передвигать элемент при зажатие мыши

var app = document.getElementById('app');

var left = 0;

var step = 10;

app.addEventListener('mousedown', function(e){
  window.addEventListener('mousemove', mouseMove);
  window.addEventListener('mouseup', mouseUp);
  console.log('down');
  function mouseMove(e){
    left += step;
    app.style.left = left + 'px';
    console.log('move');
  }
  function mouseUp(e){
    window.removeEventListener('mousemove', mouseMove);
    window.removeEventListener('mouseup', mouseUp);
    console.log('up');
  }
})