获取某个日期的上一个月份

// 获取传入日期的上一个月时间（不传默认当前时间）
function getLastMonthDate(params) {
    var date = params ? new Date(params) : new Date()
    var daysInMonth = new Array([0], [31], [28], [31], [30], [31], [30], [31], [31], [30], [31], [30], [31])
    var strYear = date.getFullYear()
    var strDay = date.getDate()
    var strMonth = date.getMonth() + 1
    if (strYear % 4 == 0 && strYear % 100 != 0) {
        daysInMonth[2] = 29
    }
    if (strMonth - 1 == 0) {
        strYear -= 1
        strMonth = 12
    } else {
        strMonth -= 1
    }

    strDay = daysInMonth[strMonth] >= strDay ? strDay : daysInMonth[strMonth]

    if (strMonth < 10) {
        strMonth = '0' + strMonth
    }
    if (strDay < 10) {
        strDay = '0' + strDay
    }
    var datastr = strYear + '-' + strMonth + '-' + strDay
    return datastr
}