var pages = ['/flash/flash1.html', '/flash/flash2.html', '/flash/flash3.html', '/flash/flash4.html' ];
var ifmPageID = 0;

function changeContent(ifmID) {
  var ifm = document.getElementById(ifmID);
  if(ifm) {
    ifmPageID++;
    if(ifmPageID > pages.length - 1) ifmPageID = 0;
    ifm.src = pages[ifmPageID];
  }
  return true;
}