rxjs/src/internal/operators/OperatorSubscriber.ts

Reactive Extensions for modern JavaScript

/** @prettier */
import { Subscriber } from '../Subscriber';

/**
 * A generic helper for allowing operators to be created with a Subscriber and
 * use closures to capture neceessary state from the operator function itself.
 */
export class OperatorSubscriber<T> extends Subscriber<T> {
  /**
   * Creates an instance of an `OperatorSubscriber`.
   * @param destination The downstream subscriber.
   * @param onNext Handles next values, only called if this subscriber is not stopped or closed. Any
   * error that occurs in this function is caught and sent to the `error` method of this subscriber.
   * @param onError Handles errors from the subscription, any errors that occur in this handler are caught
   * and send to the `destination` error handler.
   * @param onComplete Handles completion notification from the subscription. Any errors that occur in
   * this handler are sent to the `destination` error handler.
   * @param onUnsubscribe Additional teardown logic here. This will only be called on teardown if the
   * subscriber itself is not already closed. Called before any additional teardown logic is called.
   */
  constructor(
    destination: Subscriber<any>,
    onNext?: (value: T) => void,
    onError?: (err: any) => void,
    onComplete?: () => void,
    private onUnsubscribe?: () => void
  ) {
    super(destination);
    if (onNext) {
      this._next = function (value: T) {
        try {
          onNext(value);
        } catch (err) {
          this.destination.error(err);
        }
      };
    }
    if (onError) {
      this._error = function (err) {
        try {
          onError(err);
        } catch (err) {
          // Send any errors that occur down stream.
          this.destination.error(err);
        }
        // Ensure teardown.
        this.unsubscribe();
      };
    }
    if (onComplete) {
      this._complete = function () {
        try {
          onComplete();
        } catch (err) {
          // Send any errors that occur down stream.
          this.destination.error(err);
        }
        // Ensure teardown.
        this.unsubscribe();
      };
    }
  }

  unsubscribe() {
    // Execute additional teardown if we have any and we didn't already do so.
    !this.closed && this.onUnsubscribe?.();
    super.unsubscribe();
  }
}