json - XMLHttpRequest cannot load an URL with jQuery

Question

I'm trying to get some json data from a "remote" website. I run my web service on the 99000 port then, I launch my website on the 99001 port (http://localhost:99001/index.html).

I get the following message:

    XMLHttpRequest cannot load http://localhost:99000/Services.svc/ReturnPersons. Origin http://localhost:99001 is not allowed by Access-Control-Allow-Origin.

Even If I launch my web page as an HTML file, I get this:

    XMLHttpRequest cannot load http://localhost:99000/Services.svc/ReturnPersons.Origin null is not allowed by Access-Control-Allow-Origin.

The web service returns data. I try to catch the data items like this:

var url = "http://localhost:99000/Services.svc/ReturnPersons";
$.getJSON(url, function (data) {
success: readData(data)
});
function readData(data) {
    alert(data[0].FirstName);
}

And I'm trying to get this structure:

[{"FirstName":"Foo","LastName":"Bar"},{"Hello":"Foo","LastName":"World"}]

Do you know why I'm getting this error?

Answer 1

You can't do a XMLHttpRequest crossdomain, the only "option" would be a technique called JSONP, which comes down to this:

To start request: Add a new <script> tag with the remote url, and then make sure that remote url returns a valid javascript file that calls your callback function. Some services support this (and let you name your callback in a GET parameters).

The other easy way out, would be to create a "proxy" on your local server, which gets the remote request and then just "forwards" it back to your javascript.

edit/addition:

I see jQuery has built-in support for JSONP, by checking if the URL contains "callback=?" (where jQuery will replace ? with the actual callback method). But you'd still need to process that on the remote server to generate a valid response.