While I work on my new project, VirtualAssistant, I created simple code, which allows to add tooltip to any DOM element on page. Of course, I should pass as second argument some kind of callback, which draws tooltip baloon with text, because for now, it's simple 'title' HTML attribute added 'on the fly' :)

tooltip.js

var VAEngine = VAEngine || ( function() {
    function addTooltip(_element, _tooltipText) {
        var _elem = document.querySelector(_element);

        console.log("_elem: ", _elem);
        _elem.addEventListener('mouseover', function() {
            _elem.title = _tooltipText;
        });
    }

    return {
        addTooltip: addTooltip
    };
})();

// usage:
// VAEngine.addTooltip("#sample1", "This is sample tooltip number one");
// where:
// #sample1 - ID of DOM element
// secon argument - content of tooltip