window.onload = Loaded;

function Loaded() {
  SetNav();
}

function SetNav() {
  var slash = document.location.href.lastIndexOf('/') + 1;
  var page = document.location.href.substr(slash, document.location.href.lastIndexOf('.') - slash);
  if (page == '')
    page = 'index';
  ByID('nav-' + page).style.fontWeight = 'bold';
}

function ByID(id) {
  return (document.getElementById && document.getElementById(id)) ? document.getElementById(id) : false;
}