of the array of listeners for the event named
eventName.For
EventEmitters this behaves exactly the same as calling.listenerson the emitter.For
EventTargets this is the only way to get the event listeners for the event target. This is useful for debugging and diagnostic purposes.import { getEventListeners, EventEmitter } from 'node:events';
{
const ee = new EventEmitter();
const listener = () => console.log('Events are fun');
ee.on('foo', listener);
console.log(getEventListeners(ee, 'foo')); // [ [Function: listener] ]
}
{
const et = new EventTarget();
const listener = () => console.log('Events are fun');
et.addEventListener('foo', listener);
console.log(getEventListeners(et, 'foo')); // [ [Function: listener] ]
}Parameters
externalemitter: EventEmitter<DefaultEventMap> | EventTarget
externalname: string | symbol
Returns Function[]
staticexternalgetMaxListeners
Returns the currently set max amount of listeners.
For
EventEmitters this behaves exactly the same as calling.getMaxListenerson the emitter.For
EventTargets this is the only way to get the max event listeners for the event target. If the number of event handlers on a single EventTarget exceeds the max set, the EventTarget will print a warning.import { getMaxListeners, setMaxListeners, EventEmitter } from 'node:events';
{
const ee = new EventEmitter();
console.log(getMaxListeners(ee)); // 10
setMaxListeners(11, ee);
console.log(getMaxListeners(ee)); // 11
}
{
const et = new EventTarget();
console.log(getMaxListeners(et)); // 10
setMaxListeners(11, et);
console.log(getMaxListeners(et)); // 11
}Parameters
externalemitter: EventEmitter<DefaultEventMap> | EventTarget
Returns number
staticexternallistenerCount
A class method that returns the number of listeners for the given
eventNameregistered on the givenemitter.import { EventEmitter, listenerCount } from 'node:events';
const myEmitter = new EventEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(listenerCount(myEmitter, 'event'));
// Prints: 2Parameters
externalemitter: EventEmitter<DefaultEventMap>
The emitter to query
externaleventName: string | symbol
The event name
Returns number
staticexternalon
import { on, EventEmitter } from 'node:events';
import process from 'node:process';
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo')) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable hereReturns an
AsyncIteratorthat iterateseventNameevents. It will throw if theEventEmitteremits'error'. It removes all listeners when exiting the loop. Thevaluereturned by each iteration is an array composed of the emitted event arguments.An
AbortSignalcan be used to cancel waiting on events:import { on, EventEmitter } from 'node:events';
import process from 'node:process';
const ac = new AbortController();
(async () => {
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo', { signal: ac.signal })) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
})();
process.nextTick(() => ac.abort());Parameters
externalemitter: EventEmitter<DefaultEventMap>
externaleventName: string
The name of the event being listened for
externaloptionaloptions: StaticEventEmitterOptions
Returns AsyncIterableIterator<any>
An
AsyncIteratorthat iterateseventNameevents emitted by theemitter
staticexternalonce
Creates a
Promisethat is fulfilled when theEventEmitteremits the given event or that is rejected if theEventEmitteremits'error'while waiting. ThePromisewill resolve with an array of all the arguments emitted to the given event.This method is intentionally generic and works with the web platform EventTarget interface, which has no special
'error'event semantics and does not listen to the'error'event.import { once, EventEmitter } from 'node:events';
import process from 'node:process';
const ee = new EventEmitter();
process.nextTick(() => {
ee.emit('myevent', 42);
});
const [value] = await once(ee, 'myevent');
console.log(value);
const err = new Error('kaboom');
process.nextTick(() => {
ee.emit('error', err);
});
try {
await once(ee, 'myevent');
} catch (err) {
console.error('error happened', err);
}The special handling of the
'error'event is only used whenevents.once()is used to wait for another event. Ifevents.once()is used to wait for the 'error'event itself, then it is treated as any other kind of event without special handling:import { EventEmitter, once } from 'node:events';
const ee = new EventEmitter();
once(ee, 'error')
.then(([err]) => console.log('ok', err.message))
.catch((err) => console.error('error', err.message));
ee.emit('error', new Error('boom'));
// Prints: ok boomAn
AbortSignalcan be used to cancel waiting for the event:import { EventEmitter, once } from 'node:events';
const ee = new EventEmitter();
const ac = new AbortController();
async function foo(emitter, event, signal) {
try {
await once(emitter, event, { signal });
console.log('event emitted!');
} catch (error) {
if (error.name === 'AbortError') {
console.error('Waiting for the event was canceled!');
} else {
console.error('There was an error', error.message);
}
}
}
foo(ee, 'foo', ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!Parameters
externalemitter: EventEmitter<DefaultEventMap>
externaleventName: string | symbol
externaloptionaloptions: StaticEventEmitterOptions
Returns Promise<any[]>
staticopen
Opens a SessionPool and returns a promise resolving to an instance of the SessionPool class that is already initialized.
For more details and code examples, see the SessionPool class.
Parameters
optionaloptions: SessionPoolOptions
optionalconfig: Configuration
Returns Promise<SessionPool>
staticexternalsetMaxListeners
import { setMaxListeners, EventEmitter } from 'node:events';
const target = new EventTarget();
const emitter = new EventEmitter();
setMaxListeners(5, target, emitter);Parameters
externaloptionaln: number
A non-negative number. The maximum number of listeners per
EventTargetevent.externalrest...eventTargets: (EventEmitter<DefaultEventMap> | EventTarget)[]
Returns void
Handles the rotation, creation and persistence of user-like sessions. Creates a pool of Session instances, that are randomly rotated. When some session is marked as blocked, it is removed and new one is created instead (the pool never returns an unusable session). Learn more in the Session management guide.
You can create one by calling the SessionPool.open function.
Session pool is already integrated into crawlers, and it can significantly improve your scraper performance with just 2 lines of code.
Example usage:
You can configure the pool with many options. See the SessionPoolOptions. Session pool is by default persisted in default KeyValueStore. If you want to have one pool for all runs you have to specify SessionPoolOptions.persistStateKeyValueStoreId.
Advanced usage:
*Default session allocation flow:
SessionPoolreachesmaxPoolSize, new sessions are created, provided to the user and added to the poolmaxPoolSize), a random session from the pool is provided.