สอบถามการแก้ปัญหา event onchange ของ Selec type เมื่อทำการ select แล้วค้าง

<script language="JavaScript">
	function resutName(CusID)
	{
		switch(CusID)
		{
			<?php
			$strSQL = "SELECT * FROM customer ORDER BY CustomerID ASC";
			$objQuery = mysqli_query($conn,$strSQL);
			while($objResult = mysqli_fetch_array($objQuery))
			{
			?>
				case "<?php echo $objResult["CustomerID"];?>":
				frmMain.txtName.value = "<?php echo $objResult["Email"];?>";
				break;
			<?php
			}
			?>
			default:
			 frmMain.txtName.value = "";
		}
	}
</script>

ส่วนที่ในทำการในเมนู select

<select name="txtUserIDno" OnChange="resutName(this.value);">
							<option value=""><-- Engineer inputs --></option>

<script src="vendor/jquery/jquery-3.2.1.min.js"></script>
<!--===============================================================================================-->
	<script src="vendor/animsition/js/animsition.min.js"></script>
<!--===============================================================================================-->
	<script src="vendor/bootstrap/js/popper.js"></script>
	<script src="vendor/bootstrap/js/bootstrap.min.js"></script>
<!--===============================================================================================-->
	<script src="vendor/select2/select2.min.js"></script>
	<script>
		$(".selection-2").select2({
			minimumResultsForSearch: 20,
			dropdownParent: $('#dropDownSelect1')
		});
	</script>