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Nodejs Promise for custom api

I am new to nodejs and using promise and actually this is my first real app with nodejs.
So i have been reading all day and i am a bit confused.
So this is my module :
function User() {
var self = this;
self.users = {};
self.start = function (user, botId) {
return new Promise(function () {
return get(user).then(function (data) {
debug(data);
if (data.botId.indexOf(botId) === false) {
return Repo.UserBotModel.addUser(user.id, botId).then(function () {
data.botId.push(botId);
return data;
});
} else
return data;
});
});
};
self.getDisplayName = function (user) {
if (user.real_name)
return user.real_name;
if (user.last_name)
return user.firstname + ' ' + user.last_name;
return user.first_name;
};
/**
* check if user exist in our database/memory cache and return it,
* otherwise insert in the database and cache it in memory and the return it
* #param user
*/
function get(user) {
return new Promise(function () {
//check if user is loaded in our memory cache
if (self.users.hasOwnProperty(user.id))
return self.users[user.id];
else {
//get from database if exist
return Repo.UserModel.get(user.id).then(function (rows) {
if (rows && rows.length) {
//user exist cache it and resolve
var data = rows[0];
if (data.botId && data.botId.length)
data.botId = data.botId.split(',');
else
data.botId = [];
self.users[user.id] = data;
//------------------------------ code execution reaches here
return data;
}
else {
//user dose not exist lets insert it
return Repo.UserModel.insert(user).then(function (result) {
return get(user);
});
}
});
}
});
}
}
I call the start method witch calls the private get method the call reaches return data;(marked with comment) but then function dose not gets executed in the start method ???
So what am i doing wrong?
UPDATE : Sorry I forgot to mention that I am using bluebird and not the native promise if that makes a difference?

You cannot return from the Promise constructor - you have to call resolve (expected to happen asynchronously). You're not supposed to use the Promise constructor at all here. You can just omit it, and it should work.

The methods from your Repo.UserModel already return promises, so you do not have to create new ones using new Promise.
You can read the values inside those promises using then.
then also provides a way to transform promises. If you return a value in a function passed to then, then will return a new promise that wraps the value you returned. If this value is a promise, it will be awaited.
To convert a value to a promise, you can use Promise.resolve.
Knowing that, you can simplify get like so:
function get(user) {
if (...) {
return Promise.resolve(...)
} else {
return Repo.UserModel.get(...).then(function(rows) {
...
return ...
})
}
}
This version of getwill always return a promise that you can use like so:
get(...).then(function(resultOfGet) {
// process resultOfGet
})

Node return BluebirdJS Promise

I have a small problem, this script works perfectly, with one problem, the "runTenant" method is not returning a promise (that needs resolving from "all()".
This code:
Promise.resolve(runTenant(latest)).then(function() {
end();
});
Calls this code:
function runTenant(cb) {
return new Promise(function() {
//global var
if (!Tenant) {
loadCoreModels();
Tenant = bookshelf.core.bs.model('Tenant');
}
new Tenant().fetchAll()
.then(function(tenants) {
if (tenants.models.length == 0) {
return;
} else {
async.eachSeries(tenants.models, function(tenant, next) {
var account = tenant.attributes;
Promise.resolve(db_tenant.config(account)).then(function(knex_tenant_config) {
if (knex_tenant_config) {
db_tenant.invalidateRequireCacheForFile('knex');
var knex_tenant = require('knex')(knex_tenant_config);
var knex_pending = cb(knex_tenant);
Promise.resolve(knex_pending).then(function() {
next(null, null);
});
} else {
next(null, null);
}
});
});
};
});
});
}
The code from runTenant is working correctly however it stalls and does not proceed to "end()" because the promise from "runTenant(latest)" isn't being resolved.
As if it weren't apparent, I am horrible at promises. Still working on getting my head around them.
Many thanks for any help/direction!

