Untitled

<!DOCTYPE html>
 <html>
 <head>
 	<title>Register</title>
 </head>
 <body>
	 <form action="#" method="POST" id = "myform">
	 	<fieldset>
	 		<legend>Fill up the form</legend>
	 		<label>
	 			Full Name<input type = "text" name = "fullname" id="fullname">
	 		</label>
	 		<br><br>
	 		<label>
	 			Username:<input type = "text" name = "username" id="username">
	 		</label>
	 		<br><br>
	 		<label>
	 			Password:<input type = "password" name = "password" id="password">
	 		</label>
	 		<br><br>
	 		<label>
	 			Email:<input type = "email" name = "email" id = "email">
	 		</label>
	 		<br><br>
			<input type = "submit" value = "Submit">
	 	</fieldset>
	 </form>
	 <script>
	 	function formValidator(){
	 		var fullname = document.getElementById('fullname').value;
	 		var username = document.getElementById('username').value;
	 		var password = document.getElementById('password').value;
	 		var email = document.getElementById('email').value;

	 		if(fullname==""){
	 			alert("Name can't be empty.");
	 			return false;
	 		}
	 		var fullnameREGEX = /^[A-Z][a-z]+\s[A-Z][a-z]+$/;
	 		if(!fullnameREGEX.test(fullname)){
	 			alert("Enter a valid name.");
	 			return false;
	 		}
	 		if(username==""){
	 			alert("Username can't be empty.");
	 			return false;
	 		}
	 		var usernameREGEX = /^[a-z][a-z0-9]+$/;
	 		if(!usernameREGEX.test(username)){
	 			alert("Enter a valid user name");
	 			return false;
	 		}
	 		if(password==""){
	 			alert("Password can't be empty.");
	 			return false;
	 		}
	 		if(email==""){
	 			alert("Email can't be empty");
	 			return false;
	 		}
	 		var emailREGEX = /^[a-z][a-z0-9]+\@[a-z0-9]+.[a-z]{2,4}$/;
	 		if(!emailREGEX.test(email)){
	 			alert("Enter a valid email.");
	 		}
			return true;
	 	}
	 </script>
 </body>
 </html>