VUE 拖拽框

 <div @mousedown="mousedown" id="dragbox" class="dragbox">
 </div>

    mousedown(event) {
      this.selectElement = document.getElementById("dragbox");
      var div1 = this.selectElement;
      this.selectElement.style.cursor = "move";
      this.isDowm = true;
      var distanceX = event.clientX - this.selectElement.offsetLeft;
      var distanceY = event.clientY - this.selectElement.offsetTop;
      document.onmousemove = function(ev) {
        var oevent = ev || event;
        div1.style.left = oevent.clientX - distanceX + "px";
        div1.style.top = oevent.clientY - distanceY + "px";
      };
      document.onmouseup = function() {
        document.onmousemove = null;
        document.onmouseup = null;
        div1.style.cursor = "default";
      };
    },