JSFiddle - React, Tailwind, and code Playground

HTML

<div class="form">
                                    <form  method="post" accept-charset="utf-8" class="form-horizontal" action="">
                                        <div class="form-group form-group">
                                            <label class="col-sm-4 control-label" for="username">Username:</label>
                                            <div class="col-sm-4">
                                                <input class="form-control" type="text" id="username" placeholder="john.doe" value="">
                                            </div>
                                            <div class="col-sm-4"></div>
                                        </div>
                                        <div class="form-group form-group">
                                            <label class="col-sm-4 control-label" for="password">Password:</label>
                                            <div class="col-sm-4">
                                                <input class="form-control" type="password" id="password" placeholder="Password" value = "">
                                                <div class="col-sm-4"></div>
                                            </div>
                                        </div>
                                        <div class="form-group form-group">
                                            <label class="col-sm-4 control-label" for="firstname">First Name:</label>
                                            <div class="col-sm-4">
                                                <input class="form-control" type="text" id="firstname" placeholder="John" value= "">
                                            </div>
                                            <div class="col-sm-4"></div>
                                        </div>
                                        <div class="form-group form-group">
                                            <label class="col-sm-4 control-label"...

JavaScript

$(document).ready(function() 
{
	$("#register").click(function() 
	{
		var username = $("#username").val();
		var password = $("#password").val();
		var firstname = $("#firstname").val();
		var secondname = $("#secondname").val();
		var email = $("#email").val();
		if (username == '' || password == '' || firstname == '' || secondname == '' || email == '') 
		{
			alert("Please fill all the fields!");
		} 
		else if ((password.length) < 8) 
		{
			alert("Password should have at least 8 characters in length!");
		}
		else 
		{
			$.post("register.php", {username1: username, password1: password, firstname1: firstname, secondname1: secondname, email1: email}, 
					function(data) 
					{
						if (data == 'You have successfully registered!') 
						{
							$("form-horizontal")[0].reset();
						}
						alert(data);
					});
		}
	});
});