Please help me understand Ajax request versus Backbone fetch() - ajax

Question

My app can currently hit our API with a standard JQuery Ajax GET request and get good data back. CORS has been properly implemented on the remote server as far as I can see. Here are the response headers:
company_client_envelope_id: 88764736-6654-22e4-br344-a1w2239a892d
access-control-allow-headers: X-Requested-With, Cookie, Set-Cookie, Accept, Access-Control
Allow-Credentials, Origin, Content-Type, Request-Id , X-Api-Version, X-Request-Id,Authorization, COMPANY_AUTH_WEB
access-control-expose-headers: Location
response-time: 55
request-id: 88764736-6654-22e4-br344-a1w2239a892d
company_api_version: 0.01.09
server: localhost
transfer-encoding: chunked
connection: close
access-control-allow-credentials: true
date: Sun, 09 Feb 2014 14:44:05 GMT
access-control-allow-origin: *
access-control-allow-methods: GET, POST
content-type: application/json
However, using Backbone and calling the same GET request by using fetch() causes the following CORS error:
No 'Access-Control-Allow-Origin' header is present on the requested resource.
I cannot figure out what the difference is. Both requests are running from localhost.
In the case of the AJAX query, the following is being sent as requested by the API guys:
headers: {
"accept":"application/json"
}
And in the case of the model and collection declaration I am sending the headers like so:
MyApp.someCollection = Backbone.Collection.extend(
{
model:MyApp.someModel,
headers: {
'Accept':'application/json',
'withCredentials': 'true'
},
url: MYCOMPANY_GLOBALS.API + '/endpoint'
});
and my fetch is simply:
someCollection.fetch();
===============================
Added in response to: #ddewaele
These are the headers from the network tab:
Request URL:http://api-blah.com:3000/
Request Headers CAUTION: Provisional headers are shown.
Accept:application/json
Cache-Control:no-cache
Origin:http://localhost
Pragma:no-cache
Referer:http://localhost/blah/blah/main.html
User-Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/32.0.1700.107Safari/537.36
There is no pre-flight or remote headers from the API server:
many thanks,
Wittner

Answer 1

I've recommended to you rewrite Backbone.sync method, because in your app you have some security field for example and other reason.
var oldBackboneSync = Backbone.sync;
// Override Backbone.Sync
Backbone.sync = function (method, model, options) {
if (method) {
if (options.data) {
// properly formats data for back-end to parse
options.data = JSON.stringify(options.data);
}
// transform all delete requests to application/json
options.contentType = 'application/json';
}
return oldBackboneSync.apply(this, [method, model, options]);
}
You can add different headers as you want.