vue2 iview switch 使用render渲染，before-change阻断前传参数

由于iview switch组件的before-change不能直接传参数，所以通过一种变通的方法来传参，此方法对于开关前触发弹窗定制化提示非常有用

打印测试：

示例代码：

<template>
    <Table :columns="columns1" :data="data1"></Table>
</template>
<script>
    // 全局this
    var thatValue;
    export default {
        data () {
            return {
                switchOneInfo:{},
                columns1: [
                    {
                        title: 'Name',
                        key: 'name'
                    },
                    {
                        title: 'Age',
                        key: 'age'
                    },
                    {
                        title: 'Address',
                        key: 'address'
                    },
                    {
                      title: '开关',
                      key: 'is_show',
                      render:function(h,params){
                        return h('i-switch',{
                          props:{
                            value:params.row.is_show,
                            beforeChange:thatValue.handleBeforeChange // 阻断属性
                          },
                          on:{
                            "on-change":(value)=>{ // 状态更新
                              console.log('on-change:',value)
                            }
                          },
                          nativeOn:{
                            "mousedown":()=>{ // 监听组件原生事件mousedown,此事件在click之前触发
                              thatValue.switchOneInfo = {
                                name:params.row.name,
                                is_show:params.row.is_show
                              }
                            },
                          }
                        });
                      }
                    },
                ],
                data1: [
                    {
                        name: 'John Brown',
                        age: 18,
                        address: 'New York No. 1 Lake Park',
                        date: '2016-10-03',
                        is_show: false
                    },
                    {
                        name: 'Jim Green',
                        age: 24,
                        address: 'London No. 1 Lake Park',
                        date: '2016-10-01',
                        is_show: true
                    },
                    {
                        name: 'Joe Black',
                        age: 30,
                        address: 'Sydney No. 1 Lake Park',
                        date: '2016-10-02',
                        is_show: false
                    },
                    {
                        name: 'Jon Snow',
                        age: 26,
                        address: 'Ottawa No. 2 Lake Park',
                        date: '2016-10-04',
                        is_show: true
                    }
                ]
            }
        },
        created() {
          thatValue = this
        },
        methods:{
          handleBeforeChange () {
            console.log("handleBeforeChange:",this.switchOneInfo)
            return new Promise((resolve) => {
                this.$Modal.confirm({
                    title: '切换确认',
                    content: '您确认要切换开关状态吗？',
                    onOk: () => {
                        resolve();
                    }
                });
            });
          }
        }
    }
</script>