如何给一串数字用千分制表示？比如9999999999变成9，999，999，999

'99999999999'.replace(/\d{1,3}(?=(\d{3})+$)/g, '$&,')

有小数点的'99999999999.02'做千分之转换

'99999999999.02' 输出"99,999,999,999.02"
'99999999999.33333333' 输出"99,999,999,999.33,333,333"

方法一
'99999999999.33333333'.replace(/\d{1,3}(?=(\d{3})+(?:\.\d+)?$)/g, '$&,')
方法二
"123456789.12123".replace(/(?!^)(?=(\d{3})+(?:\.\d+)?$)/g, ',')

参考链接：

https://juejin.im/post/5d1702ed6fb9a07ef1619796?utm_source=wechat&from=groupmessage