Question

using Backbone.js we have an application, in which on a certain occasion we need to send an ajax post to a clients webservice.

however, the content to be posted, is dynamic, and is decided by a certain array.

for each item in the array we need to go fetch a piece of data.

after assembling the data that aggregated object needs to be sent.

as of now, i have a synchronous approach, though i feel that this is not the best way.

var arrParams = [{id: 1, processed: false},{id: 7, processed: false},{id: 4, processed: false}];

function callback(data) {
    $.post()... // jquery ajax to post the data... }

function fetchData(arr, data, callback) {
    var currentId = _(arr).find(function(p){ return p.processed === false; }).id;  // getting the ID of the first param that has processed on false...

    // ajax call fetching the results for that parameter.
    $.ajax({
        url: 'http://mysuperwebservice.com',
        type: 'GET',
        dataType: 'json',
        data: {id: currentId},

        success: function(serviceData) {
            data[currentId] = serviceData;  // insert it into the data
            _(arr).find(function(p){ return p.id === currentId; }).processed = true; // set this param in the array to 'being processed'.
            // if more params not processed, call this function again, else continue to callback
            if(_(arr).any(function(p){ return p.processed === false }))
            {
                 fetchData(arr, data, callback);
            }
            else
            {
                callback(data);
            }
        },
        error: function(){ /* not important fr now, ... */ }
    }); 
}

fetchData(arrParams, {}, callback);

isn’t there a way to launch these calls asynchronous and execute the callback only when all results are in?

Answer 1

You have to use JQuery $.Deferred object to sync them. Look at this article Deferred Docs

You can use in this way:

$.when(
   $.ajax({ url : 'url1' }),
   $.ajax({ url : 'url2' }) // or even more calls
).done(done_callback).fail(fail_callback);