columns: {
  handler: function handler() {
    var colsWithId = this.makeColumnsId(this.columns);
    his.allColumns = (0, _util.getAllColumns)(colsWithId);
    this.cloneColumns = this.makeColumns(colsWithId);

    this.columnRows = this.makeColumnRows(false, colsWithId);
    this.leftFixedColumnRows = this.makeColumnRows('left', colsWithId);
    this.rightFixedColumnRows = this.makeColumnRows('right', colsWithId);
    this.rebuildData = this.makeDataWithSortAndFilter();
    this.handleResize();
    },
   deep: true
  },

columns: {
   handler: function handler() {
     //[Fix Bug]You may have an infinite update loop in watcher with expression "columns"
     var tempClonedColumns = (0, _assist.deepCopy)(this.columns);
     var colsWithId = this.makeColumnsId(tempClonedColumns);
     //[Fix Bug End]
     this.allColumns = (0, _util.getAllColumns)(colsWithId);
     this.cloneColumns = this.makeColumns(colsWithId);

     this.columnRows = this.makeColumnRows(false, colsWithId);
     this.leftFixedColumnRows = this.makeColumnRows('left', colsWithId);
     this.rightFixedColumnRows = this.makeColumnRows('right', colsWithId);
     this.rebuildData = this.makeDataWithSortAndFilter();
     this.handleResize();
     },
   deep: true
   },

<template>
 <div>
  单表头：
 <Table :columns="columns1" @on-row-click="onRowClick" :data="data1"></Table>
  多表头：
  <Table :columns="columns12" @on-row-click="onRowClick2" :data="data1" border height="500"></Table>
 </div>
</template>
<script>
 export default {
  data() {
   return {
    columns1: [
     {
      title: 'Name',
      key: 'name'
     },
     {
      title: 'Age',
      key: 'age'
     },
     {
      title: 'Address',
      key: 'address'
     }
    ],
    data1: [
     {
      name: 'John Brown',
      age: 18,
      address: 'New York No. 1 Lake Park',
      date: '2016-10-03'
     },
     {
      name: 'Jim Green',
      age: 24,
      address: 'London No. 1 Lake Park',
      date: '2016-10-01'
     },
     {
      name: 'Joe Black',
      age: 30,
      address: 'Sydney No. 1 Lake Park',
      date: '2016-10-02'
     },
     {
      name: 'Jon Snow',
      age: 26,
      address: 'Ottawa No. 2 Lake Park',
      date: '2016-10-04'
     }
    ],
    columns12: [{
     title: 'Name',
     align:'center',
     children: [{
      title: 'nickName',
      key: 'name',
     },
      {
       title: 'realName',
       key: 'name'
      }
     ]
    },
     {
      title: 'Age',
      key: 'age'
     },
     {
      title: 'Address',
      key: 'address'
     }
    ],
   }
  },
  methods: {
   onRowClick() {
    if('City'!==this.columns1[this.columns1.length-1].title) {
     this.columns1.splice(this.columns1.length, 0, {
      title: 'City',
      key: 'address'
     })
    }
   },
   onRowClick2() {
    if('City'!==this.columns12[this.columns12.length-1].title) {
     this.columns12.splice(this.columns12.length, 0, {
      title: 'City',
      key: 'address'
     })
    }
   }
  },
 }
</script>