How to cast jQuery ajax calls to Bluebird promises without the deferred anit-pattern

Question

Right now I use promise.deferred in a core file. This allows me to resolve promises at a central location. I've been reading that I may be using an anti-pattern and I want to understand why it is bad.

so in my core.js file I have functions like this:

var getMyLocation = function(location) {    
    var promiseResolver = Promise.defer();

    $.get('some/rest/api/' + location)
        .then(function(reponse) {
            promiseResolver.resolve(response);
        )}
        .catch(function(error) {
            promiseResolver.reject(error);
        });

     return promiseResolver.promise;
}

And then in my getLocation.js file I have the following:

var core = require('core');
var location = core.getMyLocation('Petersburg')
    .then(function(response) {
        // do something with data
    }).catch(throw error);

After reading the Bluebird docs and many blog posts about the deferred anti-pattern I wonder if this pattern is practical. I could change this to the following:

core.js

var getMyLocation = function(location) {
    var jqXHR = $.get('some/rest/api/' + location);
    return Promise.resolve(jqXHR)
        .catch(TimeoutError, CancellationError, function(e) {
            jqXHR.abort();
            // Don't swallow it
            throw e;
        });

getLocation.js

var location = core.getMyLocation('Petersburg')
    .then(function(response) {
        // do something
    })
    .catch(function(error) {
        throw new Error();
    });

I guess I'm confused by what is the best way to have a central library that handles xhr requests using jquery for the calls, but Bluebird for the promises.

Answer 1

jQuery have promises implemented with their AJAX methods. In a nutshell, they are utilities that allow us to work with events that have completed or put them in queues or chain them – all of that good stuff. In our case, we need a “promise“. This allows us to interact with our AJAX requests – well outside our $.