How to return a date period

function returnDatePeriod(returnParam) {

    var today = new Date();

    var returnPeriod = [];

    var startDate = "";

    var endDate = "";

    var d = new Date();

    var dd, mm, yy;

    var weekStartDay = 1;

    var weekEndDay = 0;

    switch (returnParam.toLowerCase()) {

        case "today":

            var mm = today.getMonth() + 1;

            var dd = today.getDate();

            startDate = today.getFullYear() + "-" + (mm < 10 ? "0" + mm : mm) + "-" + (dd < 10 ? "0" + dd : dd) + " 00:00:00";

            endDate = today.getFullYear() + "-" + (mm < 10 ? "0" + mm : mm) + "-" + (dd < 10 ? "0" + dd : dd) + " 23:59:59";

            break;

        case "thisweek":

            for (var i = 0; i < 7; i++) {

                d.setDate(today.getDate() - i);

                if (d.getDay() == weekStartDay) {

                    yy = d.getFullYear();

                    mm = d.getMonth() + 1;

                    dd = d.getDate();

                    i = 7;

                }

            }

            startDate = today.getFullYear() + "-" + (mm < 10 ? "0" + mm : mm) + "-" + (dd < 10 ? "0" + dd : dd) + " 00:00:00";

            for (var i = 0; i < 7; i++) {

                d.setDate(today.getDate() + i);

                if (d.getDay() == weekEndDay) {

                    yy = d.getFullYear();

                    mm = d.getMonth() + 1;

                    dd = d.getDate();

                    i = 7;

                }

            }

            endDate = today.getFullYear() + "-" + (mm < 10 ? "0" + mm : mm) + "-" + (dd < 10 ? "0" + dd : dd) + " 23:59:59";

            break;

        case "lastweek":

            for (var i = 0; i < 7; i++) {

                d.setDate(today.getDate() - i);

                if (d.getDay() == weekStartDay) {

                    d.setDate(d.getDate() - 7);

                    yy = d.getFullYear();

                    mm = d.getMonth() + 1;

                    dd = d.getDate();

                    i = 7;

                }

            }

            startDate = today.getFullYear() + "-" + (mm < 10 ? "0" + mm : mm) + "-" + (dd < 10 ? "0" + dd : dd) + " 00:00:00";

            for (var i = 0; i < 7; i++) {

                d.setDate(today.getDate() - i);

                if (d.getDay() == weekEndDay) {

                    yy = d.getFullYear();

                    mm = d.getMonth() + 1;

                    dd = d.getDate();

                    i = 7;

                }

            }

            endDate = yy + "-" + (mm < 10 ? "0" + mm : mm) + "-" + (dd < 10 ? "0" + dd : dd) + " 23:59:59";

            break;

    }

    returnPeriod.push({ start: startDate, end: endDate });

    return returnPeriod;

}