<div v-drag="'refName'"></div>

directives: {
  drag: {
   // 使用bind會有可能沒有渲染完成
   inserted: function(el, binding, vnode) {
    const _el = el; //獲取當(dāng)前元素
    const ref = vnode.context.$refs[binding.value]; // 判斷基于移動的是哪一個盒子
    const masterNode = ref ? ref : document; // 用于綁定事件
    const masterBody = ref ? ref : document.body; // 用于獲取高和寬
    const mgl = _el.offsetLeft;
    const mgt = _el.offsetTop;
    const maxWidth = masterBody.clientWidth;
    const maxHeight = masterBody.clientHeight;
    const elWidth = _el.clientWidth;
    const elHeight = _el.clientHeight;
    let positionX = 0,
     positionY = 0;
    _el.onmousedown = e => {
     //算出鼠標(biāo)相對元素的位置，加上的值是margin的值
     let disX = e.clientX - _el.offsetLeft + mgl; 
     let disY = e.clientY - _el.offsetTop + mgt;
     masterNode.onmousemove = e => {
      //用鼠標(biāo)的位置減去鼠標(biāo)相對元素的位置，得到元素的位置
      let left = e.clientX - disX;
      let top = e.clientY - disY;
      // 綁定的值不能滑出基于盒子的范圍
      left < 0 && (left = 0);
      left > (maxWidth - elWidth - mgl) && (left = maxWidth - elWidth - mgl);
      top < 0 && (top = 0);
      top > (maxHeight - elHeight - mgt) && (top = maxHeight - elHeight - mgt);
      //綁定元素位置到positionX和positionY上面
      positionX = top;
      positionY = left;
      
      //移動當(dāng)前元素
      _el.style.left = left + "px";
      _el.style.top = top + "px";
     };
     // 這里是鼠標(biāo)超出基于盒子范圍之后再松開，會監(jiān)聽不到
     document.onmouseup = e => {
      masterNode.onmousemove = null;
      document.onmouseup = null;
     };
    };
   }
  }
 }