JavaScript 获取 YYYY-MM-DD 格式日期的上一月、下一月字符串_js获取上月格式

// 获取指定日期字符串上一月字符串：YYYY-MM-DD
function getPrevMonthFormatDate(formatDate) {
    if (formatDate.length != 10) {
        return null
    }
 
    let year = Number(formatDate.substr(0, 4));
    let month = Number(formatDate.substr(5, 2));
    let day = Number(formatDate.substr(8, 2));
 
    if (month == 1)
    {
        year = year - 1; 
        month = 12;
    }
    else
    {
        month = month - 1;
    }
 
    return formatInteger(year, 4) + '-' + formatInteger(month, 2) + '-' + formatInteger(day, 2);
}
 
// 获取指定日期字符串下一月字符串：YYYY-MM-DD
function getNextMonthFormatDate(formatDate) {
    if (formatDate.length != 10) {
        return null
    }
 
    let year = Number(formatDate.substr(0, 4));
    let month = Number(formatDate.substr(5, 2));
    let day = Number(formatDate.substr(8, 2));
 
    if (month == 12)
    {
        year = year + 1; 
        month = 1;
    }
    else
    {
        month = month + 1;
    }
 
    return formatInteger(year, 4) + '-' + formatInteger(month, 2) + '-' + formatInteger(day, 2);
}

其中 formatInteger 见 JavaScript 使用指定字符格式化整数_hzgisme的博客-CSDN博客