JavaScript: Form Validation

[The Hobo]

What's wrong with this code?:

<script>
    function check(f) {
        if (f.title.value == "") {
            alert("You must have a subject.");
        } elseif (f.body.value == "") {
            alert("You must have a body in your post.");
        } elseif (f.body.value.length > 10000) {
            alert("Your message is too long. The max is 10000 characters.");
        } else {
             document.f.submit();
        }
    }
</script>
<form action="post.php" method="post">
...
<input type="button" value=" Submit " onClick="check(forms(0))">

It's just supposed to validate the form and make sure all the fields are filled.