execute code on real time

Hi,
im making some sort of image gallery which displays only the image marked with an ID contained in a text file. I need that as soon as i update that text file with another ID, the image changes in real time to the new one. This is my code:

Code (text):

<script type=’text/javascript’>

      var primimg;

      function firstimage() {

        var xmlhttp;

        if (window.XMLHttpRequest)

        {

          xmlhttp=new XMLHttpRequest();

        }…

execute code on real time

See original post by supercain