Class MongoClient

The MongoClient class is a class that allows for making Connections to MongoDB.

Remarks

The programmatically provided options take precedence over the URI options.

Example

import { MongoClient } from 'mongodb';

// Enable command monitoring for debugging
const client = new MongoClient('mongodb://localhost:27017', { monitorCommands: true });

client.on('commandStarted', started => console.log(started));
client.db().collection('pets');
await client.insertOne({ name: 'spot', kind: 'dog' });

Hierarchy

Constructors

Properties

captureRejectionSymbol: typeof captureRejectionSymbol

Value: Symbol.for('nodejs.rejection')

See how to write a custom rejection handler.

Since

v13.4.0, v12.16.0

captureRejections: boolean

Value: boolean

Change the default captureRejections option on all new EventEmitter objects.

Since

v13.4.0, v12.16.0

defaultMaxListeners: number

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.defaultMaxListenersproperty can be used. If this value is not a positive number, a RangeErroris thrown.

Take caution when setting the events.defaultMaxListeners because the change affects allEventEmitter 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 singleEventEmitter, 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'.

Since

v0.11.2

errorMonitor: typeof errorMonitor

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.

Since

v13.6.0, v12.17.0

Accessors

Methods

  • Close the client and its underlying connections

    Parameters

    • force: boolean = false

      Force close, emitting no events

    Returns Promise<void>

  • Create a new Db instance sharing the current socket connections.

    Parameters

    • Optional dbName: string

      The name of the database we want to use. If not provided, use database name from connection string.

    • Optional options: DbOptions

      Optional settings for Db construction

    Returns Db

  • Type Parameters

    • EventKey extends "error" | "timeout" | "close" | "open" | "serverOpening" | "serverClosed" | "serverDescriptionChanged" | "topologyOpening" | "topologyClosed" | "topologyDescriptionChanged" | "connectionPoolCreated" | "connectionPoolClosed" | "connectionPoolCleared" | "connectionPoolReady" | "connectionCreated" | "connectionReady" | "connectionClosed" | "connectionCheckOutStarted" | "connectionCheckOutFailed" | "connectionCheckedOut" | "connectionCheckedIn" | "commandStarted" | "commandSucceeded" | "commandFailed" | "serverHeartbeatStarted" | "serverHeartbeatSucceeded" | "serverHeartbeatFailed"

    Parameters

    Returns boolean

  • Type Parameters

    • EventKey extends "error" | "timeout" | "close" | "open" | "serverOpening" | "serverClosed" | "serverDescriptionChanged" | "topologyOpening" | "topologyClosed" | "topologyDescriptionChanged" | "connectionPoolCreated" | "connectionPoolClosed" | "connectionPoolCleared" | "connectionPoolReady" | "connectionCreated" | "connectionReady" | "connectionClosed" | "connectionCheckOutStarted" | "connectionCheckOutFailed" | "connectionCheckedOut" | "connectionCheckedIn" | "commandStarted" | "commandSucceeded" | "commandFailed" | "serverHeartbeatStarted" | "serverHeartbeatSucceeded" | "serverHeartbeatFailed"

    Parameters

    • type: string | symbol | EventKey

    Returns number

  • Type Parameters

    • EventKey extends "error" | "timeout" | "close" | "open" | "serverOpening" | "serverClosed" | "serverDescriptionChanged" | "topologyOpening" | "topologyClosed" | "topologyDescriptionChanged" | "connectionPoolCreated" | "connectionPoolClosed" | "connectionPoolCleared" | "connectionPoolReady" | "connectionCreated" | "connectionReady" | "connectionClosed" | "connectionCheckOutStarted" | "connectionCheckOutFailed" | "connectionCheckedOut" | "connectionCheckedIn" | "commandStarted" | "commandSucceeded" | "commandFailed" | "serverHeartbeatStarted" | "serverHeartbeatSucceeded" | "serverHeartbeatFailed"

    Parameters

    • event: string | symbol | EventKey

    Returns MongoClientEvents[EventKey][]

