How to extend q.promise in node.js? | وب سایت شخصی ناصر تراب زاده

I need to extent q.promise with my own functions, I tried:

defer = q.defer();
defer.promise.prototype.funcName = function () {
    // my function
}

witch returns following error:

TypeError: Cannot set property 'funcName' of undefined

How should I properly extend q.promise?