How to create a proxy object for callback in Nodejs

Now I am profiling my nodejs app in order to find the duration of each method call and callbacks.

I already write some code to to proxy each method call like:

function addPerfProxyUnderPrototype(name, clazz) {
    var fn = clazz.prototype[name];
    clazz.prototype[name] = function () {
        // var newArgs = getProxyArgs(arguments);
        var s = new Date().getTime();
        // var result = fn.apply(this, newArgs);
        var result = fn.apply(this, arguments);
        var e = new Date().getTime();
        console.log('duration : ' + (e - s));
        return result;
    };
};

I can get duration of method calls by these code. As you may knew, in nodejs app, the arguments contains callback function. The nodejs app code like:

var clazz = function(){
}   
clazz.prototype.send = function(callback){
    // do somthing
    callback(err, data);
}

I want to create a proxy for the callback args to get duration.

function getProxyArgs(args) {
    var newArgs = [];
    for (var i = 0; i < args.length; i++) {
        var arg = args[i];
        if (typeof arg === 'function')) {
            newArgs.push(function () {
                var s = new Date().getTime();
                var result = arg.apply(undefined, arguments);
                var e = new Date().getTime();
                console.log('duration : ' + (e - s));
                return result;
            });
        } else {
            newArgs.push(arg);
        }
    }
    return newArgs;
};

Above code will lose 'this'. Any idea how to fix this?