Textarea auto-scroll to the bottom

Question

I have a textarea that I append data to with textarea.value += "more text\\n"; and I would like it to "stay" scrolled to the bottom, so it would always show the last line.

I have read that I should do:

var textarea = document.getElementById('textarea_id');
textarea.scrollTop = textarea.scrollHeight;

But I tried that ( http://jsfiddle.net/BenjiWiebe/mya0u1zo/ ) and I can't get it to work.

What am I doing wrong?

Answer 1

You need to set scrollTop each time you append text:

var textarea = document.getElementById('textarea_id');
setInterval(function(){
    textarea.value += Math.random()+'\n';
    textarea.scrollTop = textarea.scrollHeight;
}, 1000);

http://jsfiddle.net/mya0u1zo/2/

Answer 2

To answer the original question: since your string output ends with a newline, you should scroll before you output, not after (I keep my ids in an object called id):

function Output(Msg)
  {
  ...
  id.Log.scrollTop=id.Log.scrollHeight;
  SetValue('Log',out);
  }