--- /dev/null
+import { Operator } from '../Operator';
+import { Subscriber } from '../Subscriber';
+import { Observable } from '../Observable';
+import { MonoTypeOperatorFunction, PartialObserver, TeardownLogic } from '../types';
+import { noop } from '../util/noop';
+import { isFunction } from '../util/isFunction';
+
+/* tslint:disable:max-line-length */
+/** @deprecated Use an observer instead of a complete callback */
+export function tap<T>(next: null | undefined, error: null | undefined, complete: () => void): MonoTypeOperatorFunction<T>;
+/** @deprecated Use an observer instead of an error callback */
+export function tap<T>(next: null | undefined, error: (error: any) => void, complete?: () => void): MonoTypeOperatorFunction<T>;
+/** @deprecated Use an observer instead of a complete callback */
+export function tap<T>(next: (value: T) => void, error: null | undefined, complete: () => void): MonoTypeOperatorFunction<T>;
+export function tap<T>(next?: (x: T) => void, error?: (e: any) => void, complete?: () => void): MonoTypeOperatorFunction<T>;
+export function tap<T>(observer: PartialObserver<T>): MonoTypeOperatorFunction<T>;
+/* tslint:enable:max-line-length */
+
+/**
+ * Perform a side effect for every emission on the source Observable, but return
+ * an Observable that is identical to the source.
+ *
+ * <span class="informal">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.</span>
+ *
+ * 
+ *
+ * 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.
+ *
+ * ## Example
+ * Map every click to the clientX position of that click, while also logging the click event
+ * ```ts
+ * 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));
+ * ```
+ *
+ * @see {@link map}
+ * @see {@link Observable#subscribe}
+ *
+ * @param {Observer|function} [nextOrObserver] A normal Observer object or a
+ * callback for `next`.
+ * @param {function} [error] Callback for errors in the source.
+ * @param {function} [complete] Callback for the completion of the source.
+ * @return {Observable} An Observable identical to the source, but runs the
+ * specified Observer or callback(s) for each item.
+ * @name tap
+ */
+export function tap<T>(nextOrObserver?: PartialObserver<T> | ((x: T) => void),
+ error?: (e: any) => void,
+ complete?: () => void): MonoTypeOperatorFunction<T> {
+ return function tapOperatorFunction(source: Observable<T>): Observable<T> {
+ return source.lift(new DoOperator(nextOrObserver, error, complete));
+ };
+}
+
+class DoOperator<T> implements Operator<T, T> {
+ constructor(private nextOrObserver?: PartialObserver<T> | ((x: T) => void),
+ private error?: (e: any) => void,
+ private complete?: () => void) {
+ }
+ call(subscriber: Subscriber<T>, source: any): TeardownLogic {
+ return source.subscribe(new TapSubscriber(subscriber, this.nextOrObserver, this.error, this.complete));
+ }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+
+class TapSubscriber<T> extends Subscriber<T> {
+ private _context: any;
+
+ private _tapNext: ((value: T) => void) = noop;
+
+ private _tapError: ((err: any) => void) = noop;
+
+ private _tapComplete: (() => void) = noop;
+
+ constructor(destination: Subscriber<T>,
+ observerOrNext?: PartialObserver<T> | ((value: T) => void),
+ error?: (e?: any) => void,
+ complete?: () => void) {
+ super(destination);
+ this._tapError = error || noop;
+ this._tapComplete = complete || noop;
+ if (isFunction(observerOrNext)) {
+ this._context = this;
+ this._tapNext = observerOrNext;
+ } else if (observerOrNext) {
+ this._context = observerOrNext;
+ this._tapNext = observerOrNext.next || noop;
+ this._tapError = observerOrNext.error || noop;
+ this._tapComplete = observerOrNext.complete || noop;
+ }
+ }
+
+ _next(value: T) {
+ try {
+ this._tapNext.call(this._context, value);
+ } catch (err) {
+ this.destination.error(err);
+ return;
+ }
+ this.destination.next(value);
+ }
+
+ _error(err: any) {
+ try {
+ this._tapError.call(this._context, err);
+ } catch (err) {
+ this.destination.error(err);
+ return;
+ }
+ this.destination.error(err);
+ }
+
+ _complete() {
+ try {
+ this._tapComplete.call(this._context, );
+ } catch (err) {
+ this.destination.error(err);
+ return;
+ }
+ return this.destination.complete();
+ }
+}
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