JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE HTML>
<html>
	<head>
	<title>BEAT | Login</title>
	<link rel="shortcut icon" href="images/favi.ico">
	</head>
	
	<body>
		<div id="login">
			<form>
				Name: <input type="text"></input>
				<br/>
				
				Age: <input type="text"></input>
				<br/>
				State: <select id="state">
						  <option value="Select">Select</option>
                          <option value="A">A</option>
						  <option value="B">B</option>
						  <option value="C">C</option>
						  <option value="D">D</option>
						</select>
						<br/>
				Region: <select id="region" >
							<option value="north">North</option>
							<option value="south">South</option>
						 </select>
			</form>
		</div>
	</body>
</html>

JavaScript

$('#region').css('display','none');
$('#state').on('change', function() {
    var state= $('#state').val();
    if(state=="A"||state=="B"){
        $('#region').css('display','block');
     }else{
         $('#region').css('display','none');
     }
});