<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script>
$(function () {
$('#MultiSelect').on('change', function (a, b, c) {
var options = a.target.selectedOptions;
var temp = [];
for (var i = 0; i < options.length; i++) {
var item = options[i];
var value = item.value;
var text = item.text;
temp.push(value);
}
var selectedValuesCSV = temp.join(',');
$('#listBoxValue').val(selectedValuesCSV)
});
});
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ListBox runat="server" ID="MultiSelect" AutoPostBack="false" SelectionMode="multiple" ></asp:ListBox>
</div>
<div>
<p>The Selected Value is:</p><asp:TextBox ID="listBoxValue" runat="server" ></asp:TextBox>
</div>
</form>
</body>
</html>