Set a specific date and year in a MS CRM date time field in the onchange event

function SetOneplusyearminus1date() {
    debugger;
    var start = Xrm.Page.getAttribute("msdyn_startdate").getValue();
    if (start != null) {
        var endDate = start.setDate(start.getDate() - 1); //To get the result date as -1 of original date
        var endYear = start.setYear(start.getFullYear() + 1);
        var ending = endYear + endDate;
        Xrm.Page.getAttribute("msdyn_enddate").setValue(ending);
    }
}