function
stable
Perform a side effect for every emission on the source Observable, but return an Observable that is identical to the source.
tap<T>(nextOrObserver?: PartialObserver<T> | ((x: T) => void), error?: (e: any) => void, complete?: () => void): MonoTypeOperatorFunction<T>
nextOrObserver | Optional. Default is A normal Observer object or a callback for |
error | Optional. Default is Callback for errors in the source. |
complete | Optional. Default is Callback for the completion of the source. |
MonoTypeOperatorFunction<T>
: An Observable identical to the source, but runs the specified Observer or callback(s) for each item.
Intercepts each emission on the source and runs a function, but returns an output which is identical to the source as long as errors don't occur.
Returns a mirrored Observable of the source Observable, but modified so that the provided Observer is called to perform a side effect for every value, error, and completion emitted by the source. Any errors that are thrown in the aforementioned Observer or handlers are safely sent down the error path of the output Observable.
This operator is useful for debugging your Observables for the correct values or performing other side effects.
Note: this is different to a subscribe
on the Observable. If the Observable returned by tap
is not subscribed, the side effects specified by the Observer will never happen. tap
therefore simply spies on existing execution, it does not trigger an execution to happen like subscribe
does.
Map every click to the clientX position of that click, while also logging the click event
import { fromEvent } from 'rxjs'; import { tap, map } from 'rxjs/operators'; const clicks = fromEvent(document, 'click'); const positions = clicks.pipe( tap(ev => console.log(ev)), map(ev => ev.clientX), ); positions.subscribe(x => console.log(x));
tap(next: null | undefined, error: null | undefined, complete: () => void): MonoTypeOperatorFunction<T>
next | Type: |
error | Type: |
complete | Type: |
MonoTypeOperatorFunction<T>
tap(next: null | undefined, error: (error: any) => void, complete?: () => void): MonoTypeOperatorFunction<T>
next | Type: |
error | Type: |
complete | Optional. Default is Type: |
MonoTypeOperatorFunction<T>
tap(next: (value: T) => void, error: null | undefined, complete: () => void): MonoTypeOperatorFunction<T>
next | Type: |
error | Type: |
complete | Type: |
MonoTypeOperatorFunction<T>
tap(next?: (x: T) => void, error?: (e: any) => void, complete?: () => void): MonoTypeOperatorFunction<T>
next | Optional. Default is Type: |
error | Optional. Default is Type: |
complete | Optional. Default is Type: |
MonoTypeOperatorFunction<T>
tap(observer: PartialObserver<T>): MonoTypeOperatorFunction<T>
observer | Type: |
MonoTypeOperatorFunction<T>
© 2015–2018 Google, Inc., Netflix, Inc., Microsoft Corp. and contributors.
Code licensed under an Apache-2.0 License. Documentation licensed under CC BY 4.0.
https://rxjs.dev/api/operators/tap