88 lines
3.0 KiB
JavaScript
88 lines
3.0 KiB
JavaScript
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);
|
|
}
|
|
}
|
|
//# sourceMappingURL=find.js.map
|