Article: Activate TextBox if another option is selected in DropDownBox using JavaScript and jQuery
<html>
<head>
<script src="js/jquery-3.5.1.min.js"></script>
<script>
$(document).ready(function () {
$('#btn1').click(function () {
$('#Select1').append($("<option>" + $('#Txt1').val() + "</option>"));
return false;
});
});
</script>
</head>
<body>
<form id="form2">
<input type="txt1" id="text">
<select id="select1" name="select degree">
<option></option>
<option></option>
<option></option>
</select><br>
<br>
<input type="button" id="btn1" value="click">
</form>
</html>