JSFiddle - React, Tailwind, and code Playground
HTML
<select id="selectbox">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<input id="first-textbox" type="text" readonly>
<input id="second-textbox" type="text">
JavaScript
$('#selectbox').on('change', function() {
$("#first-textbox").val($(this).val());
$("#second-textbox").val($(this).val());
});