Javascript Prepopulate text field

<style type="text/css">
<!--
.style1 {font-family: Tahoma, Arial}
.style2 {font-size: x-small}
.style3 {font-family: Tahoma, Arial; font-size: x-small; }
.style4 {color: #FF0000}
-->
</style>
<script type="text/javascript">
//no need of the following and hence removing it.
//var pagename; 
//pagename = document.location.href.substring(document.location.href.lastIndexOf('/'));
//document.frmSS5.CustomFields[12].value = pagename;
</script>
<!--
Do not modify the NAME value of any of the INPUT fields
the FORM action, or any of the hidden fields (eg. input type=hidden).
These are all required for this form to function correctly.
-->
<style>
 
        .myForm td, input, select, textarea, checkbox  {
                font-family: tahoma;
                font-size: 12px;
        }
 
        .required {
                color: red;
        }
 
</style>
<script type="text/javascript">
 
//document.write(document.URL);
</script>
<form action="http://constantcontact.seoconsultinguk.com/form.php?form=5" method="post" name="frmSS5" id="frmSS5" onSubmit="return CheckForm5(this);">
        <table border="0" cellpadding="2" class="myForm">
                <tr>
        <td><span class="required">*</span> 
Name:</td>
        <td><input type="text" name="CustomFields[11]" id="CustomFields_11_5" value=""></td>
    <td><span class="required">*</span> 
Your email:</td>
    <td><input type="text" name="email" value=""></td>
    <td><span class="required">*</span> 
Security code:</td>
    <td><script>
                                var SIDString = '';
 
                                function getRandomLetter() {
                                        return String.fromCharCode(getRandom(65, 90));
                                }
 
                                function getRandom(lowerBound, upperBound) {
                                        return Math.floor((upperBound - lowerBound + 1) * Math.random() + lowerBound);
                                }
 
                                function SetSID()
                                {
                                        if (SIDString.length > 0)
                                        {
                                                return SIDString;
                                        }
 
                                        sidc = 0;
 
                                        while (sidc < 32)
                                        {
                                                SIDString = SIDString + getRandomLetter();
                                                sidc++;
                                        }
                                        return SIDString;
                                }
                        </script>
        <script>
                                        var url = "http://constantcontact.seoconsultinguk.com/admin/resources/form_designs/captcha/index.php?c=" + getRandom(1,1000)+ "&ss=" + SetSID();
                                                document.write("<img src='" + url + "' alt='img'/>");
                                        </script>
        <br/>
        <input type="text" name="captcha" value=""></td>
    </tr><tr>
<!--removed the 'value' attribute-->
        <td><input name="CustomFields[12]" type="hidden" id="CustomFields_12_5" ></td>
        <td> </td>
    <td> </td>
    <td> </td>
    <td> </td>
    <td><input type="submit" value="Subscribe"></td>
    </tr><input type="hidden" name="format" value="h">
        </table>
</form>
 
<script language="javascript">
//added by me
document.getElementById("CustomFields_12_5").value = document.location.href.substring(document.location.href.lastIndexOf('/'));
 
                        function CheckMultiple5(frm, name) {
                                for (var i=0; i < frm.length; i++)
                                {
                                        fldObj = frm.elements[i];
                                        fldId = fldObj.id;
                                        if (fldId) {
                                                var fieldnamecheck=fldObj.id.indexOf(name);
                                                if (fieldnamecheck != -1) {
                                                        if (fldObj.checked) {
                                                                return true;
                                                        }
                                                }
                                        }
                                }
                                return false;
                        }
                function CheckForm5(f) {
                        if (f.email.value == "") {
                                alert("Please enter your email address.");
                                f.email.focus();
                                return false;
                        }
                
                                if (f.captcha.value == "") {
                                        alert("Please enter the security code shown");
                                        f.captcha.focus();
                                        return false;
                                }
                        
                        var fname = "CustomFields_11_5";
                        var fld = document.getElementById(fname);
                        if (fld.value == "") {
                                alert("Please enter a value for field Name");
                                fld.focus();
                                return false;
                        }
                
                                return true;
                        };
                
</script>

                                              

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