$('#deptInput').on('input', function() {
$('#deptList').val(this.value).prop("selected", true);
});
$('#deptInput').on("blur", function() {
if($('#deptList').val()==null){
$('#deptInput').val("");
}
});
<input type="hidden" name="deptCode">
<select class="add_select" id="deptList" style="display: none;">
<c:forEach var="result" items="${deptCodeList}">
<option value="${result.detailCodeNm}" value2="${result.detailCode}">${result.detailCodeNm}</option>
</c:forEach>
</select>
<input type="text" list="list" id="deptInput" placeholder="Enter Search">
<datalist id ="list">
<c:forEach var="result" items="${deptCodeList}">
<option value="${result.detailCodeNm}"></option>
</c:forEach>
</datalist>
셀렉트박스를 숨겨놓고 datalist의 값과 select의 value를 비교해서 hidden input에 value2를 먹이는 내용
하다가 안쓸거같아서 적어는놓음