A Subject is a special type of Observable that allows values to be multicasted to many Observers. Subjects are like EventEmitters.

Every Subject is an Observable and an Observer. You can subscribe to a Subject, and you can call next to feed values as well as error and complete.

Type Parameters

  • T

Hierarchy

Implements

Constructors

Properties

closed: boolean
currentObservers: any
hasError: boolean

Deprecated

Internal implementation detail, do not use directly. Will be made internal in v8.

isStopped: boolean

Deprecated

Internal implementation detail, do not use directly. Will be made internal in v8.

observers: <internal>.Observer<T>[]

Deprecated

Internal implementation detail, do not use directly. Will be made internal in v8.

operator: undefined | Operator<any, T>

Deprecated

Internal implementation detail, do not use directly. Will be made internal in v8.

source: undefined | Observable<any>

Deprecated

Internal implementation detail, do not use directly. Will be made internal in v8.

thrownError: any

Deprecated

Internal implementation detail, do not use directly. Will be made internal in v8.

create: ((...args: any[]) => any)

Type declaration

    • (...args: any[]): any
    • Creates a "subject" by basically gluing an observer to an observable.

      Nocollapse

      Deprecated

      Recommended you do not use. Will be removed at some point in the future. Plans for replacement still under discussion.

      Parameters

      • Rest ...args: any[]

      Returns any

Accessors

  • get observed(): boolean
  • Returns boolean

Methods

  • Creates a new Observable with this Subject as the source. You can do this to create customize Observer-side logic of the Subject and conceal it from code that uses the Observable.

    Returns

    Observable that the Subject casts to

    Returns Observable<T>

  • Returns void

  • Parameters

    • err: any

    Returns void

  • Used as a NON-CANCELLABLE means of subscribing to an observable, for use with APIs that expect promises, like async/await. You cannot unsubscribe from this.

    WARNING: Only use this with observables you know will complete. If the source observable does not complete, you will end up with a promise that is hung up, and potentially all of the state of an async function hanging out in memory. To avoid this situation, look into adding something like timeout, take, takeWhile, or takeUntil amongst others.

    Example

    import { interval, take } from 'rxjs';

    const source$ = interval(1000).pipe(take(4));

    async function getTotal() {
    let total = 0;

    await source$.forEach(value => {
    total += value;
    console.log('observable -> ' + value);
    });

    return total;
    }

    getTotal().then(
    total => console.log('Total: ' + total)
    );

    // Expected:
    // 'observable -> 0'
    // 'observable -> 1'
    // 'observable -> 2'
    // 'observable -> 3'
    // 'Total: 6'

    Returns

    a promise that either resolves on observable completion or rejects with the handled error

    Parameters

    • next: ((value: T) => void)

      a handler for each value emitted by the observable

        • (value: T): void
        • Parameters

          • value: T

          Returns void

    Returns Promise<void>

  • Returns

    a promise that either resolves on observable completion or rejects with the handled error

    Deprecated

    Passing a Promise constructor will no longer be available in upcoming versions of RxJS. This is because it adds weight to the library, for very little benefit. If you need this functionality, it is recommended that you either polyfill Promise, or you create an adapter to convert the returned native promise to whatever promise implementation you wanted. Will be removed in v8.

    Parameters

    • next: ((value: T) => void)

      a handler for each value emitted by the observable

        • (value: T): void
        • Parameters

          • value: T

          Returns void

    • promiseCtor: PromiseConstructorLike

      a constructor function used to instantiate the Promise

    Returns Promise<void>

  • Deprecated

    Internal implementation detail, do not use directly. Will be made internal in v8.

    Type Parameters

    • R

    Parameters

    Returns Observable<R>

  • Parameters

    • value: T

    Returns void

  • Returns void

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