JSFiddle - React, Tailwind, and code Playground
HTML
<select id="mySelect" class="a b c">
<option value="1">A</option>
<option value="2">B</option>
<option value="3">C</option>
</select>
JavaScript
$('#mySelect').change(function () {
var className = $( this ).attr( 'class' );
var exp = className.split(' ');
var newClass = $.map(exp, function (e,i) {
return '.' + e;
}).join( ' ' );
alert(newClass)
}).change();