var curYPos = 0,
    curXPos = 0,
    curDown = false;

window.addEventListener('mousemove', function(e){ 
  if(curDown === true){
    window.scrollTo(document.body.scrollLeft + (curXPos - e.pageX), document.body.scrollTop + (curYPos - e.pageY));
    // window.scrollTo(document.body.scrollLeft + (curXPos - e.pageX), document.body.scrollTop);
  }
});

window.addEventListener('mousedown', function(e){ curDown = true; curYPos = e.pageY; curXPos = e.pageX; });
window.addEventListener('mouseup', function(e){ curDown = false; });