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