方法1

保留卡号的前4位和后4位，中间的都变成*号

> '6212268202014638888'.replace(/(?<=\d{4})\d+(?=\d{4})/," **** **** "); 
> //6212 **** **** 8888

方法2

> '6212268202014638888'.replace(/^(.{4})(?:\d+)(.{4})$/, "$1 **** **** $2"); 
> //6212 **** **** 8888