Move down the array change its value

 <div id="app">
     <el-row>
       <el-button type="info" @click="getInfoUP">向上</el-button>
       <el-button type="warning" @click="getDown">向下</el-button> 
     </el-row>
     <div>
        <div @click="coverHandler(index, item)" class="div-demo" :class="{active:cur==index}" v-for="(item,index) in menuData" :key="index">{{ item.con }}</div>
     </div>
     
   </div>

  <script>
    new Vue({
      el: '#app',
        data() {
          return {
            coverNum:0,
            cur:0,
            menuData:[
              {id:"1", con:"1111",sortNum:1},
              {id:"2", con:"2222",sortNum:2},
              {id:"3", con:"333",sortNum:3},
              {id:"4", con:"444",sortNum:4},
              {id:"5", con:"5555",sortNum:5}
            ],
            contmenutemporarymess:{},   
         };
        },
        
        
        methods:{
            // 向上
            getInfoUP(){
                console.log("数据",this.coverNum);
                if(this.coverNum == 0){//第一个节点不移动
                    alert("第一个节点不能移动")
                    return;
                }else{
                    let curObj = this.menuData[this.coverNum];//当前位置对象
                    let preObj = this.menuData[this.coverNum-1];//上一个位置对象
                    
                    // 更改sortNum值
                    let newpreObj=preObj;
                    preObj.sortNum=curObj.sortNum;
                    curObj.sortNum=newpreObj.sortNum-1;  //之所以要减1,是因为它始终输出的是一个固定的值
                   
                    //替换内容
                    this.menuData.splice(this.coverNum,1,preObj);//上一个节点移动到当前节点
                    this.menuData.splice(this.coverNum-1,1,curObj);//当前节点往上移动
                
                    this.coverNum=this.coverNum-1   

                }    
            },
            
            getDown(){
                console.log("数据",this.coverNum);
                if( this.coverNum == this.menuData.length-1){//最后节点不移动
                    }else{
                        let curObj = this.menuData[this.coverNum];//当前位置对象
                        let downObj = this.menuData[this.coverNum+1];//下一个位置对象
                        
                        // 更改sortNum值
                        let  newdown=downObj;
                        downObj.sortNum=curObj.sortNum;
                        curObj.sortNum=newdown.sortNum+1;
                        
                        //替换内容  
                        console.log("当前",curObj ,"下一个", downObj)
                        this.menuData.splice(this.coverNum,1,downObj);//下一个节点移动到当前节点
                        this.menuData.splice(this.coverNum+1,1,curObj);//当前节点往下移动
                        this.coverNum=this.coverNum+1
                }

            },
            
            coverHandler(mess,con){
                this.cur=mess;
                this.coverNum=mess;
                this.contmenutemporarymess=con;
                console.log("注册 ",this.coverNum,"类容",con)
            }
        }
    })
  </script>