function get_addday(add, mode) {

    var sDate = '2020-03-10';

    var add = parseInt(add);

var yy = parseInt(sDate.substr(0, 4), 10);

var mm = parseInt(sDate.substr(5, 2), 10);

var dd = parseInt(sDate.substr(8, 2), 10);

if (mode == 'd') {

d = new Date(yy, mm - 1, dd + add);

}

    else if (mode == 'm') {

d = new Date(yy, mm - 1 + add, dd);

}

    else if (mode == 'y') {

d = new Date(yy + add, mm - 1, dd);

}

    d.setDate(d.getDate() - 1);

yy = d.getFullYear();

mm = d.getMonth() + 1; mm = (mm < 10) ? '0' + mm : mm;

dd = d.getDate(); dd = (dd < 10) ? '0' + dd : dd;

    var todate = yy+'-'+mm+'-'+dd;

    alert(todate);

}