You should not use the Promise constructor at all here (and basically, not anywhere else either), even if you made it work it would be an antipattern. You've never resolved that promise - notice that the resolve argument to the Promise constructor callback is a very different function than Promise.resolve.
And you should not use the async library if you have a powerful promise library like Bluebird at hand.
As if it weren't apparent, I am horrible at promises.
Maybe you'll want to have a look at my rules of thumb for writing promise functions.
Here's what your function should look like:
function runTenant(cb) {
//global var
if (!Tenant) {
loadCoreModels();
Tenant = bookshelf.core.bs.model('Tenant');
}
return new Tenant().fetchAll().then(function(tenants) {
// if (tenants.models.length == 0) {
// return;
// } else
// In case there are no models, the loop iterates zero times, which makes no difference
return Promise.each(tenants.models, function(tenant) {
var account = tenant.attributes;
return db_tenant.config(account).then(function(knex_tenant_config) {
if (knex_tenant_config) {
db_tenant.invalidateRequireCacheForFile('knex');
var knex_tenant = require('knex')(knex_tenant_config);
return cb(knex_tenant); // can return a promise
}
});
});
});
}

Your promise in runTenant function is never resolved. You must call resolve or reject function to resolve promise:
function runTenant() {
return new Promise(function(resolve, reject) {
// somewhere in your code
if (err) {
reject(err);
} else {
resolve();
}
});
});
And you shouldn't pass cb in runTenant function, use promises chain:
runTenant()
.then(latest)
.then(end)
.catch(function(err) {
console.log(err);
});

You need to return all the nested promises. I can't run this code, so this isn't a drop it fix. But hopefully, it helps you understand what is missing.
function runTenant(cb) {
//global var
if (!Tenant) {
loadCoreModels();
Tenant = bookshelf.core.bs.model('Tenant');
}
return new Tenant().fetchAll() //added return
.then(function (tenants) {
if (tenants.models.length == 0) {
return;
} else {
var promises = []; //got to collect the promises
tenants.models.each(function (tenant, next) {
var account = tenant.attributes;
var promise = Promise.resolve(db_tenant.config(account)).then(function (knex_tenant_config) {
if (knex_tenant_config) {
db_tenant.invalidateRequireCacheForFile('knex');
var knex_tenant = require('knex')(knex_tenant_config);
var knex_pending = cb(knex_tenant);
return knex_pending; //return value that you want the whole chain to resolve to
}
});
promises.push(promise); //add promise to collection
});
return Promise.all(promises); //make promise from all promises
}
});
}

How to dispose resources in rejected promises with bluebird?

How can I dispose the serial when the promise is rejected?
The dispose function prints error for rejected promises.
Unhandled rejection TypeError: Cannot call method 'isOpen' of
undefined
var pingPort = function(port){
return new promise(function(resolve, reject){
var serial = new com.SerialPort(port.comName, {
baudrate: 19200,
parser: com.parsers.readline(lineEnd)
}, false);
serial.on("data", function(data){
if (data === responseUuid){
resolve(serial);
}
});
serial.open(function(err){
if (err){
//reject(serial)
}
else{
serial.write(pingUuid + lineEnd);
}
});
});
};
var dispose = function(port){
console.log(port.isOpen());
};
var findPort = function(){
com.listAsync().map(function(port){
return pingPort(port).timeout(100).catch(promise.TimeoutError, function(err) {
console.log("Ping timout: " + port.comName);
dispose(port);
}).catch(function(err){
console.log("Ping error: " + port.comName);
dispose(port);
});
}).each(dispose);
}();

This question almost answers itself, in that "promise" and "dispose" together beg you to consider the Promise Disposer Pattern, which is actually nothing more than judicious use of .then() or .finally() with a callback that disposes/closes something that was created/opened earlier.
With that pattern in mind, you will find it simpler to orchestrate disposal in pingPort() rather than findPort().
Assuming the code in the question to be broadly correct, you can chain finally() as follows :
var pingPort = function(port) {
var serial; // outer var, necessary to make `serial` available to .finally().
return new promise(function(resolve, reject) {
serial = new com.SerialPort(port.comName, {
baudrate: 19200,
parser: com.parsers.readline(lineEnd)
}, false);
serial.on('data', function(data) {
if(data === responseUuid) {
resolve(serial); //or resolve(port);
}
});
serial.open(function(err) {
if(err) {
reject('failed to open');
} else {
serial.write(pingUuid + lineEnd);
}
});
})
.finally(function() { // <<<<<<<<<<<
serial.close(); // "dispose".
});
};
Unlike .then, .finally's handler doesn't modify the value/reason, so can be placed in mid-chain without the need to worry about returning a value or rethrowing an error. This point is rather poorly made in the Bluebird documentation.
With disposal in pingPort(), findPort() will simplify as follows :
var findPort = function(){
com.listAsync().map(function(port) {
return pingPort(port).timeout(100)
.catch(promise.TimeoutError, function(err) {
console.log("Ping timout: " + port.comName);
})
.catch(function(err){
console.log("Ping error: " + port.comName);
});
});
}();
Going further, you may want to do more with the array of promises returned by .map(), but that's another issue.

