Promise chaining: Use result from previous promise in next then callback [duplicate]

Answer 1

In my opinion, the zen of promises is all about figuring out they're really just asynchronous values. If you start using them as such these problems become simpler in many cases. It's not a silver bullet but it sure does help:

In ES5:

var student = Student.find();
var helpRequest = student.then(HelpRequest.findByStudent);
Promise.all([student, helpRequest]).then(function(results){
    var student = results[0];
    var helpRequest = results[1];
    // access both here
});

In ES6, with all its features:

var student = Student.find();
var helpRequest = student.then(HelpRequest.findByStudent);
Promise.all([student, helpRequest]).then(([student, helpRequest]) => {
    // access both here
});

In another richer promise library (bluebird):

var student = Student.find();
var helpRequest = student.then(HelpRequest.findByStudent);
Promise.join(student, helpRequest, function(student, helpRequest){
    // access both here
});