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import { MonoTypeOperatorFunction, Observer } from '../types';
import { isFunction } from '../util/isFunction';
import { operate } from '../util/lift';
import { createOperatorSubscriber } from './OperatorSubscriber';
import { identity } from '../util/identity';
/**
* An extension to the {@link Observer} interface used only by the {@link tap} operator.
*
* It provides a useful set of callbacks a user can register to do side-effects in
* cases other than what the usual {@link Observer} callbacks are
* ({@link guide/glossary-and-semantics#next next},
* {@link guide/glossary-and-semantics#error error} and/or
* {@link guide/glossary-and-semantics#complete complete}).
*
* ## Example
*
* ```ts
* import { fromEvent, switchMap, tap, interval, take } from 'rxjs';
*
* const source$ = fromEvent(document, 'click');
* const result$ = source$.pipe(
* switchMap((_, i) => i % 2 === 0
* ? fromEvent(document, 'mousemove').pipe(
* tap({
* subscribe: () => console.log('Subscribed to the mouse move events after click #' + i),
* unsubscribe: () => console.log('Mouse move events #' + i + ' unsubscribed'),
* finalize: () => console.log('Mouse move events #' + i + ' finalized')
* })
* )
* : interval(1_000).pipe(
* take(5),
* tap({
* subscribe: () => console.log('Subscribed to the 1-second interval events after click #' + i),
* unsubscribe: () => console.log('1-second interval events #' + i + ' unsubscribed'),
* finalize: () => console.log('1-second interval events #' + i + ' finalized')
* })
* )
* )
* );
*
* const subscription = result$.subscribe({
* next: console.log
* });
*
* setTimeout(() => {
* console.log('Unsubscribe after 60 seconds');
* subscription.unsubscribe();
* }, 60_000);
* ```
*/
export interface TapObserver<T> extends Observer<T> {
/**
* The callback that `tap` operator invokes at the moment when the source Observable
* gets subscribed to.
*/
subscribe: () => void;
/**
* The callback that `tap` operator invokes when an explicit
* {@link guide/glossary-and-semantics#unsubscription unsubscribe} happens. It won't get invoked on
* `error` or `complete` events.
*/
unsubscribe: () => void;
/**
* The callback that `tap` operator invokes when any kind of
* {@link guide/glossary-and-semantics#finalization finalization} happens - either when
* the source Observable `error`s or `complete`s or when it gets explicitly unsubscribed
* by the user. There is no difference in using this callback or the {@link finalize}
* operator, but if you're already using `tap` operator, you can use this callback
* instead. You'd get the same result in either case.
*/
finalize: () => void;
}
export function tap<T>(observerOrNext?: Partial<TapObserver<T>> | ((value: T) => void)): MonoTypeOperatorFunction<T>;
/** @deprecated Instead of passing separate callback arguments, use an observer argument. Signatures taking separate callback arguments will be removed in v8. Details: https://rxjs.dev/deprecations/subscribe-arguments */
export function tap<T>(
next?: ((value: T) => void) | null,
error?: ((error: any) => void) | null,
complete?: (() => void) | null
): MonoTypeOperatorFunction<T>;
/**
* Used to perform side-effects for notifications from the source observable
*
* <span class="informal">Used when you want to affect outside state with a notification without altering the notification</span>
*
* 
*
* Tap is designed to allow the developer a designated place to perform side effects. While you _could_ perform side-effects
* inside of a `map` or a `mergeMap`, that would make their mapping functions impure, which isn't always a big deal, but will
* make it so you can't do things like memoize those functions. The `tap` operator is designed solely for such side-effects to
* help you remove side-effects from other operations.
*
* For any notification, next, error, or complete, `tap` will call the appropriate callback you have provided to it, via a function
* reference, or a partial observer, then pass that notification down the stream.
*
* The observable returned by `tap` is an exact mirror of the source, with one exception: Any error that occurs -- synchronously -- in a handler
* provided to `tap` will be emitted as an error from the returned observable.
*
* > Be careful! You can mutate objects as they pass through the `tap` operator's handlers.
*
* The most common use of `tap` is actually for debugging. You can place a `tap(console.log)` anywhere
* in your observable `pipe`, log out the notifications as they are emitted by the source returned by the previous
* operation.
*
* ## Examples
*
* Check a random number before it is handled. Below is an observable that will use a random number between 0 and 1,
* and emit `'big'` or `'small'` depending on the size of that number. But we wanted to log what the original number
* was, so we have added a `tap(console.log)`.
*
* ```ts
* import { of, tap, map } from 'rxjs';
*
* of(Math.random()).pipe(
* tap(console.log),
* map(n => n > 0.5 ? 'big' : 'small')
* ).subscribe(console.log);
* ```
*
* Using `tap` to analyze a value and force an error. Below is an observable where in our system we only
* want to emit numbers 3 or less we get from another source. We can force our observable to error
* using `tap`.
*
* ```ts
* import { of, tap } from 'rxjs';
*
* const source = of(1, 2, 3, 4, 5);
*
* source.pipe(
* tap(n => {
* if (n > 3) {
* throw new TypeError(`Value ${ n } is greater than 3`);
* }
* })
* )
* .subscribe({ next: console.log, error: err => console.log(err.message) });
* ```
*
* We want to know when an observable completes before moving on to the next observable. The system
* below will emit a random series of `'X'` characters from 3 different observables in sequence. The
* only way we know when one observable completes and moves to the next one, in this case, is because
* we have added a `tap` with the side effect of logging to console.
*
* ```ts
* import { of, concatMap, interval, take, map, tap } from 'rxjs';
*
* of(1, 2, 3).pipe(
* concatMap(n => interval(1000).pipe(
* take(Math.round(Math.random() * 10)),
* map(() => 'X'),
* tap({ complete: () => console.log(`Done with ${ n }`) })
* ))
* )
* .subscribe(console.log);
* ```
*
* @see {@link finalize}
* @see {@link TapObserver}
*
* @param observerOrNext A next handler or partial observer
* @param error An error handler
* @param complete A completion handler
* @return A function that returns an Observable identical to the source, but
* runs the specified Observer or callback(s) for each item.
*/
export function tap<T>(
observerOrNext?: Partial<TapObserver<T>> | ((value: T) => void) | null,
error?: ((e: any) => void) | null,
complete?: (() => void) | null
): MonoTypeOperatorFunction<T> {
// We have to check to see not only if next is a function,
// but if error or complete were passed. This is because someone
// could technically call tap like `tap(null, fn)` or `tap(null, null, fn)`.
const tapObserver =
isFunction(observerOrNext) || error || complete
? // tslint:disable-next-line: no-object-literal-type-assertion
({ next: observerOrNext as Exclude<typeof observerOrNext, Partial<TapObserver<T>>>, error, complete } as Partial<TapObserver<T>>)
: observerOrNext;
return tapObserver
? operate((source, subscriber) => {
tapObserver.subscribe?.();
let isUnsub = true;
source.subscribe(
createOperatorSubscriber(
subscriber,
(value) => {
tapObserver.next?.(value);
subscriber.next(value);
},
() => {
isUnsub = false;
tapObserver.complete?.();
subscriber.complete();
},
(err) => {
isUnsub = false;
tapObserver.error?.(err);
subscriber.error(err);
},
() => {
if (isUnsub) {
tapObserver.unsubscribe?.();
}
tapObserver.finalize?.();
}
)
);
})
: // Tap was called with no valid tap observer or handler
// (e.g. `tap(null, null, null)` or `tap(null)` or `tap()`)
// so we're going to just mirror the source.
identity;
}