获取当前月份的前一个月

getLastMonth(date) {
    var now = new Date(date)
    var year = now.getFullYear();
    var month = now.getMonth() + 1;
    var day = now.getDate();
    var nowMonthDay = new Date(year, month, 0).getDate(); // 当前月的总天数
    if (month - 1 <= 0) {
        day = day < 10 ? ('0' + day) : day
        return year - 1 + "-" + 12 + "-" + day 
    }; // 如果是1月，年数往前推一年
    var lastMonthDay = new Date(year, parseInt(month) - 1, 0).getDate();
    if (lastMonthDay >= day) {
        month = month -1;
        month = month < 10 ? ('0' + month) : month
        day = day < 10 ? ('0' + day) : day
        return year + "-" + month + "-" + day
    };
    if (day < nowMonthDay) {
        month = month -1;
        month = month < 10 ? ('0' + month) : month
        day = lastMonthDay - (nowMonthDay - day);
        day = day < 10 ? ('0' + day) : day
        return year + "-" + month + "-" + day
    }; // 1个月前所在月的总天数小于现在的天日期
    month = month -1;
    month = month < 10 ? ('0' + month) : month
    lastMonthDay = lastMonthDay < 10 ? ('0' + lastMonthDay) : lastMonthDay
    return year + "-" + month + "-" + lastMonthDay; // 当前天日期小于当前月总天数
},