Adding ajax in array for jQuery promise results in unexpected behaviour

I have an each statement which make separate AJAX requests and adds them to an array like:
var promises = [];
$items.each(function(k, v) {
promises.push(
$.ajax({
url: ...,
....
})
);
});
$.when.apply($, promises).done(function() { ... });
It seems that, I don't know the reason, for the first time when loading the page, or when it is deployed (I use ASP.NET MVC), the ajax is already executed for the first item when it reaches this breakpoint:
promises.push($.ajax ...
If I refresh the page, then everything works fine, and $.when correctly executes the ajax requests. However, if I deploy application, then the problem persists.
Why, for the first time, is the ajax request already called (not in $,.when)? Where is my mistake? I have no errors in JavaScript.

If the code isn't any more complex than the example, you can do something like this
var get_promises = function() {
var promises = [];
return function () {
if (promises.length === 0) {
$items.each(function(k, v) {
promises.push(
$.ajax({
url: ...,
....
})
);
});
}
return promises;
}
}());
$.when.apply($, get_promises()).done(function() { ... });
I can't believe I suggested the following!! But I'm going to own it :D
One way to do what you want is with so called "lazy" promises
a Promise/A+ polyfill - for Internet Explorer mainly (up to and including 11 - Edge, or whatever it's called in Windows 10, has native Promise)
<script src="https://www.promisejs.org/polyfills/promise-6.1.0.js"></script>
A lazy promise implementation, based on - https://github.com/then/lazy-promise - but modified to work with browser native promises - note, only tested in firefox, YMMV
var inherits = (function() {
if (typeof Object.create === 'function') {
return function inherits(ctor, superCtor) {
ctor.super_ = superCtor
ctor.prototype = Object.create(superCtor.prototype, {
constructor: {
value: ctor,
enumerable: false,
writable: true,
configurable: true
}
});
};
} else {
return function inherits(ctor, superCtor) {
ctor.super_ = superCtor;
var TempCtor = function () {};
TempCtor.prototype = superCtor.prototype;
ctor.prototype = new TempCtor();
ctor.prototype.constructor = ctor;
};
}
}());
inherits(LazyPromise, Promise);
function LazyPromise(fn) {
var promise;
if (!(this instanceof LazyPromise)) {
return new LazyPromise(fn);
}
if (typeof fn != 'function') {
throw new TypeError('fn is not a function');
}
this.then = function(onResolved, onRejected) {
return (promise = promise || new Promise(function(resolve, reject) {
setTimeout(function() {
try { fn(resolve, reject) }
catch (e) { reject(e) }
}, 0);
})).then(onResolved, onRejected);
};
}
Now to changes in your code - very minimal
var promises = [];
$items.each(function(k, v) {
promises.push(
new LazyPromise(function(resolve, reject) { // wrap the (broken) jQuery "promise" in a Lazy Promise
$.ajax({
url: ...,
....
})
.then(resolve, reject); // I assume $.ajax is "thenable", so resolve the wrapping Lazy promise;
}) // end of Lazy Promise wrapper
);
});
$.when.apply($, promises).done(function() { ... });
This is probably overkill, but it should do exactly what you requested in your question

