js日期处理

/**
 * 获取两个日期相差天数
 */
function getDays(time1, time2) {
    if(typeof time1 === 'string') {
        time1 = parse(time1);
    }
    if(typeof time2 === 'string') {
        time2 = parse(time2);
    }
    return parseInt(Math.abs(time1.getTime() - time2.getTime()) / (1000 * 60 * 60 * 24));
}
//将num左补0为len长度的字符串
function lpadNum(num, len) {
    var l = num.toString().length;
    while(l < len) {
        num = "0" + num;
        l++;
    }
    return num;
}
/**
 * 将字符串时间转换成 Date
 */
function parse(str) {
    // 这里需要将'-'替换成'/' 因为年-月-日 这种格式解析出来会有问题
    return new Date(str.replace(/-/g, "/"));
}
/**
 * 将Date解析成字符串
 */
function formatDateTime(time) {
    if(typeof time === 'string') {
        time = parse(time);
    }
    return yyyymmdd(time) + " " + hhmmss(time)
}

function yyyymmdd(time, joinStr = '-') {
    if(typeof time === 'string') {
        time = parse(time);
    }
    let year = time.getFullYear();
    let month = time.getMonth() + 1;
    let date = time.getDate();
    return year + joinStr + lpadNum(month,2) + joinStr + lpadNum(date,2);
}

function hhmmss(time) {
    if(typeof time === 'string') {
        time = parse(time);
    }
    let hours = time.getHours();
    let minutes = time.getMinutes();
    let seconds = time.getSeconds();
    return lpadNum(hours,2) + ":" + lpadNum(minutes,2) + ":" + lpadNum(seconds,2);
}

function hhmm(time) {
    if(typeof time === 'string') {
        time = parse(time);
    }
    let hours = time.getHours();
    let minutes = time.getMinutes();
    return lpadNum(hours,2) + ":" + lpadNum(minutes,2);
}

function showSimpleTime(time) {
    // 如果传的是字符串, 则需要将其解析成Date类型
    if(typeof time === 'string') {
        time = parse(time);
    }
    let nowDate = new Date();
    let fullYear = time.getFullYear();
    let month = time.getMonth() + 1;
    let date = time.getDate();
    let hours = time.getHours();
    let minutes = time.getMinutes();
    // 判断 当前时间的凌晨 与 传入时间的凌晨 相差多少天
    let dayCount = getDays(parse(yyyymmdd(time)), parse(yyyymmdd(nowDate)));
    // 同一天
    if(dayCount === 0) {
        return lpadNum(hours,2) + ":" + lpadNum(minutes, 2);
    }
    // 是否是昨天
    if (dayCount === 1) {
        return "昨天 " + lpadNum(hours,2) + ":" + lpadNum(minutes, 2);
    }
    // 是否是前天
    if (dayCount === 2) {
        return "前天 " + lpadNum(hours,2) + ":" + lpadNum(minutes, 2);
    }
    // 同一年
    if(fullYear === nowDate.getFullYear()) {
        return month + "/" + date + " " + lpadNum(hours,2) + ":" + lpadNum(minutes, 2);
    }
    return fullYear + "/" + month + "/" + date;
}