work.suroh.tk/node_modules/rxjs/_esm2015/operators/scan.js

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);
}
}
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