Bluebird Promising the result of a heavy function

I've been using Bluebird a lot recently on a HAPI API development. I've just run into my first real problem, that perhaps my understanding or naivety has me stumped.
The following code is an example of what I am facing:-
var Promise = require('bluebird'),
stuff = require('../stuff');
module.exports = {
getSomething: function(request, reply) {
var p = Promise.resolve();
p = p.then(function() {
return db.find() //etc. etc.
});
p = p.then(function(resultFromPromise) {
//problems begin here
var data = stuff.doSomeReallyLongAndBoringFunction(resultFromPromise);
return data;
});
p.then(function(data) {
//no data here.
});
};
};
I've commented where the problems usually begin. the stuff.doSomeReallyLongAndBoringFunction() returns an object (using more promises concidently) and it's this object I want to access, but //no data here always fires before data returns. stuff.doSomeReallyLongAndBoringFunction() continues to run regardless and completes successfully, but after the code goes async, I don't know how to promise that function's return value back.
Can anyone offer any guidance? Please accept my apologies for any naivety in the question!
Help as always, is appreciated
NB just for clarity, stuff.doSomeReallyLongAndBoringFunction() does not return a Promise itself. Although, I did try return new Promise(reject, resolve) { }); manual wrap. It is simply a function that uses promises itself (successfully) to get data.
Update 1
stuff.doSomeReallyLongAndBoringFunction() is too big to post directly, but it does something like this:-
var Promise = require('bluebird'),
rp = require('request-promise');
module.exports = {
doSomeReallyLongAndBoringFunction: function() {
var p = Promise.resolve();
p = p.then(function() {
return db.find() //etc. etc.
});
p.then(function() {
rp(options).then(function(response){
//get some data from remote location
}).then(function(dataFromService) {
//do some jiggery pokery with said data
var marshalledData = dataFromService;
db.something.create({
Field: 'something'
}).exec(function(err, saved) {
return marshalledData;
});
});
}).catch(function(err) {
});
};
};
Update 2
Thank you Justin for your help. Here is the actual code, perhaps this may help?
Promise.resolve()
.then(function() {
if(typeof utils.intTryParse(place) !== 'number') {
return foursquare.createPlaceFromFoursquare(sso, place, request, reply);
} else {
return { Place: { PlaceId: place }};
}
}).then(function(placeObj) {
console.log('Place set as', placeObj); //always returns undefined, despite function actually completing after async op...
});

If your doSomeReallyLongAndBoringFunction is really running asynchronously, then it doesn't make sense to run it the way you have setup.
Edit - Here's a simple explanation of the way your code looks to be running vs a refactored version. It's been simplified , so you'll need to fill in the relevant sections with your actual implementation.
var Promise = require('bluebird');
function myAsync() {
setTimeout(function(){
return 'done sleeping';
}, 2000);
};
//The way your code is running
Promise.resolve()
.then(function(){
return 'hello';
})
.then(function(done){
console.log(done);
return myAsync(); //your error is here
})
.then(function(done){
console.log(done);
});
//refactored
Promise.resolve()
.then(function(){
return 'hello';
})
.then(function(done){
console.log(done);
return new Promise(function(resolve) {
setTimeout(function(){
resolve('done sleeping');
}, 2000);
});
})
.then(function(done){
console.log(done);
});

just for clarity, stuff.doSomeReallyLongAndBoringFunction() does not return a Promise itself.
And that's your problem. As it does something asynchronous and you want to get its result, it should return a promise. In fact, that's the case for every asynchronous function, especially then callbacks! It should be something like
module.exports = {
doSomeReallyLongAndBoringFunction: function() {
return db.find()
// ^^^^^^
.then(function() {
return rp(options).then(function(response){
// ^^^^^^
//get some data from remote location
}).then(function(dataFromService) {
//do some jiggery pokery with said data
var marshalledData = dataFromService;
return db.something.create({
// ^^^^^^
Field: 'something'
}).execAsyc();
});
}).catch(function(err) {
});
}
};
Your getSomething method has the same issues, and should look like this:
var createPlace = Promise.promisify(foursquare.createPlaceFromFoursquare);
module.exports = {
getSomething: function(request) {
var p;
if (typeof utils.intTryParse(place) !== 'number')
p = createPlace(sso, place, request); // this returns a promise!
else
p = Promise.resolve({Place: {PlaceId: place}});
return p.then(function(placeObj) {
// ^^^^^^
console.log('Place set as', placeObj);
});
}
};
See also these generic rules for promise development.

doSomeReallyLongAndBoringFunction needs to look like this:
doSomeReallyLongAndBoringFunction: function(param) {
var resolver = Promise.defer();
/*
* do some asynchronous task and when you are finished
* in the callback, do this:
*/
resolver.resolve(resultFromAsyncTask);
/*
*
*
*/
return resolver.promise;
}