JSFiddle - React, Tailwind, and code Playground
HTML
<select id="slector">
<option value="">Please slect no</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<button id="submit">Submit</button>
JavaScript
$(document).ready(function(e) {
$(document).on('click','#submit',function(){
var a = $('#slector').val();
if (a=="")
alert('please select something');
else
alert('selected value:'+a);
});
});