Mastering JavaScript Promises

Callback-based promises versus Q-based promises

Say you have to interlink with callback-based instead of promise-based, what would be your options? The answer is Q provides Q.nfcall() and friends();, but most of the time, we have to rely on deferred:

var deferred = Q.defer();
FS.readFile("hoo.txt", "utf-8", function (error, text) {
    if (error) {
        deferred.reject(new Error(error));
    } else {
        deferred.resolve(text);
    }
});
return deferred.promise;

Normally, we can achieve it like this:

//normal way of handling rejected promises.
deferred.reject(new Error("Can't do it"));
//this is how we do it
var rejection = Q.fcall(function () {
    throw new Error("Can't do it");
});
deferred.resolve(rejection);

A few words on delay, timeout, and notify

There are situations ...