88 lines
3.0 KiB
JavaScript
88 lines
3.0 KiB
JavaScript
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import { Subscriber } from '../Subscriber';
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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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* <img src="./img/find.png" width="100%">
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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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*
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* @example <caption>Find and emit the first click that happens on a DIV element</caption>
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* var clicks = Rx.Observable.fromEvent(document, 'click');
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* var result = clicks.find(ev => ev.target.tagName === 'DIV');
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* result.subscribe(x => console.log(x));
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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 {Observable<T>} An Observable of the first item that matches the
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* condition.
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* @method find
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* @owner Observable
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*/
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export function find(predicate, thisArg) {
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if (typeof predicate !== 'function') {
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throw new TypeError('predicate is not a function');
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}
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return (source) => source.lift(new FindValueOperator(predicate, source, false, thisArg));
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}
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export class FindValueOperator {
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constructor(predicate, source, yieldIndex, thisArg) {
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this.predicate = predicate;
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this.source = source;
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this.yieldIndex = yieldIndex;
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this.thisArg = thisArg;
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}
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call(observer, source) {
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return source.subscribe(new FindValueSubscriber(observer, this.predicate, this.source, this.yieldIndex, this.thisArg));
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}
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}
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/**
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* We need this JSDoc comment for affecting ESDoc.
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* @ignore
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* @extends {Ignored}
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*/
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export class FindValueSubscriber extends Subscriber {
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constructor(destination, predicate, source, yieldIndex, thisArg) {
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super(destination);
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this.predicate = predicate;
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this.source = source;
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this.yieldIndex = yieldIndex;
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this.thisArg = thisArg;
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this.index = 0;
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}
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notifyComplete(value) {
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const destination = this.destination;
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destination.next(value);
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destination.complete();
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}
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_next(value) {
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const { predicate, thisArg } = this;
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const index = this.index++;
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try {
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const result = predicate.call(thisArg || this, value, index, this.source);
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if (result) {
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this.notifyComplete(this.yieldIndex ? index : value);
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}
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}
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catch (err) {
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this.destination.error(err);
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}
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}
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_complete() {
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this.notifyComplete(this.yieldIndex ? -1 : undefined);
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}
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}
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//# sourceMappingURL=find.js.map
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