65 lines
2.0 KiB
JavaScript
65 lines
2.0 KiB
JavaScript
import { Subscriber } from '../Subscriber';
|
|
/**
|
|
* Groups pairs of consecutive emissions together and emits them as an array of
|
|
* two values.
|
|
*
|
|
* <span class="informal">Puts the current value and previous value together as
|
|
* an array, and emits that.</span>
|
|
*
|
|
* <img src="./img/pairwise.png" width="100%">
|
|
*
|
|
* The Nth emission from the source Observable will cause the output Observable
|
|
* to emit an array [(N-1)th, Nth] of the previous and the current value, as a
|
|
* pair. For this reason, `pairwise` emits on the second and subsequent
|
|
* emissions from the source Observable, but not on the first emission, because
|
|
* there is no previous value in that case.
|
|
*
|
|
* @example <caption>On every click (starting from the second), emit the relative distance to the previous click</caption>
|
|
* var clicks = Rx.Observable.fromEvent(document, 'click');
|
|
* var pairs = clicks.pairwise();
|
|
* var distance = pairs.map(pair => {
|
|
* var x0 = pair[0].clientX;
|
|
* var y0 = pair[0].clientY;
|
|
* var x1 = pair[1].clientX;
|
|
* var y1 = pair[1].clientY;
|
|
* return Math.sqrt(Math.pow(x0 - x1, 2) + Math.pow(y0 - y1, 2));
|
|
* });
|
|
* distance.subscribe(x => console.log(x));
|
|
*
|
|
* @see {@link buffer}
|
|
* @see {@link bufferCount}
|
|
*
|
|
* @return {Observable<Array<T>>} An Observable of pairs (as arrays) of
|
|
* consecutive values from the source Observable.
|
|
* @method pairwise
|
|
* @owner Observable
|
|
*/
|
|
export function pairwise() {
|
|
return (source) => source.lift(new PairwiseOperator());
|
|
}
|
|
class PairwiseOperator {
|
|
call(subscriber, source) {
|
|
return source.subscribe(new PairwiseSubscriber(subscriber));
|
|
}
|
|
}
|
|
/**
|
|
* We need this JSDoc comment for affecting ESDoc.
|
|
* @ignore
|
|
* @extends {Ignored}
|
|
*/
|
|
class PairwiseSubscriber extends Subscriber {
|
|
constructor(destination) {
|
|
super(destination);
|
|
this.hasPrev = false;
|
|
}
|
|
_next(value) {
|
|
if (this.hasPrev) {
|
|
this.destination.next([this.prev, value]);
|
|
}
|
|
else {
|
|
this.hasPrev = true;
|
|
}
|
|
this.prev = value;
|
|
}
|
|
}
|
|
//# sourceMappingURL=pairwise.js.map
|