function externalLinks() {
  var anchors = getElementsByClassName("external");
  for (var i = 0; i < anchors.length; i++) {
    if (anchors[i].getAttribute("href")) anchors[i].target = "_blank";  // Target new window
  }
}

// Onload
if (window.addEventListener) {
  window.addEventListener('load', externalLinks, false);
}
else if (window.attachEvent) {
  window.attachEvent('onload', externalLinks);
}
else {
  window.onload = externalLinks;
}