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