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Class ChangeStream<TSchema, TChange>

Creates a new Change Stream instance. Normally created using {@link Collection#watch|Collection.watch()}.

Type parameters

Hierarchy

Index

Events

CHANGE: "change" = CHANGE

Fired for each new matching change in the specified namespace. Attaching a change event listener to a Change Stream will switch the stream into flowing mode. Data will then be passed as soon as it is available.

CLOSE: "close" = CLOSE
END: "end" = END
ERROR: "error" = ERROR
INIT: "init" = INIT
MORE: "more" = MORE
RESPONSE: "response" = RESPONSE
RESUME_TOKEN_CHANGED: "resumeTokenChanged" = RESUME_TOKEN_CHANGED

Emitted each time the change stream stores a new resume token.

Properties

namespace: MongoDBNamespace
options: ChangeStreamOptions & { writeConcern?: undefined }
remarks

WriteConcern can still be present on the options because we inherit options from the client/db/collection. The key must be present on the options in order to delete it. This allows typescript to delete the key but will not allow a writeConcern to be assigned as a property on options.

pipeline: Document[]
streamOptions?: CursorStreamOptions
type: symbol
captureRejectionSymbol: typeof captureRejectionSymbol
captureRejections: boolean

Sets or gets the default captureRejection value for all emitters.

defaultMaxListeners: number
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.

Accessors

  • get closed(): boolean
  • get resumeToken(): unknown
  • The cached resume token that is used to resume after the most recently returned change.

    Returns unknown

Methods

  • [asyncIterator](): AsyncGenerator<TChange, void, void>
  • close(): Promise<void>
  • emit<EventKey>(event: symbol | EventKey, ...args: Parameters<ChangeStreamEvents<TSchema, TChange>[EventKey]>): boolean
  • Type parameters

    • EventKey: "error" | "close" | "response" | "more" | "init" | "change" | "end" | "resumeTokenChanged"

    Parameters

    • event: symbol | EventKey
    • Rest ...args: Parameters<ChangeStreamEvents<TSchema, TChange>[EventKey]>

    Returns boolean

  • eventNames(): string[]
  • getMaxListeners(): number
  • hasNext(): Promise<boolean>
  • Check if there is any document still available in the Change Stream

    Returns Promise<boolean>

  • listenerCount<EventKey>(type: string | symbol | EventKey): number
  • listeners<EventKey>(event: string | symbol | EventKey): ChangeStreamEvents<TSchema, TChange>[EventKey][]
  • next(): Promise<TChange>
  • rawListeners<EventKey>(event: string | symbol | EventKey): ChangeStreamEvents<TSchema, TChange>[EventKey][]
  • removeAllListeners<EventKey>(event?: string | symbol | EventKey): ChangeStream<TSchema, TChange>
  • Return a modified Readable stream including a possible transform method.

    NOTE: When using a Stream to process change stream events, the stream will NOT automatically resume in the case a resumable error is encountered.

    throws

    MongoChangeStreamError if the underlying cursor or the change stream is closed

    Parameters

    Returns Readable & AsyncIterable<TChange>

  • tryNext(): Promise<null | TChange>
  • Try to get the next available document from the Change Stream's cursor or null if an empty batch is returned

    Returns Promise<null | TChange>

  • getEventListeners(emitter: EventEmitter | _DOMEventTarget, name: string | symbol): Function[]
  • 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.

    const { getEventListeners, EventEmitter } = require('events');

    {
    const ee = new EventEmitter();
    const listener = () => console.log('Events are fun');
    ee.on('foo', listener);
    getEventListeners(ee, 'foo'); // [listener]
    }
    {
    const et = new EventTarget();
    const listener = () => console.log('Events are fun');
    et.addEventListener('foo', listener);
    getEventListeners(et, 'foo'); // [listener]
    }
    since

    v15.2.0, v14.17.0

    Parameters

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

    Returns Function[]

  • listenerCount(emitter: EventEmitter, eventName: string | symbol): number
  • A class method that returns the number of listeners for the given eventNameregistered on the given emitter.

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

    v0.9.12

    deprecated

    Since v3.2.0 - Use listenerCount instead.

    Parameters

    • emitter: EventEmitter

      The emitter to query

    • eventName: string | symbol

      The event name

    Returns number

  • on(emitter: EventEmitter, eventName: string, options?: StaticEventEmitterOptions): AsyncIterableIterator<any>
  • const { on, EventEmitter } = require('events');
    

    (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')) { // 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:

    ```js
    const { on, EventEmitter } = require('events');
    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());
    since

    v13.6.0, v12.16.0

    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

  • once(emitter: _NodeEventTarget, eventName: string | symbol, options?: StaticEventEmitterOptions): Promise<any[]>
  • once(emitter: _DOMEventTarget, eventName: string, options?: StaticEventEmitterOptions): Promise<any[]>
  • 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.

    const { once, EventEmitter } = require('events');

    async function run() {
    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.log('error happened', err);
    }
    }

    run();

    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:

    const { EventEmitter, once } = require('events');

    const ee = new EventEmitter();

    once(ee, 'error')
    .then(([err]) => console.log('ok', err.message))
    .catch((err) => console.log('error', err.message));

    ee.emit('error', new Error('boom'));

    // Prints: ok boom

    An AbortSignal can be used to cancel waiting for the event:

    const { EventEmitter, once } = require('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!
    since

    v11.13.0, v10.16.0

    Parameters

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

    Returns Promise<any[]>

  • Parameters

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

    Returns Promise<any[]>

  • setMaxListeners(n?: number, ...eventTargets: (EventEmitter | _DOMEventTarget)[]): void
  • const {
    setMaxListeners,
    EventEmitter
    } = require('events');

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

    setMaxListeners(5, target, emitter); ```

    since

    v15.4.0

    Parameters

    • Optional n: number

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

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

    Returns void

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