JavaScript设置表单上传时文件个数的方法

<title>JavaScript设置表单上传时的文件个数</title><input type="button" name="button" value="添加附件" onclick="addInput()"><input type="button" name="button" value="删除附件" onclick="deleteInput()"><span id="upload"></span><script type="text/javascript"> var attachname = "attach"; var i=1;  function addInput(){  if(i>0){   var attach = attachname + i ;   if(createInput(attach))    i=i+1;  }  }   function deleteInput(){   if(i>1){   i=i-1;   if(!removeInput())    i=i+1;   }  }   function createInput(nm){   var aElement=document.createElement("input");   aElement.name=nm;  aElement.id=nm;  aElement.type="file";  aElement.size="50";  //aElement.value="thanks";   //aElement.onclick=Function("asdf()");    if(document.getElementById("upload").appendChild(aElement) == null)    return false;   return true;  }   function removeInput(nm){   var aElement = document.getElementById("upload");   if(aElement.removeChild(aElement.lastChild) == null)   return false;   return true;   } </script>