code: function init(el, binding) {
    const $el = el;
    const $binding = binding;
  
    // 处理绑定的值
    $el.dropConfig = dealWithBindingValue($binding);
    $el.dragList = getList($el);
    $el.dragEndCallback = dragEndCallback($el);
    // 绑定事件
    addEvents($el, $binding);
  }
docs: 初始化指令