用js进行日期与天数的加减

//用js进行日期与天数的加减   function addDate(date, days) {     if (days == undefined || days == '') {         days = 1;     }     var d = new Date(date);     d.setDate(d.getDate() + days);     var m = d.getMonth() + 1;     return d.getFullYear() + '-' + m + '-' + d.getDate(); }