import { MonoTypeOperatorFunction, Observer } from '../types';
|
import { isFunction } from '../util/isFunction';
|
import { operate } from '../util/lift';
|
import { createOperatorSubscriber } from './OperatorSubscriber';
|
import { identity } from '../util/identity';
|
|
export interface TapObserver<T> extends Observer<T> {
|
subscribe: () => void;
|
unsubscribe: () => void;
|
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 Observable#subscribe}
|
*
|
* @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;
|
}
|