Doing processing on a text file uploaded

I want to upload a text file on a webpage, read it, and then in javascript do some computation on the content of the file, e.g by calling a function called:

  do_calculation().

Here is the code I have so far. But it is not complete as I don't know how to read the content of the file from: function do_calculation().

html code:

  <tr>
  <td>Select a File to Load:</td>
  <td><input type="file" id="pubkey"></td>
  <output id="result" />
  <td><button onclick="loadFileAsText()">Load Selected File</button><td>
  </tr>

Javascript code:

 <script type="text/javascript">


function loadFileAsText(){
  var fileToLoad = document.getElementById("pubkey").files[0];

  var fileReader = new FileReader();
  fileReader.onload = function(fileLoadedEvent){
       var textFromFileLoaded = fileLoadedEvent.target.result;
      document.getElementById("result").value = textFromFileLoaded;
  };

   fileReader.readAsText(fileToLoad, "UTF-8");


  }

   function do_calculation(){

   }

   </script>

Moreover, I'd like to know how I can work on two uploaded files.