how to Add 1 year to startdate to get the end date in javascript

want a output like below

if Start Date is "01-03-2016" the End date should be "28-02-2017" if Start Date is "10-04-2016" the End date should be "09-04-2017"

I tried below code

if (dat <= 31 && dat >= 1 && month <= 12 && month >= 1) {

            var expiryDate = new Date(n1, month - 1, dat);

            expiryDate.setFullYear(expiryDate.getFullYear() + 1);
            var day = ('0' + expiryDate.getDate()).slice(-2);
            var month1 = ('0' + (expiryDate.getMonth() + 1)).slice(-2);
            var year = expiryDate.getFullYear();
            var month = getMonthName(month1);

            var wholeenddate = day + "-" + month + "-" + year;

but it's not produce desired output.Please Help to solve it.