iview4.0 table合并项（指定x列+指定y行合并+可配置最后独立合计行）

修复了跨行数为1，导致首行显示异常的问题，代码链接已更新

不多bb，直接上图，上代码，上iview的代码实验田
功能：
1、可自定义配置跨行数
2、可指定从第x列开始合并
3、可配置尾行是否独立展示->做合计项


https://run.iviewui.com/qEntk4Ta

<template>
    <Table :columns="columns" :data="data" border :span-method="handleSpan"></Table>
  	跨行数(colCross)：<Input type="number" style="margin: 20px 0; width:80px" v-model="colCross"></Input>
  	从第 {{colStart}} 行开始(colStart)：<Input type="number" style="margin: 10px 0; width:80px" v-model="colStart"></Input>
		尾行是否独立展示(isSetTotalCol)：<Switch v-model="isSetTotalCol" />
</template>
<script>
    export default {
        data () {
            return {
              	isSetTotalCol: true,//是否设置最后一行为 合计项（独立展示）
                colCross: 3,//表示跨3行合并
                colStart: 1,//表示【跨行合并操作】从第一列开始
                columns: [
                    {
                        title: 'Date',
                        key: 'date'
                    },
                    {
                        title: 'Name',
                        key: 'name'
                    },
                    {
                        title: 'Age',
                        key: 'age'
                    },
                    {
                        title: 'Address',
                        key: 'address'
                    }
                ],
                data: [
                    {
                        name: 'John Brown',
                        age: 18,
                        address: 'New York No. 1 Lake Park',
                        date: '2016-10-01'
                    },
                    {
                        name: 'Jim Green',
                        age: 24,
                        address: 'London No. 1 Lake Park',
                        date: '2016-10-02'
                    },
                    {
                        name: 'Joe Black',
                        age: 30,
                        address: 'Sydney No. 1 Lake Park',
                        date: '2016-10-03'
                    },
                    {
                        name: 'Jon Snow',
                        age: 26,
                        address: 'Ottawa No. 2 Lake Park',
                        date: '2016-10-04'
                    },
                    {
                        name: 'John Brown',
                        age: 18,
                        address: 'New York No. 1 Lake Park',
                        date: '2016-10-05'
                    },
                    {
                        name: 'Jim Green',
                        age: 24,
                        address: 'London No. 1 Lake Park',
                        date: '2016-10-06'
                    },
                    {
                        name: 'Joe Black',
                        age: 30,
                        address: 'Sydney No. 1 Lake Park',
                        date: '2016-10-07'
                    },
                    {
                        name: '合计',
                        age: 26,
                        address: 'Ottawa No. 2 Lake Park',
                        date: '/'
                    },
                    {
                        name: '合计',
                        age: 26,
                        address: 'Ottawa No. 2 Lake Park',
                        date: '/'
                    },
                ]
            }
        },
      	computed: {
          	tabDataLen () {
              return this.data.length
            }
        },
        methods: {
            handleSpan ({ row, column, rowIndex, columnIndex }) {
                //将index从0开始变为从1开始,方便进行取余计算
              	return this.colCross!=1?this.handleSpanData(rowIndex+1, columnIndex+1): ''
            },
          	handleSpanData(rowIndex, columnIndex){
                if(this.isSetTotalCol){
                  //diff表示当前处理行与最后一行的差值
                  let diff = this.tabDataLen-rowIndex
                  if(!diff){
                    //diff=0 表示当前行为最后一行，需要阻止【跨行合并操作】、【删除操作】
                    return {rowspan: diff==0?1:0,colspan: diff==0?1:0};
                  }else if (rowIndex%this.colCross == 1 && columnIndex == this.colStart) {
                    //当前行数%跨行数 等于1的 时候：进行【跨行合并操作】
                    //同时不能让它跨行到最后一行
                    return {rowspan: diff<=(this.colCross-1)?diff:this.colCross,colspan: 1};
                  }else if (rowIndex%this.colCross != 1 && columnIndex == this.colStart) {
                    //当前行数%跨行数 不等于1的 时候：进行【删除操作】
                    //同时需要阻止【跨行合并操作】、【删除操作】
                    return {rowspan: diff==0?1:0,colspan: diff==0?1:0};
                  }
                } else {
                  if (rowIndex%this.colCross == 1 && columnIndex == this.colStart) {
                    //当前行数%跨行数 等于1的 时候：进行【跨行合并操作】
                    return {rowspan: this.colCross,colspan: 1};
                  }else if (rowIndex%this.colCross != 1 && columnIndex == this.colStart) {
                    //当前行数%跨行数 不等于1的 时候：进行【删除操作】
                    return {rowspan: 0,colspan:0};
                  }
                }
            }
        }
    }
</script>