work.suroh.tk/node_modules/rxjs/_esm2015/operators/find.js

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2019-12-02 12:22:45 +00:00
import { Subscriber } from '../Subscriber';
/**
* 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>
*
* <img src="./img/find.png" width="100%">
*
* `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.
*
* @example <caption>Find and emit the first click that happens on a DIV element</caption>
* var clicks = Rx.Observable.fromEvent(document, 'click');
* var result = clicks.find(ev => ev.target.tagName === 'DIV');
* result.subscribe(x => console.log(x));
*
* @see {@link filter}
* @see {@link first}
* @see {@link findIndex}
* @see {@link take}
*
* @param {function(value: T, index: number, source: Observable<T>): boolean} predicate
* A function called with each item to test for condition matching.
* @param {any} [thisArg] An optional argument to determine the value of `this`
* in the `predicate` function.
* @return {Observable<T>} An Observable of the first item that matches the
* condition.
* @method find
* @owner Observable
*/
export function find(predicate, thisArg) {
if (typeof predicate !== 'function') {
throw new TypeError('predicate is not a function');
}
return (source) => source.lift(new FindValueOperator(predicate, source, false, thisArg));
}
export class FindValueOperator {
constructor(predicate, source, yieldIndex, thisArg) {
this.predicate = predicate;
this.source = source;
this.yieldIndex = yieldIndex;
this.thisArg = thisArg;
}
call(observer, source) {
return source.subscribe(new FindValueSubscriber(observer, this.predicate, this.source, this.yieldIndex, this.thisArg));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
export class FindValueSubscriber extends Subscriber {
constructor(destination, predicate, source, yieldIndex, thisArg) {
super(destination);
this.predicate = predicate;
this.source = source;
this.yieldIndex = yieldIndex;
this.thisArg = thisArg;
this.index = 0;
}
notifyComplete(value) {
const destination = this.destination;
destination.next(value);
destination.complete();
}
_next(value) {
const { predicate, thisArg } = this;
const index = this.index++;
try {
const result = predicate.call(thisArg || this, value, index, this.source);
if (result) {
this.notifyComplete(this.yieldIndex ? index : value);
}
}
catch (err) {
this.destination.error(err);
}
}
_complete() {
this.notifyComplete(this.yieldIndex ? -1 : undefined);
}
}
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