html5 form validation example

<!DOCTYPE html>
<html lang="en-US">
<head>
<title>http://stackoverflow.com/questions/11381369/html5-required-and-jquery-submit</title>
<script type="text/javascript" src="http://code.jquery.com/jquery-latest.min.js"></script>
<script type="text/javascript">
<!--
    function validateForm(form) {
      if (form.username.value=='') {
        alert('Username missing');
        return false;
      }
      return true;
    }
//-->
</script>
</head>
<body>

<form action="index.php" name="loginform" method="post" onsubmit="if (!validateForm(this)) event.preventDefault();">
      <input name="username" placeholder="username" required="required" type="text" />
      <a href="" onclick="event.preventDefault(); $(document.forms.loginform).submit();">Login1</a>
      <a style="cursor:pointer;" onclick="$(document.forms.loginform).submit();">Login2</a>
      <input name="send" type="submit" value="Login3" />
      <input name="send" type="button" value="Login4" onclick="$(document.forms.loginform).submit();" />
</form>

</body>
</html>