Перемещение фона мышкой

const d = document.querySelector('.bg'); 
 
let state = 'off'; 
let initialMousePos, initialPos = {x: 0, y: 0}; 
 
d.addEventListener('mousedown', e => { 
  state = 'on'; 
  initialMousePos = {x: e.clientX, y: e.clientY}; 
}); 
document.addEventListener('mouseup', e => { 
  if (state !== 'on') return; 
  state = 'off'; 
  initialPos.x = initialPos.x + e.clientX - initialMousePos.x; 
  initialPos.y = initialPos.y + e.clientY - initialMousePos.y; 
}); 
 
d.addEventListener('mousemove', e => { 
  if (state !== 'on') return; 
  d.style.backgroundPositionX = (initialPos.x + e.clientX - initialMousePos.x) + 'px'; 
  d.style.backgroundPositionY = (initialPos.y + e.clientY - initialMousePos.y) + 'px'; 
});

.bg { 
  width: 100px; 
  height: 100px; 
  background-image: url(http://placekitten.com/200/300); 
}

<div class=bg></div>