Jak jsem ti psal, je to kosmetická úprava... hlavně mě tu nekamenujte, psal sem to narychlo tak tam třeba není kontrola existence apod.

<script language="JScript">

function WriteFile(filename,text)
{
   var fso, f, r
   var ForReading = 1, ForWriting = 2;
   fso = new ActiveXObject("Scripting.FileSystemObject")
   f = fso.OpenTextFile(filename, ForWriting, true)
   f.Write(text);
   f.Close();
}

function ReadFile(filename)
{
   var fso, f;
   var ForReading = 1, ForWriting = 2;
   fso = new ActiveXObject("Scripting.FileSystemObject");
   f = fso.OpenTextFile(filename, ForReading);
   return(f.ReadAll());
}

function read()
 {
   fi = document.getElementById("fle");

   el = document.getElementById("ta");
   el.innerText = ReadFile(fi.value);
 } 

function wrt()
 {
   fi = document.getElementById("fle");

   el = document.getElementById("ta");
   WriteFile(fi.value,el.innerText);
 } 

</script>

<input type="file" id="fle"><button onclick="read();">Načíst</button><br>
<textarea id="ta" style="width: 300px; height: 300px"></textarea><br>
<button onclick="wrt();">Uložit</button>