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

    anchors[i].getAttribute("rel") == "external") {
        anchors[i].target = "_blank";
    }
}
}
window.onload = externalLinks;