PHP：
本周一

echo date('Y-m-d',(time()-((date('w')==0?7:date('w'))-1)*24*3600)); //w为星期几的数字形式,这里0为周日

本周日

echo date('Y-m-d',(time()+(7-(date('w')==0?7:date('w')))*24*3600)); //同样使用w,以现在与周日相关天数算

JS：
//本周周一

function showWeekFirstDay()     
{     
    var Nowdate=new Date();     
    var WeekFirstDay=new Date(Nowdate-(Nowdate.getDay()+6)*86400000);     
    M=Number(WeekFirstDay.getMonth())+1     
    return WeekFirstDay.getYear()+"-"+M+"-"+WeekFirstDay.getDate();     
}

本周最后天

//本周周天
function showWeekLastDay()     
{     
    var Nowdate=new Date();     
    var WeekFirstDay=new Date(Nowdate-(Nowdate.getDay()+6)*86400000);     
    var WeekLastDay=new Date((WeekFirstDay/1000+6*86400)*1000);     
    M=Number(WeekLastDay.getMonth())+1     
    return WeekLastDay.getYear()+"-"+M+"-"+WeekLastDay.getDate();     
}