vue自定义指令之面板拖拽的实现

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

directives: {
  drag: {
   // 使用bind会有可能没有渲染完成
   inserted: function(el, binding, vnode) {
    const _el = el; //获取当前元素
    const ref = vnode.context.$refs[binding.value]; // 判断基于移动的是哪一个盒子
    const masterNode = ref ? ref : document; // 用于绑定事件
    const masterBody = ref ? ref : document.body; // 用于获取高和宽
    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 => {
     //算出鼠标相对元素的位置，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 => {
      //用鼠标的位置减去鼠标相对元素的位置，得到元素的位置
      let left = e.clientX - disX;
      let top = e.clientY - disY;
      // 绑定的值不能滑出基于盒子的范围
      left < 0 && (left = 0);
      left > (maxWidth - elWidth - mgl) && (left = maxWidth - elWidth - mgl);
      top < 0 && (top = 0);
      top > (maxHeight - elHeight - mgt) && (top = maxHeight - elHeight - mgt);
      //绑定元素位置到positionX和positionY上面
      positionX = top;
      positionY = left;
      
      //移动当前元素
      _el.style.left = left + "px";
      _el.style.top = top + "px";
     };
     // 这里是鼠标超出基于盒子范围之后再松开，会监听不到
     document.onmouseup = e => {
      masterNode.onmousemove = null;
      document.onmouseup = null;
     };
    };
   }
  }
 }