<script language="Javascript">
function download(filename, text) {
  var pom = document.createElement('a');
  pom.setAttribute('href', 'data:text/plain;charset=utf-8,' +

encodeURIComponent(text));
  pom.setAttribute('download', filename);

  pom.style.display = 'none';
  document.body.appendChild(pom);

  pom.click();

  document.body.removeChild(pom);
}
function addTextTXT()
{
    document.addtext.name.value = document.addtext.name.value + ".txt"
}
</script>




<form name="addtext" onsubmit="download(this['name'].value, this['text'].value)">

<textarea rows="10" cols="70" name="text" placeholder="Type your text here:"></textarea>
<br>
<input type="text" name="name" value="" placeholder="File Name">
<input type="submit" onclick="addTexttxt();" value="Save As TXT">

</form>