1.转换为yyyy年MM月dd日

var str = "2021-09-13";
    var reg =/(\d{4})\-(\d{2})\-(\d{2})/;
    var date = str.replace(reg,"$1年$2月$3日");
    alert(date);

2.转换为yyyy/MM/dd/

var str = "2021-09-13";
    var reg =/(\d{4})\-(\d{2})\-(\d{2})/;
    var date = str.replace(reg,"$1/$2/$3");
    alert(date);

3.转换为yyyyMMdd

var str = "2021-09-13";
    var reg =/(\d{4})\-(\d{2})\-(\d{2})/;
    var date = str.replace(reg,"$1$2$3");
    alert(date);