nodeify-function

Q helper for nodeifying a promise returning function.

This method is useful for creating dual promise/callback APIs, i.e. APIs that
return promises but also accept Node.js-style callbacks. Q provides a helper
for nodeifying promises:
promise.nodeify(callback).
This function is the inverse: rather than nodeifying the promise, we can simply
nodeify the function containing the promise. For example:

`` js
var createUser = function (userName, userData) {
return database.ensureUserNameNotTaken(userName)
.then(function () {
return database.saveUserData(userName, userData);
});
}

createUser('Bob', { age: 42 })
.then(function (result) {
// …
}, function (error) {
// …
});

// Without nodeifyFunction

var createUserNodeified = function (userName, userData, callback) {
createUser(userName, userData)
.nodeify(callback);
};

// With nodeifyFunction: a Q helper that abstracts the above into a
// higher-order function

var createUserNodeified = nodeifyFunction(createUser);

createUserNodified('Bob', { age: 42 }, function (error, result) {
// …
});
``