import { Observable } from '../Observable';
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import { Subscriber } from '../Subscriber';
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import { OperatorFunction, TruthyTypesOf } from '../types';
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import { operate } from '../util/lift';
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import { createOperatorSubscriber } from './OperatorSubscriber';
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export function find<T>(predicate: BooleanConstructor): OperatorFunction<T, TruthyTypesOf<T>>;
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/** @deprecated Use a closure instead of a `thisArg`. Signatures accepting a `thisArg` will be removed in v8. */
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export function find<T, S extends T, A>(
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predicate: (this: A, value: T, index: number, source: Observable<T>) => value is S,
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thisArg: A
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): OperatorFunction<T, S | undefined>;
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export function find<T, S extends T>(
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predicate: (value: T, index: number, source: Observable<T>) => value is S
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): OperatorFunction<T, S | undefined>;
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/** @deprecated Use a closure instead of a `thisArg`. Signatures accepting a `thisArg` will be removed in v8. */
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export function find<T, A>(
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predicate: (this: A, value: T, index: number, source: Observable<T>) => boolean,
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thisArg: A
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): OperatorFunction<T, T | undefined>;
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export function find<T>(predicate: (value: T, index: number, source: Observable<T>) => boolean): OperatorFunction<T, T | undefined>;
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/**
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* Emits only the first value emitted by the source Observable that meets some
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* condition.
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*
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* <span class="informal">Finds the first value that passes some test and emits
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* that.</span>
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*
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* 
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*
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* `find` searches for the first item in the source Observable that matches the
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* specified condition embodied by the `predicate`, and returns the first
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* occurrence in the source. Unlike {@link first}, the `predicate` is required
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* in `find`, and does not emit an error if a valid value is not found
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* (emits `undefined` instead).
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*
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* ## Example
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*
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* Find and emit the first click that happens on a DIV element
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*
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* ```ts
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* import { fromEvent, find } from 'rxjs';
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*
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* const div = document.createElement('div');
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* div.style.cssText = 'width: 200px; height: 200px; background: #09c;';
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* document.body.appendChild(div);
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*
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* const clicks = fromEvent(document, 'click');
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* const result = clicks.pipe(find(ev => (<HTMLElement>ev.target).tagName === 'DIV'));
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* result.subscribe(x => console.log(x));
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* ```
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*
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* @see {@link filter}
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* @see {@link first}
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* @see {@link findIndex}
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* @see {@link take}
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*
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* @param {function(value: T, index: number, source: Observable<T>): boolean} predicate
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* A function called with each item to test for condition matching.
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* @param {any} [thisArg] An optional argument to determine the value of `this`
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* in the `predicate` function.
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* @return A function that returns an Observable that emits the first item that
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* matches the condition.
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*/
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export function find<T>(
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predicate: (value: T, index: number, source: Observable<T>) => boolean,
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thisArg?: any
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): OperatorFunction<T, T | undefined> {
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return operate(createFind(predicate, thisArg, 'value'));
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}
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export function createFind<T>(
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predicate: (value: T, index: number, source: Observable<T>) => boolean,
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thisArg: any,
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emit: 'value' | 'index'
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) {
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const findIndex = emit === 'index';
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return (source: Observable<T>, subscriber: Subscriber<any>) => {
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let index = 0;
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source.subscribe(
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createOperatorSubscriber(
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subscriber,
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(value) => {
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const i = index++;
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if (predicate.call(thisArg, value, i, source)) {
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subscriber.next(findIndex ? i : value);
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subscriber.complete();
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}
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},
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() => {
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subscriber.next(findIndex ? -1 : undefined);
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subscriber.complete();
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}
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)
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);
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};
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}
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