let button = document.querySelector('.button');

​

let mouseDownStream = Rx.Observable.fromEvent(button, 'mousedown');

let mouseUpStream = Rx.Observable.fromEvent(button, 'mouseup');

​

let dragStream = mouseDownStream

  .flatMap((event) => {

    return Rx.Observable

      .return(event)

      .delay(250)

      .takeUntil(mouseUpStream)

  });

​

let dropStream = mouseUpStream

  .flatMap((event) => {

    return Rx.Observable

      .return(event)

      .skipUntil(dragStream)

  });

​

dragStream.subscribe(event => console.log('start drag'));

dropStream.subscribe(event => console.log('stop drag'));