i have added dynamically file upload control in javascript

<input type="file" name="file" id="File1" />
<input type="button" onclick="validatefile()">
</input>

function validatefile()
 {
   if( $('#File1').val() != ""){
       // file selected
      alert("file selected");

   }
   else{
       // no file selected
      alert("no file selected");
   }
}