48 lines
1.9 KiB
JavaScript
48 lines
1.9 KiB
JavaScript
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/** PURE_IMPORTS_START .._operators_scan PURE_IMPORTS_END */
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import { scan as higherOrderScan } from '../operators/scan';
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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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if (arguments.length >= 2) {
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return higherOrderScan(accumulator, seed)(this);
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}
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return higherOrderScan(accumulator)(this);
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}
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//# sourceMappingURL=scan.js.map
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