source: trip-planner-front/node_modules/rxjs/internal/operators/pairwise.d.ts

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1import { OperatorFunction } from '../types';
2/**
3 * Groups pairs of consecutive emissions together and emits them as an array of
4 * two values.
5 *
6 * <span class="informal">Puts the current value and previous value together as
7 * an array, and emits that.</span>
8 *
9 * ![](pairwise.png)
10 *
11 * The Nth emission from the source Observable will cause the output Observable
12 * to emit an array [(N-1)th, Nth] of the previous and the current value, as a
13 * pair. For this reason, `pairwise` emits on the second and subsequent
14 * emissions from the source Observable, but not on the first emission, because
15 * there is no previous value in that case.
16 *
17 * ## Example
18 * On every click (starting from the second), emit the relative distance to the previous click
19 * ```ts
20 * import { fromEvent } from 'rxjs';
21 * import { pairwise, map } from 'rxjs/operators';
22 *
23 * const clicks = fromEvent(document, 'click');
24 * const pairs = clicks.pipe(pairwise());
25 * const distance = pairs.pipe(
26 * map(pair => {
27 * const x0 = pair[0].clientX;
28 * const y0 = pair[0].clientY;
29 * const x1 = pair[1].clientX;
30 * const y1 = pair[1].clientY;
31 * return Math.sqrt(Math.pow(x0 - x1, 2) + Math.pow(y0 - y1, 2));
32 * }),
33 * );
34 * distance.subscribe(x => console.log(x));
35 * ```
36 *
37 * @see {@link buffer}
38 * @see {@link bufferCount}
39 *
40 * @return {Observable<Array<T>>} An Observable of pairs (as arrays) of
41 * consecutive values from the source Observable.
42 * @method pairwise
43 * @owner Observable
44 */
45export declare function pairwise<T>(): OperatorFunction<T, [T, T]>;
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