@reactivex/rxjs/dist/amd/operator/scan.js

Reactive Extensions for modern JavaScript

var __extends = (this && this.__extends) || function (d, b) {
    for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
    function __() { this.constructor = d; }
    d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
define(["require", "exports", '../Subscriber'], function (require, exports, Subscriber_1) {
    "use strict";
    /**
     * Applies an accumulator function over the source Observable, and returns each
     * intermediate result, with an optional seed value.
     *
     * <span class="informal">It's like {@link reduce}, but emits the current
     * accumulation whenever the source emits a value.</span>
     *
     * <img src="./img/scan.png" width="100%">
     *
     * Combines together all values emitted on the source, using an accumulator
     * function that knows how to join a new source value into the accumulation from
     * the past. Is similar to {@link reduce}, but emits the intermediate
     * accumulations.
     *
     * Returns an Observable that applies a specified `accumulator` function to each
     * item emitted by the source Observable. If a `seed` value is specified, then
     * that value will be used as the initial value for the accumulator. If no seed
     * value is specified, the first item of the source is used as the seed.
     *
     * @example <caption>Count the number of click events</caption>
     * var clicks = Rx.Observable.fromEvent(document, 'click');
     * var ones = clicks.mapTo(1);
     * var seed = 0;
     * var count = ones.scan((acc, one) => acc + one, seed);
     * count.subscribe(x => console.log(x));
     *
     * @see {@link expand}
     * @see {@link mergeScan}
     * @see {@link reduce}
     *
     * @param {function(acc: R, value: T, index: number): R} accumulator
     * The accumulator function called on each source value.
     * @param {T|R} [seed] The initial accumulation value.
     * @return {Observable<R>} An observable of the accumulated values.
     * @method scan
     * @owner Observable
     */
    function scan(accumulator, seed) {
        return this.lift(new ScanOperator(accumulator, seed));
    }
    exports.scan = scan;
    var ScanOperator = (function () {
        function ScanOperator(accumulator, seed) {
            this.accumulator = accumulator;
            this.seed = seed;
        }
        ScanOperator.prototype.call = function (subscriber, source) {
            return source._subscribe(new ScanSubscriber(subscriber, this.accumulator, this.seed));
        };
        return ScanOperator;
    }());
    /**
     * We need this JSDoc comment for affecting ESDoc.
     * @ignore
     * @extends {Ignored}
     */
    var ScanSubscriber = (function (_super) {
        __extends(ScanSubscriber, _super);
        function ScanSubscriber(destination, accumulator, seed) {
            _super.call(this, destination);
            this.accumulator = accumulator;
            this.index = 0;
            this.accumulatorSet = false;
            this.seed = seed;
            this.accumulatorSet = typeof seed !== 'undefined';
        }
        Object.defineProperty(ScanSubscriber.prototype, "seed", {
            get: function () {
                return this._seed;
            },
            set: function (value) {
                this.accumulatorSet = true;
                this._seed = value;
            },
            enumerable: true,
            configurable: true
        });
        ScanSubscriber.prototype._next = function (value) {
            if (!this.accumulatorSet) {
                this.seed = value;
                this.destination.next(value);
            }
            else {
                return this._tryNext(value);
            }
        };
        ScanSubscriber.prototype._tryNext = function (value) {
            var index = this.index++;
            var result;
            try {
                result = this.accumulator(this.seed, value, index);
            }
            catch (err) {
                this.destination.error(err);
            }
            this.seed = result;
            this.destination.next(result);
        };
        return ScanSubscriber;
    }(Subscriber_1.Subscriber));
});
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