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PATH: usr / local / lib / node_modules / ghost-cli / node_modules / rxjs / src / internal / operators

import { Observable } from '../Observable';
import { Operator } from '../Operator';
import { Subscriber } from '../Subscriber';
import { EmptyError } from '../util/EmptyError';
import { OperatorFunction } from '../../internal/types';
import { filter } from './filter';
import { take } from './take';
import { defaultIfEmpty } from './defaultIfEmpty';
import { throwIfEmpty } from './throwIfEmpty';
import { identity } from '../util/identity';

/* tslint:disable:max-line-length */
export function first<T, D = T>(
  predicate?: null,
  defaultValue?: D
): OperatorFunction<T, T | D>;
export function first<T, S extends T>(
  predicate: (value: T, index: number, source: Observable<T>) => value is S,
  defaultValue?: S
): OperatorFunction<T, S>;
export function first<T, D = T>(
  predicate: (value: T, index: number, source: Observable<T>) => boolean,
  defaultValue?: D
): OperatorFunction<T, T | D>;
/* tslint:enable:max-line-length */

/**
 * Emits only the first value (or the first value that meets some condition)
 * emitted by the source Observable.
 *
 * <span class="informal">Emits only the first value. Or emits only the first
 * value that passes some test.</span>
 *
 * ![](first.png)
 *
 * If called with no arguments, `first` emits the first value of the source
 * Observable, then completes. If called with a `predicate` function, `first`
 * emits the first value of the source that matches the specified condition. It
 * may also take a deprecated `resultSelector` function to produce the output
 * value from the input value, and a `defaultValue` to emit in case the source
 * completes before it is able to emit a valid value. Throws an error if
 * `defaultValue` was not provided and a matching element is not found.
 *
 * ## Examples
 * Emit only the first click that happens on the DOM
 * ```ts
 * import { fromEvent } from 'rxjs';
 * import { first } from 'rxjs/operators';
 *
 * const clicks = fromEvent(document, 'click');
 * const result = clicks.pipe(first());
 * result.subscribe(x => console.log(x));
 * ```
 *
 * Emits the first click that happens on a DIV
 * ```ts
 * import { fromEvent } from 'rxjs';
 * import { first } from 'rxjs/operators';
 *
 * const clicks = fromEvent(document, 'click');
 * const result = clicks.pipe(first(ev => ev.target.tagName === 'DIV'));
 * result.subscribe(x => console.log(x));
 * ```
 *
 * @see {@link filter}
 * @see {@link find}
 * @see {@link take}
 *
 * @throws {EmptyError} Delivers an EmptyError to the Observer's `error`
 * callback if the Observable completes before any `next` notification was sent.
 *
 * @param {function(value: T, index: number, source: Observable<T>): boolean} [predicate]
 * An optional function called with each item to test for condition matching.
 * @param {R} [defaultValue] The default value emitted in case no valid value
 * was found on the source.
 * @return {Observable<T|R>} An Observable of the first item that matches the
 * condition.
 * @method first
 * @owner Observable
 */
export function first<T, D>(
  predicate?: ((value: T, index: number, source: Observable<T>) => boolean) | null,
  defaultValue?: D
): OperatorFunction<T, T | D> {
  const hasDefaultValue = arguments.length >= 2;
  return (source: Observable<T>) => source.pipe(
    predicate ? filter((v, i) => predicate(v, i, source)) : identity,
    take(1),
    hasDefaultValue ? defaultIfEmpty<T | D>(defaultValue) : throwIfEmpty(() => new EmptyError()),
  );
}

[-] toArray.ts [edit]
[-] window.ts [edit]
[-] retry.ts [edit]
[-] mergeAll.ts [edit]
[-] windowWhen.ts [edit]
[-] every.ts [edit]
[-] timeout.ts [edit]
[-] debounceTime.ts [edit]
[-] index.ts [edit]
[-] takeWhile.ts [edit]
[-] audit.ts [edit]
[-] reduce.ts [edit]
[-] mapTo.ts [edit]
[-] count.ts [edit]
[-] debounce.ts [edit]
[-] throwIfEmpty.ts [edit]
[-] auditTime.ts [edit]
[-] scan.ts [edit]
[-] switchAll.ts [edit]
[-] map.ts [edit]
[-] bufferCount.ts [edit]
[-] mergeScan.ts [edit]
[-] publish.ts [edit]
[-] min.ts [edit]
[+] ..
[-] publishReplay.ts [edit]
[-] bufferTime.ts [edit]
[-] share.ts [edit]
[-] repeat.ts [edit]
[-] distinct.ts [edit]
[-] concatMapTo.ts [edit]
[-] buffer.ts [edit]
[-] concatMap.ts [edit]
[-] max.ts [edit]
[-] partition.ts [edit]
[-] observeOn.ts [edit]
[-] bufferWhen.ts [edit]
[-] dematerialize.ts [edit]
[-] throttle.ts [edit]
[-] groupBy.ts [edit]
[-] withLatestFrom.ts [edit]
[-] exhaust.ts [edit]
[-] exhaustMap.ts [edit]
[-] retryWhen.ts [edit]
[-] zipAll.ts [edit]
[-] find.ts [edit]
[-] mergeMap.ts [edit]
[-] single.ts [edit]
[-] last.ts [edit]
[-] combineLatest.ts [edit]
[-] publishLast.ts [edit]
[-] pluck.ts [edit]
[-] pairwise.ts [edit]
[-] distinctUntilChanged.ts [edit]
[-] timeInterval.ts [edit]
[-] shareReplay.ts [edit]
[-] skipUntil.ts [edit]
[-] findIndex.ts [edit]
[-] windowToggle.ts [edit]
[-] startWith.ts [edit]
[-] timeoutWith.ts [edit]
[-] concat.ts [edit]
[-] materialize.ts [edit]
[-] timestamp.ts [edit]
[-] onErrorResumeNext.ts [edit]
[-] subscribeOn.ts [edit]
[-] takeUntil.ts [edit]
[-] skipLast.ts [edit]
[-] throttleTime.ts [edit]
[-] mergeMapTo.ts [edit]
[-] multicast.ts [edit]
[-] merge.ts [edit]
[-] takeLast.ts [edit]
[-] delayWhen.ts [edit]
[-] sampleTime.ts [edit]
[-] tap.ts [edit]
[-] take.ts [edit]
[-] sample.ts [edit]
[-] filter.ts [edit]
[-] skip.ts [edit]
[-] expand.ts [edit]
[-] publishBehavior.ts [edit]
[-] sequenceEqual.ts [edit]
[-] ignoreElements.ts [edit]
[-] catchError.ts [edit]
[-] endWith.ts [edit]
[-] refCount.ts [edit]
[-] windowCount.ts [edit]
[-] defaultIfEmpty.ts [edit]
[-] windowTime.ts [edit]
[-] switchMapTo.ts [edit]
[-] switchMap.ts [edit]
[-] delay.ts [edit]
[-] bufferToggle.ts [edit]
[-] repeatWhen.ts [edit]
[-] concatAll.ts [edit]
[-] first.ts [edit]
[-] zip.ts [edit]
[-] elementAt.ts [edit]
[-] skipWhile.ts [edit]
[-] race.ts [edit]
[-] finalize.ts [edit]
[-] combineAll.ts [edit]
[-] distinctUntilKeyChanged.ts [edit]
[-] isEmpty.ts [edit]