js清空函数

<script type="text/javascript">
      
        //function for reset controls
        function ClearAllControls()
        {
            //set your validation controls prefix here.
            var validationControlsPrefix = "req";
            resetmsg(validationControlsPrefix);
              for (i=0; i<document.forms[0].length; i++)
              {
                    doc = document.forms[0].elements[i];
                    switch (doc.type)
                    {
                        case "text" :
                                doc.value = "";
                                break;
                          case "checkbox" :
                                doc.checked = false;
                                break;  
                          case "radio" :
                                doc.checked = false;
                                break;              
                          case "select-one" :
                                doc.options[doc.selectedIndex].selected = false;
                                doc.selectedIndex = 0;
                                break;                    
                          case "select-multiple" :
                                while (doc.selectedIndex != -1)
                                {
                                      indx = doc.selectedIndex;
                                      doc.options[indx].selected = false;
                                }
                                doc.selected = false;
                                break;
                         case "textarea":
                                doc.value = "";
                                break;
                          case "file" :
                              var browser=navigator.appName;
                             if(browser == 'Microsoft Internet Explorer')
                              {
                                 var fil = doc;
                                 //fil.select();
                                 n=fil.createTextRange();
                                 n.execCommand('delete');                         
                              }
                              else
                              {
                                 doc.value='';
                              }
                             break; 
                          default :
                                break;
                    }
              }
        }
      
        //function for reset validation controls
        function resetmsg(validationControlsPrefix)
        {
         
           var spans;
             var browser=navigator.appName;
             if(browser == 'Microsoft Internet Explorer')
              {
                spans = document.all.tags('span');
              }
              else
              {
                spans =  document.getElementsByTagName('span');
              }
            
            if (spans)
             {
                for (var i = 0; i < spans.length; i++)
                 {
                    var prefixLength = "" + validationControlsPrefix.length;
                    var currID = "" + spans[i].id
                    if ((currID != '') && (prefixLength != ''))
                       {
                          if (currID.substring(0,prefixLength) ==
     validationControlsPrefix)
                            {
                                spans[i].style.display = "none";
                             }
                       }
                 }
             }         
          
        }      
        </script>