106 lines
3.5 KiB
JavaScript
106 lines
3.5 KiB
JavaScript
import { Subscriber } from '../Subscriber';
|
|
/* 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) {
|
|
let hasSeed = false;
|
|
// providing a seed of `undefined` *should* be valid and trigger
|
|
// hasSeed! so don't use `seed !== undefined` checks!
|
|
// For this reason, we have to check it here at the original call site
|
|
// otherwise inside Operator/Subscriber we won't know if `undefined`
|
|
// means they didn't provide anything or if they literally provided `undefined`
|
|
if (arguments.length >= 2) {
|
|
hasSeed = true;
|
|
}
|
|
return function scanOperatorFunction(source) {
|
|
return source.lift(new ScanOperator(accumulator, seed, hasSeed));
|
|
};
|
|
}
|
|
class ScanOperator {
|
|
constructor(accumulator, seed, hasSeed = false) {
|
|
this.accumulator = accumulator;
|
|
this.seed = seed;
|
|
this.hasSeed = hasSeed;
|
|
}
|
|
call(subscriber, source) {
|
|
return source.subscribe(new ScanSubscriber(subscriber, this.accumulator, this.seed, this.hasSeed));
|
|
}
|
|
}
|
|
/**
|
|
* We need this JSDoc comment for affecting ESDoc.
|
|
* @ignore
|
|
* @extends {Ignored}
|
|
*/
|
|
class ScanSubscriber extends Subscriber {
|
|
constructor(destination, accumulator, _seed, hasSeed) {
|
|
super(destination);
|
|
this.accumulator = accumulator;
|
|
this._seed = _seed;
|
|
this.hasSeed = hasSeed;
|
|
this.index = 0;
|
|
}
|
|
get seed() {
|
|
return this._seed;
|
|
}
|
|
set seed(value) {
|
|
this.hasSeed = true;
|
|
this._seed = value;
|
|
}
|
|
_next(value) {
|
|
if (!this.hasSeed) {
|
|
this.seed = value;
|
|
this.destination.next(value);
|
|
}
|
|
else {
|
|
return this._tryNext(value);
|
|
}
|
|
}
|
|
_tryNext(value) {
|
|
const index = this.index++;
|
|
let result;
|
|
try {
|
|
result = this.accumulator(this.seed, value, index);
|
|
}
|
|
catch (err) {
|
|
this.destination.error(err);
|
|
}
|
|
this.seed = result;
|
|
this.destination.next(result);
|
|
}
|
|
}
|
|
//# sourceMappingURL=scan.js.map
|