I'm trying to stop people from sending me blank emails through my contact us on my website. On my main website I have succeeded with the following javascript:

```
<script type="text/javascript">
function checkForm(f)
{
if (f.elements['cf_name'].value == "" && f.elements['cf_email'].value == "" &&          f.elements['cf_message'].value == "")
{
    alert("You have not filled in all of the required fields.");
    return false;
}
else
{
    f.submit();
    return false;
}
}
</script>

```

Although this works, when I implemented the same on my mobile website, people are still able to send blank emails.

The HTML code I used for the form check is:

```
<form action="contact.php" method="post" name="sform" onSubmit="return checkForm(this);">

```

So my question is how do i stop form submission if the fields are empty, on a mobile device (specifically iPhone)