计算两个日期之间的天数

calculateData(beginTime,endTime){
//月份应该是0-11的
const newBeginTime=beginTime.slice(0,4)+'- 
'+beginTime.slice(4,6)+'-'+beginTime.slice(6,8);
const newEndTime=endTime.slice(0,4)+'-'+endTime.slice(4,6)+'-'+endTime.slice(6,8);
const countSecond=Date.parse(newEndTime)-Date.parse(newBeginTime);
const countDay=countSecond/(24*60*60*1000)
return countDay+1

}

1月1号到一月二号算两天

// 获取当前的8位字符串
    let myDate = new Date();
    let year=myDate.getFullYear(); 
    let month=myDate.getMonth()+1;
        month=month>9?month:('0'+month);
    let day=myDate.getDate();
        day=day>9?day:('0'+day)
    let nowday=year+month+day+'';

<script type="text/javascript">
// 获取当前时间戳(以s为单位)
var timestamp = Date.parse(new Date());
timestamp = timestamp / 1000;
//当前时间戳为：1403149534
console.log("当前时间戳为：" + timestamp);
 
// 获取某个时间格式的时间戳
var stringTime = "2014-07-10 10:21:12";
var timestamp2 = Date.parse(new Date(stringTime));
timestamp2 = timestamp2 / 1000;
//2014-07-10 10:21:12的时间戳为：1404958872 
console.log(stringTime + "的时间戳为：" + timestamp2);
 
// 将当前时间换成时间格式字符串
var timestamp3 = 1403058804;
var newDate = new Date();
newDate.setTime(timestamp3 * 1000);
// Wed Jun 18 2014 
console.log(newDate.toDateString());
// Wed, 18 Jun 2014 02:33:24 GMT 
console.log(newDate.toGMTString());
// 2014-06-18T02:33:24.000Z
console.log(newDate.toISOString());
// 2014-06-18T02:33:24.000Z 
console.log(newDate.toJSON());
// 2014年6月18日 
console.log(newDate.toLocaleDateString());
// 2014年6月18日 上午10:33:24 
console.log(newDate.toLocaleString());
// 上午10:33:24 
console.log(newDate.toLocaleTimeString());
// Wed Jun 18 2014 10:33:24 GMT+0800 (中国标准时间)
console.log(newDate.toString());
// 10:33:24 GMT+0800 (中国标准时间) 
console.log(newDate.toTimeString());
// Wed, 18 Jun 2014 02:33:24 GMT
console.log(newDate.toUTCString());
 
Date.prototype.format = function(format) {
    var date = {
       "M+": this.getMonth() + 1,
       "d+": this.getDate(),
       "h+": this.getHours(),
       "m+": this.getMinutes(),
       "s+": this.getSeconds(),
       "q+": Math.floor((this.getMonth() + 3) / 3),
       "S+": this.getMilliseconds()
    };
    if (/(y+)/i.test(format)) {
       format = format.replace(RegExp.$1, (this.getFullYear() + '').substr(4 - RegExp.$1.length));
    }
    for (var k in date) {
       if (new RegExp("(" + k + ")").test(format)) {
           format = format.replace(RegExp.$1, RegExp.$1.length == 1
              ? date[k] : ("00" + date[k]).substr(("" + date[k]).length));
       }
    }
    return format;
}
console.log(newDate.format('yyyy-MM-dd h:m:s'));
 
</script>