Js获取系统当前时间展示

  setInterval(function () {
            var dateTime = new Date();
            var year = dateTime.getFullYear();
            var month = dateTime.getMonth() + 1;
            var ri = dateTime.getDate();
            var day;
            if (dateTime.getDay() == 6) {
                day = "六";
            }
            if (dateTime.getDay() == 1) {
                day = "一";
            }
            if (dateTime.getDay() == 2) {
                day = "二";
            }
            if (dateTime.getDay() == 3) {
                day = "三";
            }
            if (dateTime.getDay() == 4) {
                day = "四";
            }
            if (dateTime.getDay() == 5) {
                day = "五";
            }
            if (dateTime.getDay() == 0) {
                day = "日";
            }
            var hours = dateTime.getHours();
            if(hours< 10){
                hours = "0"+hours
            }
            var minutes = dateTime.getMinutes();
            if(minutes< 10){
                minutes = "0"+minutes
            }
            var seconds = dateTime.getSeconds();
            $(".time").html(year + "-" + month + "-" + ri + "&nbsp;&nbsp; " + hours + ":" + minutes + "&nbsp;&nbsp; 星期" + day);
        }, 1000)

function getDay(num, str) {
    var today = new Date();
    var nowTime = today.getTime();
    var ms = 24*3600*1000*num;
    today.setTime(parseInt(nowTime + ms));
    var oYear = today.getFullYear();
    var oMoth = (today.getMonth() + 1).toString();
    if (oMoth.length <= 1) oMoth = '0' + oMoth;
    var oDay = today.getDate().toString();
    if (oDay.length <= 1) oDay = '0' + oDay;
    return oYear + str + oMoth + str + oDay;
}
var yesterday = getDay(-1, '-');
var today = getDay(0, '-');
console.log(yesterday,today);