external_links.js

var links = document.getElementsByTagName("a");
var link_count = links.length;

var checkDomain = function(url) {
  if ( url.indexOf('//') === 0 ) { url = location.protocol + url; }
  return url.toLowerCase().replace(/([a-z])?:\/\//,'$1').split('/')[0];
};

var isExternal = function(url) {
  return ( ( url.indexOf(':') > -1 || url.indexOf('//') > -1 ) && checkDomain(location.href) !== checkDomain(url) );
};

for (var i = 0; i < link_count; i++) {
  if (isExternal(links[i].href)) {
    links[i].setAttribute('target', '_blank');
  }
}