  • Type Parameters

    • EventKey extends "error" | "timeout" | "close" | "open" | "serverOpening" | "serverClosed" | "serverDescriptionChanged" | "topologyOpening" | "topologyClosed" | "topologyDescriptionChanged" | "connectionPoolCreated" | "connectionPoolClosed" | "connectionPoolCleared" | "connectionPoolReady" | "connectionCreated" | "connectionReady" | "connectionClosed" | "connectionCheckOutStarted" | "connectionCheckOutFailed" | "connectionCheckedOut" | "connectionCheckedIn" | "commandStarted" | "commandSucceeded" | "commandFailed" | "serverHeartbeatStarted" | "serverHeartbeatSucceeded" | "serverHeartbeatFailed"

    Parameters

    Returns MongoClient

  • Parameters

    • event: CommonEvents
    • listener: ((eventName, listener) => void)
        • (eventName, listener): void
        • Parameters

          Returns void

    Returns MongoClient

  • Parameters

    Returns MongoClient

  • Type Parameters

    • EventKey extends "error" | "timeout" | "close" | "open" | "serverOpening" | "serverClosed" | "serverDescriptionChanged" | "topologyOpening" | "topologyClosed" | "topologyDescriptionChanged" | "connectionPoolCreated" | "connectionPoolClosed" | "connectionPoolCleared" | "connectionPoolReady" | "connectionCreated" | "connectionReady" | "connectionClosed" | "connectionCheckOutStarted" | "connectionCheckOutFailed" | "connectionCheckedOut" | "connectionCheckedIn" | "commandStarted" | "commandSucceeded" | "commandFailed" | "serverHeartbeatStarted" | "serverHeartbeatSucceeded" | "serverHeartbeatFailed"

    Parameters

    Returns MongoClient

  • Parameters

    • event: CommonEvents
    • listener: ((eventName, listener) => void)
        • (eventName, listener): void
        • Parameters

          Returns void

    Returns MongoClient

  • Parameters

    Returns MongoClient

  • Type Parameters

    • EventKey extends "error" | "timeout" | "close" | "open" | "serverOpening" | "serverClosed" | "serverDescriptionChanged" | "topologyOpening" | "topologyClosed" | "topologyDescriptionChanged" | "connectionPoolCreated" | "connectionPoolClosed" | "connectionPoolCleared" | "connectionPoolReady" | "connectionCreated" | "connectionReady" | "connectionClosed" | "connectionCheckOutStarted" | "connectionCheckOutFailed" | "connectionCheckedOut" | "connectionCheckedIn" | "commandStarted" | "commandSucceeded" | "commandFailed" | "serverHeartbeatStarted" | "serverHeartbeatSucceeded" | "serverHeartbeatFailed"

    Parameters

    Returns MongoClient

  • Parameters

    • event: CommonEvents
    • listener: ((eventName, listener) => void)
        • (eventName, listener): void
        • Parameters

          Returns void

    Returns MongoClient

  • Parameters

    Returns MongoClient

  • Type Parameters

    • EventKey extends "error" | "timeout" | "close" | "open" | "serverOpening" | "serverClosed" | "serverDescriptionChanged" | "topologyOpening" | "topologyClosed" | "topologyDescriptionChanged" | "connectionPoolCreated" | "connectionPoolClosed" | "connectionPoolCleared" | "connectionPoolReady" | "connectionCreated" | "connectionReady" | "connectionClosed" | "connectionCheckOutStarted" | "connectionCheckOutFailed" | "connectionCheckedOut" | "connectionCheckedIn" | "commandStarted" | "commandSucceeded" | "commandFailed" | "serverHeartbeatStarted" | "serverHeartbeatSucceeded" | "serverHeartbeatFailed"

    Parameters

    • event: string | symbol | EventKey

    Returns MongoClientEvents[EventKey][]

  • Type Parameters

    • EventKey extends "error" | "timeout" | "close" | "open" | "serverOpening" | "serverClosed" | "serverDescriptionChanged" | "topologyOpening" | "topologyClosed" | "topologyDescriptionChanged" | "connectionPoolCreated" | "connectionPoolClosed" | "connectionPoolCleared" | "connectionPoolReady" | "connectionCreated" | "connectionReady" | "connectionClosed" | "connectionCheckOutStarted" | "connectionCheckOutFailed" | "connectionCheckedOut" | "connectionCheckedIn" | "commandStarted" | "commandSucceeded" | "commandFailed" | "serverHeartbeatStarted" | "serverHeartbeatSucceeded" | "serverHeartbeatFailed"

    Parameters

    • Optional event: string | symbol | EventKey

    Returns MongoClient

  • Creates a new ClientSession. When using the returned session in an operation a corresponding ServerSession will be created.

