backend.js

    function addEvent(elem, event, fn) {
        if(!elem) { return false; }
        if (elem.addEventListener) {
            elem.addEventListener(event, fn, false);
        } else {
            elem.attachEvent("on" + event, function() {
                // set the this pointer same as addEventListener when fn is called
                return(fn.call(elem, window.event));
            });
        }
    }

/**
 * @author Juerg Rast
 */

/* Tooltipp Funktionen */
wmtt = null;
document.onmousemove = updateWMTT;
function updateWMTT(e) {
  if (wmtt != null) {
    x = (document.all) ? window.event.x + wmtt.offsetParent.scrollLeft : e.pageX;
    y = (document.all) ? window.event.y + wmtt.offsetParent.scrollTop  : e.pageY;
    wmtt.style.left = (x + 20) + "px";
    wmtt.style.top   = (y + 20) + "px";
  }
}

function showWMTT(id) {
  wmtt = document.getElementById(id);
  wmtt.style.display = "block"
}

function hideWMTT() {
  wmtt.style.display = "none";
}

/* Kategorieanzeige Funktionen */
function toggle_visibility(id) {
        /* Toggle plus/minus Image */
        var plus = new Image;
        plus.src = theme_url+"/images/plus_16.png";
        var minus = new Image;
        minus.src = theme_url+"/images/minus_16.png";

        var img_src = document.images['plus_minus_' + id].src;
    if (img_src == plus.src) {
        document.images['plus_minus_' + id].src = minus.src;
    }
    else {
        document.images['plus_minus_' + id].src = plus.src;
    }
        /* Toggle visibility of subcategorie */
    if (document.getElementById(id).style.display == "block") {
        document.getElementById(id).style.display = "none";
    }
    else {
        document.getElementById(id).style.display = "block";
    }
}