mousedrag-4.js

import { paint } from './canvas.js';
const { fromEvent } = Rx.Observable;
const { skipUntil, takeUntil } = Rx.operators;

const move$ = fromEvent(document, 'mousemove');
const down$ = fromEvent(document, 'mousedown')
const up$ = fromEvent(document, 'mouseup')

const paints$ = move$.pipe(
  skipUntil(down$),
  takeUntil(up$)
);

paints$.subscribe(paint);