js 关于时间的代码块

function getDateStr(datestr){
    var year = datestr.slice(0, 4);
    var month = datestr.slice(4, 6);
    var day = datestr.slice(6, 8);
    return year + "-" + month + "-" + day;
}

function toDateStr(datestr, n){
    var year = datestr.slice(0, 4);
    var month = datestr.slice(5, 7);
    var int_day = parseInt(datestr.slice(8, 10), 10) + n;
    var day = int_day < 10 ? "0" + int_day : "" + int_day;
    return year + month + day;
}

function getTimeStr(datestr){
    var hh = datestr.slice(8, 10);
    var mm = datestr.slice(10, 12);
    var ss = datestr.slice(12, 14);
    return hh + ":" + mm;
}

function getDate(m, d){
    var date = new Date();
    if (m) {
        date = new Date(date.getFullYear(), date.getMonth() + m, date.getDate(), date.getHours(), date.getMinutes(), date.getSeconds());
    }
    if (d) {
        date = new Date(date.getFullYear(), date.getMonth(), date.getDate() + d, date.getHours(), date.getMinutes(), date.getSeconds());
        
    }
    var year = date.getFullYear();
    var month = date.getMonth() + 1;
    var day = date.getDate();
    var datestr = year + (month < 10 ? "0" + month : "" + month) + (day < 10 ? "0" + day : day)
    return datestr;
}

function getNowDateTime(){
    var date = new Date();
    var year = date.getFullYear();
    var month = date.getMonth() + 1;
    var day = date.getDate();
    var hh = date.getHours() < 10 ? "0" + date.getHours() : date.getHours() + "";
    var mm = date.getMinutes() < 10 ? "0" + date.getMinutes() : date.getMinutes() + "";
    //var ss=date.getSeconds()<10?"0"+date.getSeconds():date.getSeconds()+"";
    var datetimestr = year + (month < 10 ? "0" + month : "" + month) + (day < 10 ? "0" + day : day) + hh + mm;
    return datetimestr;
}