话不多说,直接上代码

//拿到当前时间
function getLocalTime() {
    var now = new Date();
    var year= now.getFullYear();
    var month=now.getMonth()+1;
    var date=now.getDate();
    var hour=(now.getHours()<10)?("0"+now.getHours()):now.getHours();
    var minute=(now.getMinutes()<10)?("0"+now.getMinutes()):now.getMinutes();
    var second=(now.getSeconds()<10)?("0"+now.getSeconds()):now.getSeconds();
    return year+"/"+month+"/"+date +" "+hour+":"+minute+":"+second;
}
// 将时间转换成时间戳,ios的getTime方法对时间的格式有要求,下面做一下兼容
function getTime(time){
    var u = navigator.userAgent;
    var isAndroid = u.indexOf('Android') > -1 || u.indexOf('Adr') > -1;   //android终端
    var isiOS = !!u.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/); //ios终端
     if(isiOS){
        var t = new Date(time.replace(/-/g,'/')).getTime();
     }else{
        var t = new Date(time).getTime();
     }
     return t;     
   // var timeStr = null;
   // return timeStr = isiOS?new Date(time.replace(/-/g,'/')).getTime():new Date(time).getTime();
}
// 判断当前时间是否在规定起止时间内
function isDuringDate(){
    var cur = getLocalTime();
    var curDate = getTime(cur);
    var beginDate = getTime("2021/06/03 00:00:00");
    var endDate =  getTime("2025/06/20 23:59:59");
    if(curDate<beginDate){
        console.log("活动未开始")
    }else if(curDate>endDate){
        console.log("活动已结束")
    }
}