el-table中span-method合并单元格报错

开发过程中用到了elementUI中table组件，合并单元格时遇到了You may have an infinite update loop in a component render function.
经排查发现时由于方法中 在data 中定义了变量firstName 并使用与改变了该变量的原因
尽量将变量定义到方法内

objectSpanMethod({ row, column, rowIndex, columnIndex }) {
      const length = this.list.filter(item => (item.firstName=== row.firstName)).length
     if (this.firstName !== row.firstName) {
       this.firstName = row.firstName
       return {
         rowspan: length,
         colspan: 1
       }
     } else {
       return {
         rowspan: 0,
         colspan: 0
       }
     }
   }

objectSpanMethod({ row, column, rowIndex, columnIndex }) {
      const length = this.list.filter(item => (item.firstName=== row.firstName)).length
      const firstName  = this.list[rowIndex - 1]?.firstName || '' 根据自己需要定义在方法内
      if (firstName !== row.firstName) {
       return {
         rowspan: length,
         colspan: 1
       }
     } else {
       return {
         rowspan: 0,
         colspan: 0
       }
     }
   }