gistfile1.txt

function probe(cb) {
    var wsCtor = window['MozWebSocket'] ? MozWebSocket : WebSocket;
    var socket = new wsCtor(uri, 'blah');
    socket.onopen = function () {
        // Send a probe
        socket.send(JSON.stringify({
            type: 'probe',
            data: {}
        }));
    };
    socket.onerror = function() {
       cb('Not supported');
    }
    socket.onmessage = function(e) {
        cb();
    }
    socket.onclose = function() {
        cb('Not supported');
    }
}