| import { Operator } from '../Operator'; |
| import { Observable } from '../Observable'; |
| import { Subscriber } from '../Subscriber'; |
| import { OperatorFunction } from '../types'; |
| |
| /** |
| * 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> |
| * |
| * ![](pairwise.png) |
| * |
| * 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 |
| * On every click (starting from the second), emit the relative distance to the previous click |
| * ```ts |
| * import { fromEvent } from 'rxjs'; |
| * import { pairwise, map } from 'rxjs/operators'; |
| * |
| * const clicks = fromEvent(document, 'click'); |
| * const pairs = clicks.pipe(pairwise()); |
| * const distance = pairs.pipe( |
| * map(pair => { |
| * const x0 = pair[0].clientX; |
| * const y0 = pair[0].clientY; |
| * const x1 = pair[1].clientX; |
| * const 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<T>(): OperatorFunction<T, [T, T]> { |
| return (source: Observable<T>) => source.lift(new PairwiseOperator()); |
| } |
| |
| class PairwiseOperator<T> implements Operator<T, [T, T]> { |
| call(subscriber: Subscriber<[T, T]>, source: any): any { |
| return source.subscribe(new PairwiseSubscriber(subscriber)); |
| } |
| } |
| |
| /** |
| * We need this JSDoc comment for affecting ESDoc. |
| * @ignore |
| * @extends {Ignored} |
| */ |
| class PairwiseSubscriber<T> extends Subscriber<T> { |
| private prev: T; |
| private hasPrev: boolean = false; |
| |
| constructor(destination: Subscriber<[T, T]>) { |
| super(destination); |
| } |
| |
| _next(value: T): void { |
| let pair: [T, T] | undefined; |
| |
| if (this.hasPrev) { |
| pair = [this.prev, value]; |
| } else { |
| this.hasPrev = true; |
| } |
| |
| this.prev = value; |
| |
| if (pair) { |
| this.destination.next(pair); |
| } |
| } |
| } |