React Hooks for interacting with RxJS Observables and managing subscriptions.

rxjs-react-hooks.ts

import { useEffect, useState } from 'react';
import { Observable } from 'rxjs';

/**
 * A React hook that manages the subscription of a source Observable, and calls event handlers
 * when source emits 'next' and 'error' events.
 *
 * @param source$ an Observable of type T
 * @param nextHandler a function to be called when source$ emits next value
 * @param errorHandler a function to be called if source$ emits error
 */
export function useSubscription<T>(
  source$: Observable<T>,
  nextHandler: (value: T) => void,
  errorHandler?: (err: unknown) => void
) {
  useEffect(() => {
    if (source$) {
      const subscription = source$.subscribe({
        next: nextHandler,
        error: e => {
          errorHandler && errorHandler(e);
          console.log(e);
        }
      });

      return () => subscription.unsubscribe();
    }
  // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [ source$ ]);
}

/**
 * A React hook that receives a source Oobservable, and an initial value.
 * It uses 'useSubscription' under the hood to manage subsription.
 * It returns the value whenever the Observable emits, and the error should that event occur.
 *
 * @param source$ an Observable of type T
 * @param initialValue an initial value of type T. Default is null.
 * @returns [ value: T, error?: uknown ]
 */
export function useObservable<T>(source$: Observable<T>, initialValue?: T): [ T, unknown ] {
  const [ value, setValue ] = useState<T>(initialValue as T || null);
  const [ error, setError ] = useState<unknown>();

  useSubscription(source$, setValue, setError);

  return [ value, error ];
}