Mine

Silverlight.isInstalled = function(d) {
    var c = false,
    a = null;
    try {
        var b = null;
        if (Silverlight.ua.Browser == "MSIE") b = new ActiveXObject("AgControl.AgControl");
        else if (navigator.plugins["Silverlight Plug-In"]) {
            a = document.createElement("div");
            document.body.appendChild(a);
            if (Silverlight.ua.Browser == "Safari") a.innerHTML = '<embed type="application/x-silverlight" />';
            else a.innerHTML = '<object type="application/x-silverlight"  data="data:," />';
            b = a.childNodes[0]
        }
        document.body.innerHTML;
        if (b.IsVersionSupported(d)) c = true;
        b = null;
        Silverlight.available = true
    } catch(e) {
        c = false
    }
    if (a) document.body.removeChild(a);
    return c
};