拖拽改变div大小方法

const updateWidth = () => {
      let resize = document.getElementById("datatree");
      let mainForm = document.getElementsByClassName("mainForm");
      resize.onmousedown = function (e) {       
        let startX = e.clientX;
        if(e.target.style.cursor == "e-resize")
      {
       document.onmousemove = function (e) {
        
          let endX = e.clientX;
          let moveLen = endX - startX;
          startX = endX;
          widthData.with += moveLen;
          data.widthTree = widthData.with - 25;
          //e.target.style.cursor = "e-resize"
        };

        document.onmouseup = function (e) {
          // 颜色恢复
          e.target.style.cursor = "auto";
          e.target.style.background = "";
          resize.style.cursor = "auto";
          resize.style.background = "";
          document.getElementById("asideId").style.cursor = "auto";
          document.getElementById("asideId").style.background = "";
          
          for (let index = 0; index < mainForm.length; index++) {
            mainForm[index].style.cursor = "auto";
          mainForm[index].style.background = "";
          }
          
          
          document.onmousemove = null;
          document.onmouseup = null;
           
        };
       
        return false;
      }
        
      };
    };

//在onMounted中实现方法

updateWidth();
      let resize = document.getElementById("asideId");
      let tree = document.getElementById("datatree");
      tree.onmousemove = function (e) {
        var divRect = e.target.getBoundingClientRect();
        var x = e.clientX - divRect.left-20;
        var y = e.clientY - divRect.top;        
        if (e.target.offsetWidth-1<=x||
        e.target.offsetWidth-2<=x||
        e.target.offsetWidth-3<=x||
        e.target.offsetWidth-4<=x||
         e.target.offsetWidth-23<=x||
          e.target.offsetWidth-24<=x||
           e.target.offsetWidth-25<=x
        ) {
    e.target.style.cursor = "e-resize";
  }
        else {
          e.target.style.cursor = "";
        }
      };