function openTab(url) {
    var a = window.document.createElement("a");
    a.target = '_blank';
    a.href = url;

    var e = window.document.createEvent("MouseEvents");
    e.initMouseEvent("click", true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
    a.dispatchEvent(e);
};

openTab('http://www.google.com');