Erstatte value med Javascript i HTML formular

JScript kode 

 if(document.getElementById('Felt id').value == "Fornavn"){
   document.getElementById('Felt id').value = "";
 }

JScript kode 

 <!-- Begin MailChimp Signup Form -->
 <script type="text/javascript">
 // delete this script tag and use a "div.mce_inline_error{ XXX !important}" selector
 // or fill this in and it will be inlined when errors are generated
 var mc_custom_error_style = '';
 </script>
 <div id="mc_embed_signup">
 <form action="linktilmitid" method="post" id="mc-embedded-subscribe-form" name="mc-embedded-subscribe-form" class="validate" target="_blank">
 
 
 <div class="mc-field-group">
 <input type="text" value="Navn" onblur="if (this.value=='') this.value = 'Navn'" onfocus="if (this.value=='Navn') this.value = ''" name="FNAME" class="required" id="mce-FNAME">
 </div>
 
 <div class="mc-field-group">
 <input type="text" value="Email adresse" onblur="if (this.value=='') this.value = 'Email adresse'" onfocus="if (this.value=='Email adresse') this.value = ''" name="EMAIL" class="required email" id="mce-EMAIL">
 <div><input type="submit" value="" name="subscribe" id="mc-embedded-subscribe" class="btn"></div>
 </div>
         <div id="mce-responses">
             <div class="response" id="mce-error-response" style="display:none"></div>
             <div class="response" id="mce-success-response" style="display:none"></div>
         </div>
         
 </form>
 </div>
 <script type="text/javascript">
 var fnames = new Array();var ftypes = new Array();fnames[0]='EMAIL';ftypes[0]='email';fnames[1]='FNAME';ftypes[1]='text';
 try {
     var jqueryLoaded=jQuery;
     jqueryLoaded=true;
 } catch(err) {
     var jqueryLoaded=false;
 }
 var head= document.getElementsByTagName('head')[0];
 if (!jqueryLoaded) {
     var script = document.createElement('script');
     script.type = 'text/javascript';
     script.src = 'http://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js';
     head.appendChild(script);
     if (script.readyState && script.onload!==null){
         script.onreadystatechange= function () {
               if (this.readyState == 'complete') mce_preload_check();
         }    
     }
 }
 var script = document.createElement('script');
 script.type = 'text/javascript';
 script.src = 'http://downloads.mailchimp.com/js/jquery.form-n-validate.js';
 head.appendChild(script);
 var err_style = '';
 try{
     err_style = mc_custom_error_style;
 } catch(e){
     err_style = 'margin: 1em 0 0 0; padding: 1em 0.5em 0.5em 0.5em; background: ERROR_BGCOLOR none repeat scroll 0% 0%; font-weight: bold; float: left; z-index: 1; width: 80%; -moz-background-clip: -moz-initial; -moz-background-origin: -moz-initial; -moz-background-inline-policy: -moz-initial; color: ERROR_COLOR;';
 }
 var head= document.getElementsByTagName('head')[0];
 var style= document.createElement('style');
 style.type= 'text/css';
 if (style.styleSheet) {
   style.styleSheet.cssText = '.mce_inline_error {' + err_style + '}';
 } else {
   style.appendChild(document.createTextNode('.mce_inline_error {' + err_style + '}'));
 }
 head.appendChild(style);
 setTimeout('mce_preload_check();', 250);
 
