js把字符串(yyyymmdd)转换成日期格式（yyyy-mm-dd）

1、第一种写法：

var r="20112233".replace(/^(\d{4})(\d{2})(\d{2})$/, "$1-$2-$3")

2、第二种写法：　

var dateString = '19930701';
var pattern = /(\d{4})(\d{2})(\d{2})/;
var formatedDate = dateString.replace(pattern, '$1-$2-$3');