Strange Behavior when using jQuery/asp.net WebApi - asp.net

Question

I have 2 Web API Projects:
Api1 is a testing-Environment for the JavaScript Front-End, but has a API
Back-end(the default ValuesController), also for testing.
Api2 is the "true" Back-end, from which the Experimental JavaScript UI schould pull Data. For Testing, i use the default ValuesController here too, because, i want to have the same Output.
Status Quo
The Api1-UI can query the Data from the ValuesController of the own API
The Api2 returns the Correct Data(tested in Firefox and with Fiddler)
The Code
JavaScript Client:
var _load = function (url) {
$.ajax({
url: url,
method: 'GET',
accepts: "application/json; charset=utf-8",
success: function (data) {
alert("Success: " + data);
},
error: function (data) {
alert("Error :" + data);
}
});
};
WebApi Controller method:
public IEnumerable<string> Get()
{
return new string[] { "value1", "value2" };
}
Problem
The JavaScript UI of the experimental Front-End is not able to display, or even receive, the data from the API 2, which is, according to Fiddler, sent correct.
My first thought was, I am using the wrong Method, but i tried $.getJSON and $.ajax. But i always end up with an error. It just says statusText= "Error"
I don't get, why it can display Data from the own ApiController, but not from the "External"...
Thanks for any Help/Suggestions

Answer 1

You seem to be accessing data from X from a different domain Y using ajax. This seems to be a classic cross domain access issue.
You need to set Access-Control-Allow-Origin to value " * " in your response header.
Response.Headers.Add("Access-Control-Allow-Origin", "*")
There various ways you can solve this
defining this header in IIS
using a actionfilter attribute like below
FilterAttribute
public class AllowCrossSiteJsonAttribute : ActionFilterAttribute
{
public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
{
if (actionExecutedContext.Response != null)
actionExecutedContext.Response.Headers.Add("Access-Control-Allow-Origin", "*");
base.OnActionExecuted(actionExecutedContext);
}
}
Using Attribute on Controller Action
[AllowCrossSiteJson]
public Result Get(int id)
{
//return appropriate result
}