window.onload = function () {
    setTooltip(document.getElementById('circle-blue'));
    setTooltip(document.getElementById('circle-purp'));
    setTooltip(document.getElementById('circle-orange'));
    setTooltip(document.getElementById('circle-lightorange'));
    setTooltip(document.getElementById('circle-grey'));
}
function setTooltip(elem) {
    if(elem){
        var title = getChildByName(elem, 'title');
        elem.onmouseover = function () {
            title.style.display = 'block';
        };
        elem.onmouseout = function () {
            title.style.display = 'none';
        };
    }
}

function getChildByName(elem, name) {
    var childs = elem.children;
    for(var i in childs){
        if(childs.item(i).getAttribute('name') == name){
            return childs.item(i);
        }
    }
}