last.js

import { Subscriber } from '../Subscriber';
import { EmptyError } from '../util/EmptyError';
/* tslint:enable:max-line-length */
/**
 * Returns an Observable that emits only the last item emitted by the source Observable.
 * It optionally takes a predicate function as a parameter, in which case, rather than emitting
 * the last item from the source Observable, the resulting Observable will emit the last item
 * from the source Observable that satisfies the predicate.
 *
 * <img src="./img/last.png" width="100%">
 *
 * @throws {EmptyError} Delivers an EmptyError to the Observer's `error`
 * callback if the Observable completes before any `next` notification was sent.
 * @param {function} predicate - The condition any source emitted item has to satisfy.
 * @return {Observable} An Observable that emits only the last item satisfying the given condition
 * from the source, or an NoSuchElementException if no such items are emitted.
 * @throws - Throws if no items that match the predicate are emitted by the source Observable.
 * @method last
 * @owner Observable
 */
export function last(predicate, resultSelector, defaultValue) {
    return (source) => source.lift(new LastOperator(predicate, resultSelector, defaultValue, source));
}
class LastOperator {
    constructor(predicate, resultSelector, defaultValue, source) {
        this.predicate = predicate;
        this.resultSelector = resultSelector;
        this.defaultValue = defaultValue;
        this.source = source;
    }
    call(observer, source) {
        return source.subscribe(new LastSubscriber(observer, this.predicate, this.resultSelector, this.defaultValue, this.source));
    }
}
/**
 * We need this JSDoc comment for affecting ESDoc.
 * @ignore
 * @extends {Ignored}
 */
class LastSubscriber extends Subscriber {
    constructor(destination, predicate, resultSelector, defaultValue, source) {
        super(destination);
        this.predicate = predicate;
        this.resultSelector = resultSelector;
        this.defaultValue = defaultValue;
        this.source = source;
        this.hasValue = false;
        this.index = 0;
        if (typeof defaultValue !== 'undefined') {
            this.lastValue = defaultValue;
            this.hasValue = true;
        }
    }
    _next(value) {
        const index = this.index++;
        if (this.predicate) {
            this._tryPredicate(value, index);
        }
        else {
            if (this.resultSelector) {
                this._tryResultSelector(value, index);
                return;
            }
            this.lastValue = value;
            this.hasValue = true;
        }
    }
    _tryPredicate(value, index) {
        let result;
        try {
            result = this.predicate(value, index, this.source);
        }
        catch (err) {
            this.destination.error(err);
            return;
        }
        if (result) {
            if (this.resultSelector) {
                this._tryResultSelector(value, index);
                return;
            }
            this.lastValue = value;
            this.hasValue = true;
        }
    }
    _tryResultSelector(value, index) {
        let result;
        try {
            result = this.resultSelector(value, index);
        }
        catch (err) {
            this.destination.error(err);
            return;
        }
        this.lastValue = result;
        this.hasValue = true;
    }
    _complete() {
        const destination = this.destination;
        if (this.hasValue) {
            destination.next(this.lastValue);
            destination.complete();
        }
        else {
            destination.error(new EmptyError);
        }
    }
}
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