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  transform translate(10px, 10px)
  transition 0.05s transform ease-out
  width 40px
  height 40px
  background orange
  border 5px solid red
  cursor pointer


                const box = document.getElementById('box')
const mouseDown$ = Rx.Observable.fromEvent(box, 'mousedown')
const mouseMove$ = Rx.Observable.fromEvent(document, 'mousemove')
const mouseUp$ = Rx.Observable.fromEvent(document, 'mouseup')

mouseDown$.map((event) => ({
  pos: getTranslate(box),
.switchMap((initialState) => {
  const initialPos = initialState.pos
  const { clientX, clientY } = initialState.event
  return mouseMove$.map((moveEvent) => ({
    x: moveEvent.clientX - clientX + initialPos.x,
    y: moveEvent.clientY - clientY + initialPos.y,
.subscribe((pos) => {
  setTranslate(box, pos)

function setTranslate (element, pos) { = `translate(${pos.x}px, ${pos.y}px)`

function getTranslate (element) {
  const style = getComputedStyle(element)
  const regExp = /matrix\((\d+,\s){4}(\d+),\s(\d+)/i
  const result = style.transform.match(regExp)
  if (result) {
    return {
      x: parseInt(result[2], 10),
      y: parseInt(result[3], 10)
  } else {
    return {
      x: 0,
      y: 0