1. yyyy年MM月dd 转 yyyy-MM-dd

substr() 方法提取字符串的一部分

substr(start, length) 方法从指定位置开始, 并返回指定长度的字符

substr() 方法不会更改原始字符串

function formatDate(dateString) {

        var year = " ", month = " ", day = " ";

        // 获取年月日在字符串中的索引

        const yearIndex = dateString.indexOf("年");

        const monthIndex = dateString.indexOf("月");

        const dayIndex = dateString.indexOf("日");

        // 根据索引位置截取数字部分

        year = dateString.substr(0, yearIndex);

        var monthString = dateString.substr(yearIndex + 1, monthIndex - yearIndex - 1);

        var dayString = dateString.substr(monthIndex + 1, dayIndex - monthIndex - 1);

        // 日期单位数需要补0

        month = monthString.length > 1 ? monthString : "0" + monthString;

        day = dayString.length > 1 ? dayString : "0" + dayString;

        return year + "-" + month + "-" + day;

}

var dateStr = "2023年4月13日";

formatDate(dateStr);        // 2023-04-13

2. yyyy-MM-dd 转 yyyy年MM月dd

var dateStr = "2023-04-13";

var reg = /(\d{4})\-(\d{2})\-(d{2})/;

var _date = str.replace(reg, "$1年$2月$3日");

alert(_date);

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