SOURCE

function addDate(date, days) {
     if (days == undefined || days == '') {
         days = 1;
     }
     var date = new Date(date);
     date.setDate(date.getDate() + days);
     var month = date.getMonth() + 1; //月份从0开始所以需要+1
     var day = date.getDate();
     return date.getFullYear() + '-' + getFormatDate(month) + '-' + getFormatDate(day);
 }
 function getFormatDate(arg) {
	if (arg == undefined || arg == '') {
		return '';
	}

	var re = arg + '';
	if (re.length < 2) {
		re = '0' + re;
	}

	return re;
}
var edate = addDate('2021-08-22',30);
var sdate = addDate('2021-08-22',-30);

function getisrange(dt,s1,s2){
    //var dt = new Date(dt.replace(/\-/g, "\/"));
    //var s1 = new Date(s1.replace(/\-/g, "\/"));
    //var s2 = new Date(s2.replace(/\-/g, "\/"));
    if(dt >= s1 && dt <= s2){
        return true;
    }
    else{
        return false;
    }
}
console.log(edate.replace(/\-/g, "\/"));

console.log(sdate,edate);

console.log(getisrange('2021-09-21',sdate,edate));