HTML + JS Meminimal karakter text pada html.

<!DOCTYPE html>
<html>
<head>
    <title></title>
    <script type="text/javascript">
        function validasi_input(form){
        var mincar = 5;
        if (form.username.value.length < mincar){
        alert("Panjang Username Minimal 5 Karater!");
        form.username.focus();
        return (false);
        }
       return (true);
        }
    </script>
</head>
<body>

<form method="post" action="aksi.php" onsubmit="return validasi_input(this)">
<p>Username: <input name="username" type="text"></p>
<p><input name="" type="submit" value="submit"></p>
</form>


</form>


</body>
</html>