es6/operators/distinct.js

import { OuterSubscriber } from '../OuterSubscriber';
import { subscribeToResult } from '../util/subscribeToResult';
import { Set } from '../util/Set';
/**
 * Returns an Observable that emits all items emitted by the source Observable that are distinct by comparison from previous items.
 *
 * If a keySelector function is provided, then it will project each value from the source observable into a new value that it will
 * check for equality with previously projected values. If a keySelector function is not provided, it will use each value from the
 * source observable directly with an equality check against previous values.
 *
 * In JavaScript runtimes that support `Set`, this operator will use a `Set` to improve performance of the distinct value checking.
 *
 * In other runtimes, this operator will use a minimal implementation of `Set` that relies on an `Array` and `indexOf` under the
 * hood, so performance will degrade as more values are checked for distinction. Even in newer browsers, a long-running `distinct`
 * use might result in memory leaks. To help alleviate this in some scenarios, an optional `flushes` parameter is also provided so
 * that the internal `Set` can be "flushed", basically clearing it of values.
 *
 * @example <caption>A simple example with numbers</caption>
 * Observable.of(1, 1, 2, 2, 2, 1, 2, 3, 4, 3, 2, 1)
 *   .distinct()
 *   .subscribe(x => console.log(x)); // 1, 2, 3, 4
 *
 * @example <caption>An example using a keySelector function</caption>
 * interface Person {
 *    age: number,
 *    name: string
 * }
 *
 * Observable.of<Person>(
 *     { age: 4, name: 'Foo'},
 *     { age: 7, name: 'Bar'},
 *     { age: 5, name: 'Foo'})
 *     .distinct((p: Person) => p.name)
 *     .subscribe(x => console.log(x));
 *
 * // displays:
 * // { age: 4, name: 'Foo' }
 * // { age: 7, name: 'Bar' }
 *
 * @see {@link distinctUntilChanged}
 * @see {@link distinctUntilKeyChanged}
 *
 * @param {function} [keySelector] Optional function to select which value you want to check as distinct.
 * @param {Observable} [flushes] Optional Observable for flushing the internal HashSet of the operator.
 * @return {Observable} An Observable that emits items from the source Observable with distinct values.
 * @method distinct
 * @owner Observable
 */
export function distinct(keySelector, flushes) {
    return (source) => source.lift(new DistinctOperator(keySelector, flushes));
}
class DistinctOperator {
    constructor(keySelector, flushes) {
        this.keySelector = keySelector;
        this.flushes = flushes;
    }
    call(subscriber, source) {
        return source.subscribe(new DistinctSubscriber(subscriber, this.keySelector, this.flushes));
    }
}
/**
 * We need this JSDoc comment for affecting ESDoc.
 * @ignore
 * @extends {Ignored}
 */
export class DistinctSubscriber extends OuterSubscriber {
    constructor(destination, keySelector, flushes) {
        super(destination);
        this.keySelector = keySelector;
        this.values = new Set();
        if (flushes) {
            this.add(subscribeToResult(this, flushes));
        }
    }
    notifyNext(outerValue, innerValue, outerIndex, innerIndex, innerSub) {
        this.values.clear();
    }
    notifyError(error, innerSub) {
        this._error(error);
    }
    _next(value) {
        if (this.keySelector) {
            this._useKeySelector(value);
        }
        else {
            this._finalizeNext(value, value);
        }
    }
    _useKeySelector(value) {
        let key;
        const { destination } = this;
        try {
            key = this.keySelector(value);
        }
        catch (err) {
            destination.error(err);
            return;
        }
        this._finalizeNext(key, value);
    }
    _finalizeNext(key, value) {
        const { values } = this;
        if (!values.has(key)) {
            values.add(key);
            this.destination.next(value);
        }
    }
}
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