function init () {
    setLinkTargets();
    foobar();
}

function setLinkTargets () {
    if (!document.getElementsByTagName || !document.body) return false;

    var links = document.body.getElementsByTagName('a');

    for (var i = 0; i < links.length; i++) {
        var a = links[i];
        if(a.rel == 'extern') {
            a.target = '_blank';
        }
    }
}

function foobar () {
}

window.onload = init;