//自定义指令
      directives: {
        drag: {
          // 指令的定义
          bind: function(el) {
            let oDiv = el;  // 获取当前元素
            oDiv.onmousedown = (e) => {
              // 算出鼠标相对元素的位置
              let disX = e.clientX - oDiv.offsetLeft;
              let disY = e.clientY - oDiv.offsetTop;
              console.log("本身的宽高",oDiv.clientHeight);

              document.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;

                if (left <= 0) {
                  left = 0;
                } else if (left >= document.documentElement.clientWidth - oDiv.clientWidth){
                  //document.documentElement.clientWidth 屏幕的可视宽度
                  left = document.documentElement.clientWidth - oDiv.clientWidth
                }
                if (top <= 0) {
                  top = 0;
                } else if (top >= document.documentElement.clientHeight - oDiv.clientHeight){
                  // document.documentElement.clientHeight 屏幕的可视高度
                  top = document.documentElement.clientHeight - oDiv.clientHeight

                }

                oDiv.style.left = left + 'px';
                oDiv.style.top = top + 'px';

              };

              document.onmouseup = (e) => {
                document.onmousemove = null;
                document.onmouseup = null;
              }
            }
          }
        }
      },

<div  v-drag ></div>//使用v-drag