 var mce_preload_checks = 0;
 function mce_preload_check(){
     if (mce_preload_checks>40) return;
     mce_preload_checks++;
     try {
         var jqueryLoaded=jQuery;
     } catch(err) {
         setTimeout('mce_preload_check();', 250);
         return;
     }
     try {
         var validatorLoaded=jQuery("#fake-form").validate({});
     } catch(err) {
         setTimeout('mce_preload_check();', 250);
         return;
     }
     mce_init_form();
 }
 function mce_init_form(){
     jQuery(document).ready( function($) {
       var options = { errorClass: 'mce_inline_error', errorElement: 'div', onkeyup: function(){}, onfocusout:function(){}, onblur:function(){}  };
       var mce_validator = $("#mc-embedded-subscribe-form").validate(options);
       $("#mc-embedded-subscribe-form").unbind('submit');//remove the validator so we can get into beforeSubmit on the ajaxform, which then calls the validator
       options = { url: 'linktilmitid', type: 'GET', dataType: 'json', contentType: "application/json; charset=utf-8",
                     beforeSubmit: function(){
                         $('#mce_tmp_error_msg').remove();
                         $('.datefield','#mc_embed_signup').each(
                             function(){
                                 var txt = 'filled';
                                 var fields = new Array();
                                 var i = 0;
                                 $(':text', this).each(
                                     function(){
                                         fields[i] = this;
                                         i++;
                                     });
                                 $(':hidden', this).each(
                                     function(){
                                         if ( fields[0].value=='MM' && fields[1].value=='DD' && fields[2].value=='YYYY' ){
                                             this.value = '';
                                         } else if ( fields[0].value=='' && fields[1].value=='' && fields[2].value=='' ){
                                             this.value = '';
                                         } else {
                                             this.value = fields[0].value+'/'+fields[1].value+'/'+fields[2].value;
                                         }
                                     });
                             });
                         return mce_validator.form();
                     }, 
                     success: mce_success_cb
                 };
       $('#mc-embedded-subscribe-form').ajaxForm(options);      
       
     });
 }
 function mce_success_cb(resp){
     $('#mce-success-response').hide();
     $('#mce-error-response').hide();
     if (resp.result=="success"){
         $('#mce-'+resp.result+'-response').show();
         $('#mce-'+resp.result+'-response').html(resp.msg);
         $('#mc-embedded-subscribe-form').each(function(){
             this.reset();
         });
     } else {
         var index = -1;
         var msg;
         try {
             var parts = resp.msg.split(' - ',2);
             if (parts[1]==undefined){
                 msg = resp.msg;
             } else {
                 i = parseInt(parts[0]);
                 if (i.toString() == parts[0]){
                     index = parts[0];
                     msg = parts[1];
                 } else {
                     index = -1;
                     msg = resp.msg;
                 }
             }
         } catch(e){
             index = -1;
             msg = resp.msg;
         }
         try{
             if (index== -1){
                 $('#mce-'+resp.result+'-response').show();
                 $('#mce-'+resp.result+'-response').html(msg);            
             } else {
                 err_id = 'mce_tmp_error_msg';
                 html = '<div id="'+err_id+'" style="'+err_style+'"> '+msg+'</div>';
                 
                 var input_id = '#mc_embed_signup';
                 var f = $(input_id);
                 if (ftypes[index]=='address'){
                     input_id = '#mce-'+fnames[index]+'-addr1';
                     f = $(input_id).parent().parent().get(0);
                 } else if (ftypes[index]=='date'){
                     input_id = '#mce-'+fnames[index]+'-month';
                     f = $(input_id).parent().parent().get(0);
                 } else {
                     input_id = '#mce-'+fnames[index];
                     f = $().parent(input_id).get(0);
                 }
                 if (f){
                     $(f).append(html);
                     $(input_id).focus();
                 } else {
                     $('#mce-'+resp.result+'-response').show();
                     $('#mce-'+resp.result+'-response').html(msg);
                 }
             }
         } catch(e){
             $('#mce-'+resp.result+'-response').show();
             $('#mce-'+resp.result+'-response').html(msg);
         }
     }
 }
 
 </script>
 <!--End mc_embed_signup-->

HTML kode 

 <head>
 <script type="text/javascript">
 function cl(f){
   var inps = f.getElementsByTagName('input');
   for(var index in inps){
     var inp = inps[index];
     if(inp.type == "text"){
       if(inp.defaultValue == inp.value){
         inp.value = "";
       }
     }
   }
   var inps = f.getElementsByTagName('textarea');
   for(var index in inps){
     var inp = inps[index];
     if(inp.defaultValue == inp.value){
       inp.value = "";
     }
   }
 }
 </script>
 </head>
 <body>
 <?php
 var_dump($_POST);
 ?>
 <form onsubmit="return cl(this);" method="post">
 <input name="t1" type="text" value="Test"/>
 <input name="t2" value="Test"/>
 <textarea name="a1">TT</textarea>
   <input type="submit" name="submit" value="submit"/>
 </form>
 </body>