function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      if (oldonload) {
        oldonload();
      };
      func();
    }
  }
}

function externalLinks() { 
	if (!document.getElementsByTagName) return; 
	var anchors = document.getElementsByTagName("a"); 
		for (var i=0; i<anchors.length; i++) { 
		  var anchor = anchors[i]; 
		  if (anchor.getAttribute("href") && 
		      anchor.getAttribute("rel") == "external") 
		    anchor.target = "_blank"; 
		} 
} 

addLoadEvent(externalLinks);