    Parameters

    Returns ClientSession

    Remarks

    A ClientSession instance may only be passed to operations being performed on the same MongoClient it was started from.

  • Create a new Change Stream, watching for new changes (insertions, updates, replacements, deletions, and invalidations) in this cluster. Will ignore all changes to system collections, as well as the local, admin, and config databases.

    Type Parameters

    Parameters

    • pipeline: Document[] = []

      An array of pipeline stages through which to pass change stream documents. This allows for filtering (using $match) and manipulating the change stream documents.

    • options: ChangeStreamOptions = {}

      Optional settings for the command

    Returns ChangeStream<TSchema, TChange>

    Remarks

    watch() accepts two generic arguments for distinct use cases:

    • The first is to provide the schema that may be defined for all the data within the current cluster
    • The second is to override the shape of the change stream document entirely, if it is not provided the type will default to ChangeStreamDocument of the first argument
  • A convenience method for creating and handling the clean up of a ClientSession. The session will always be ended when the executor finishes.

    Type Parameters

    • T = any

    Parameters

    • executor: WithSessionCallback<T>

      An executor function that all operations using the provided session must be invoked in

    Returns Promise<T>

  • Type Parameters

    • T = any

    Parameters

    Returns Promise<T>

  • Experimental

    Listens once to the abort event on the provided signal.

    Listening to the abort event on abort signals is unsafe and may lead to resource leaks since another third party with the signal can call e.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 that stopImmediatePropagation does 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

    • signal: AbortSignal
    • resource: ((event) => void)
        • (event): void
        • Parameters

          • event: Event

          Returns void

    Returns Disposable

    that removes the abort listener.

    Since

    v20.5.0

  • Returns a copy of the array of listeners for the event named eventName.

    For EventEmitters this behaves exactly the same as calling .listeners on 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

    • emitter: EventEmitter | _DOMEventTarget
    • name: string | symbol

    Returns Function[]

    Since

    v15.2.0, v14.17.0

  • Returns the currently set max amount of listeners.

    For EventEmitters this behaves exactly the same as calling .getMaxListeners on 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

    • emitter: EventEmitter | _DOMEventTarget

    Returns number

    Since

    v19.9.0

  • A class method that returns the number of listeners for the given eventNameregistered on the given emitter.

    import { EventEmitter, listenerCount } from 'node:events';

    const myEmitter = new EventEmitter();
    myEmitter.on('event', () => {});
    myEmitter.on('event', () => {});
    console.log(listenerCount(myEmitter, 'event'));
    // Prints: 2

    Parameters

    • emitter: EventEmitter

      The emitter to query

    • eventName: string | symbol

      The event name

    Returns number

    Since

    v0.9.12

    Deprecated

    Since v3.2.0 - Use listenerCount instead.

  • 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 here

    Returns an AsyncIterator that iterates eventName events. It will throw if the EventEmitter emits 'error'. It removes all listeners when exiting the loop. The value returned by each iteration is an array composed of the emitted event arguments.

    An AbortSignal can 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

    • emitter: EventEmitter
    • eventName: string

      The name of the event being listened for

    • Optional options: StaticEventEmitterOptions

    Returns AsyncIterableIterator<any>

    that iterates eventName events emitted by the emitter

    Since

    v13.6.0, v12.16.0

  • Creates a Promise that is fulfilled when the EventEmitter emits the given event or that is rejected if the EventEmitter emits 'error' while waiting. The Promise will 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 when events.once()is used to wait for another event. If events.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 boom

    An AbortSignal can 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

    • emitter: _NodeEventTarget
    • eventName: string | symbol
    • Optional options: StaticEventEmitterOptions

    Returns Promise<any[]>

    Since

    v11.13.0, v10.16.0

  • Parameters

    • emitter: _DOMEventTarget
    • eventName: string
    • Optional options: StaticEventEmitterOptions

    Returns Promise<any[]>

  • import { setMaxListeners, EventEmitter } from 'node:events';

    const target = new EventTarget();
    const emitter = new EventEmitter();

    setMaxListeners(5, target, emitter);

    Parameters

    • Optional n: number

      A non-negative number. The maximum number of listeners per EventTarget event.

    • Rest ...eventTargets: (EventEmitter | _DOMEventTarget)[]

    Returns void

    Since

    v15.4.0

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