背景：官方和网上的例子都很简单，实际项目开发中比较的一般都是对象数组，且属性值不一定全为数值，有可能为字符串,比如某个数据没有值，默认显示字符串："--"
需求：降序或者升序无数值的在最后面显示
开发步骤：
(1)HTML：<a-table @change='compare' :columns='columns'>
(2)methods:
compare(pagination, filters, sorter, { currentDataSource }) {
this.order = sorter.order
},
(3)data:
order:"",
columns :[
{
title: "序号",
dataIndex: "id",
key: "id",
},
{
title: "站点信息",
dataIndex: "station",
key: "station",
},
{
dataIndex: "",
slots: { title: "current_data_type_name" }, //标题，current_data_type_name为变量
scopedSlots: { customRender: "name" }, //用于每行数据显示
sorter: (a, b) => {
let an = isNaN(parseFloat(a[this.current_data_type])) ? (this.order === 'descend' ? -99999999: 9999999): a[this.current_data_type]
let bn = isNaN(parseFloat(b[this.current_data_type])) ? (this.order === 'descend' ? -99999999: 9999999): b[this.current_data_type]
return an - bn
},
},
];
//this.current_data_type标识对象的key