rxjs drag and drop with touch support

index.js

var mousemove = Rx.Observable.merge(
            Rx.Observable.fromEvent(document, 'mousemove')
                .map((e) => { e.preventDefault(); return e; }),
            Rx.Observable.fromEvent(document, 'touchmove'))
                .map((e) => e.touches[0]),
        mouseup = Rx.Observable.merge(
            Rx.Observable.fromEvent(dragTarget, 'mouseup'),
            Rx.Observable.fromEvent(dragTarget, 'touchend')),
        mousedown = Rx.Observable.merge(
            Rx.Observable.fromEvent(dragTarget, 'mousedown'),
            Rx.Observable.fromEvent(dragTarget, 'touchstart')
                .map((e) => {
                    var rect = e.target.getBoundingClientRect();
                    e.offsetX = e.touches[0].pageX - rect.left;
                    e.offsetY = e.touches[0].pageY - rect.top;
                    return e;
                }));

mousedown
    .flatMap((start) => mousemove
        .map((mm) =>({
            left: mm.clientX - start.offsetX,
            top: mm.clientY - start.offsetY
        }))
        .takeUntil(mouseup))
    .subscribe(function (pos) {
        dragTarget.style.top = pos.top + 'px';
        dragTarget.style.left = pos.left + 'px';
    });