5-3 分组

<script>
    var  reg = /(\d{4})-(\d{2})-(\d{2})$/
    var str = '2021-06-06'
    //字符串替换 $1-$3  $1 为第一组
    var str = '12333456567'
    var newstr = str.replace(/(\d{3})(\d{4})(\d{4})/,"$1****$3")
    console.log(newstr)
</script>