106 lines
3.5 KiB
JavaScript
106 lines
3.5 KiB
JavaScript
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import { Subscriber } from '../Subscriber';
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/* tslint:enable:max-line-length */
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/**
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* Applies an accumulator function over the source Observable, and returns each
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* intermediate result, with an optional seed value.
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*
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* <span class="informal">It's like {@link reduce}, but emits the current
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* accumulation whenever the source emits a value.</span>
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*
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* <img src="./img/scan.png" width="100%">
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*
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* Combines together all values emitted on the source, using an accumulator
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* function that knows how to join a new source value into the accumulation from
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* the past. Is similar to {@link reduce}, but emits the intermediate
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* accumulations.
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*
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* Returns an Observable that applies a specified `accumulator` function to each
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* item emitted by the source Observable. If a `seed` value is specified, then
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* that value will be used as the initial value for the accumulator. If no seed
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* value is specified, the first item of the source is used as the seed.
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*
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* @example <caption>Count the number of click events</caption>
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* var clicks = Rx.Observable.fromEvent(document, 'click');
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* var ones = clicks.mapTo(1);
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* var seed = 0;
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* var count = ones.scan((acc, one) => acc + one, seed);
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* count.subscribe(x => console.log(x));
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*
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* @see {@link expand}
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* @see {@link mergeScan}
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* @see {@link reduce}
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*
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* @param {function(acc: R, value: T, index: number): R} accumulator
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* The accumulator function called on each source value.
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* @param {T|R} [seed] The initial accumulation value.
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* @return {Observable<R>} An observable of the accumulated values.
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* @method scan
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* @owner Observable
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*/
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export function scan(accumulator, seed) {
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let hasSeed = false;
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// providing a seed of `undefined` *should* be valid and trigger
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// hasSeed! so don't use `seed !== undefined` checks!
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// For this reason, we have to check it here at the original call site
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// otherwise inside Operator/Subscriber we won't know if `undefined`
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// means they didn't provide anything or if they literally provided `undefined`
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if (arguments.length >= 2) {
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hasSeed = true;
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}
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return function scanOperatorFunction(source) {
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return source.lift(new ScanOperator(accumulator, seed, hasSeed));
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};
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}
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class ScanOperator {
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constructor(accumulator, seed, hasSeed = false) {
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this.accumulator = accumulator;
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this.seed = seed;
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this.hasSeed = hasSeed;
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}
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call(subscriber, source) {
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return source.subscribe(new ScanSubscriber(subscriber, this.accumulator, this.seed, this.hasSeed));
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}
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}
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/**
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* We need this JSDoc comment for affecting ESDoc.
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* @ignore
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* @extends {Ignored}
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*/
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class ScanSubscriber extends Subscriber {
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constructor(destination, accumulator, _seed, hasSeed) {
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super(destination);
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this.accumulator = accumulator;
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this._seed = _seed;
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this.hasSeed = hasSeed;
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this.index = 0;
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}
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get seed() {
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return this._seed;
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}
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set seed(value) {
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this.hasSeed = true;
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this._seed = value;
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}
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_next(value) {
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if (!this.hasSeed) {
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this.seed = value;
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this.destination.next(value);
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}
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else {
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return this._tryNext(value);
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}
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}
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_tryNext(value) {
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const index = this.index++;
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let result;
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try {
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result = this.accumulator(this.seed, value, index);
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}
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catch (err) {
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this.destination.error(err);
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}
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this.seed = result;
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this.destination.next(result);
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}
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}
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//# sourceMappingURL=scan.js.map
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