AJAX email form will not submit

I have a email signup form on my site that I recently added validation to.

Now the for will not send or provide an error message. When I check the inspector I see an error of "TypeError: null is not an object (evaluating 'document.getElementById(update[0]).innerHTML = update[1]')"

This is my contact.php file

 <?php
$to = "hello@interzonestudio.com";
$subject_prefix = ""; 

if(!isset($_GET['action']))

$subject = "Newsletter Sign Up"; //The senders subject
$message = trim($_GET['email']); //The senders subject
$email = trim($_GET['email']); //The senders email address

if (!filter_var($email, FILTER_VALIDATE_EMAIL) === false) {

mail($to,$subject,$message,"From: ".$email."");

echo 'contactarea|<div id="thanks">Thank you. We promise you won’t regret it.</div>';

else {
  echo("$email is not a valid email address");
}
?>

This is my form in HTML

<div id="contactarea">
<span style="font-family: 'Old Standard TT', serif;">Newsletter</span>
<form id="contactform" name="contactform" >
<input class ="email" type="text" name="email" id="inputbox" value="E-Mail"
onfocus="if(this.value==this.defaultValue)this.value='';" onblur="if(this.value=='')this.value=this.defaultValue;"/>
<input type="submit" value="Submit" name="send" onclick="sendemail(); return false; " class="signup" >
</form>
</div>

and this is my javascript

<script language="javascript">
function createRequestObject() {
    var ro;
    var browser = navigator.appName;
    if(browser == "Microsoft Internet Explorer"){
        ro = new ActiveXObject("Microsoft.XMLHTTP");
    }else{
        ro = new XMLHttpRequest();
    }
    return ro;
}
var http = createRequestObject();
function sendemail() {
var email = document.contactform.email.value;
document.contactform.send.disabled=true; 
http.open('get', 'contact.php?email='+email+'&action=send');
http.onreadystatechange = handleResponse;
http.send(null);

    setTimeout(function(){
        jQuery(document).find("#thanks").fadeOut();
    },3000);

}
function handleResponse() {
    if(http.readyState == 4){
        var response = http.responseText;
        var update = new Array();
        if(response.indexOf('|' != -1)) {
            update = response.split('|');
            document.getElementById(update[0]).innerHTML = update[1];
        }
    }
}
</script>

Any insight would be greatly appreciated.