javascript get form element

<script language="javascript">

function validate_form() {

var username = document.forms['register'].elements['user_username'].value;
var password = document.forms['register'].elements['user_pass'].value;
var name = document.forms['register'].elements['user_name'].value;
var email = document.forms['register'].elements['user_email'].value;
var phone = document.forms['register'].elements['user_phone'].value;

}
</script>

<form name="register" method="post" action="register.php">
<table>
<tr><td>Username</td><td>: <input type="text" name="user_username"></td></tr>
<tr><td>Password</td><td>: <input type="text" name="user_pass"></td></tr>
<tr><td>Name</td><td>: <input type="text" name="user_name"></td></tr>
<tr><td>Email Address</td><td>: <input type="text" name="user_email"></td></tr>
<tr><td>Phone number</td><td>: <input type="text" name="user_phone"></td></tr>
<tr><td colspan="2" align="center"><input type="Button" onClick = "validate_form()" value="Register"></td></tr>
</table>
</form>