将可拖动div的一部分设置为不可拖动

<div class="draggable">
  <div class="non-draggable"></div>
</div>

.draggable {
  position: absolute;
  width: 200px;
  height: 200px;
  background-color: #ccc;
  cursor: move;
}

.non-draggable {
  position: absolute;
  top: 0;
  left: 0;
  width: 50px;
  height: 200px;
  background-color: #f00;
  z-index: 999;
}

document.querySelector('.non-draggable').addEventListener('mousedown', function(event) {
  event.stopPropagation();
});