Problem with making a simple JS XmlHttpRequest call

Question

Edit: Maybe I made the question more complex than it should. My questions is this: How do you make API calls to a server from JS.

I have to create a very simple client that makes GET and POST calls to our server and parses the returned XML. I am writing this in JavaScript, problem is I don't know how to program in JS (started to look into this just this morning)!

As n initial test, I am trying to ping to the Twitter API, here's the function that gets called when user enters the URL http://api.twitter.com/1/users/lookup.xml and hits the submit button:

function doRequest() {
    var req_url, req_type, body;
    req_url = document.getElementById('server_url').value;
    req_type = document.getElementById('request_type').value;   
    alert("Connecting to url: " + req_url + " with HTTP method: " + req_type);
    req = new XMLHttpRequest();
    req.open(req_type, req_url, false, "username", "passwd");// synchronous conn
    req.onreadystatechange=function() {
            if (req.readyState == 4) {
                    alert(req.status);
            }
    }
    req.send(null);
}

When I run this on FF, I get a

Access to restricted URI denied" code: "1012

error on Firebug. Stuff I googled suggested that this was a FF-specific problem so I switched to Chrome. Over there, the second alert comes up, but displays 0 as HTTP status code, which I found weird.

Can anyone spot what the problem is? People say this stuff is easier to use with JQuery but learning that on top of JS syntax is a bit too much now.

Only way to request another domain is using JOSNP: http://en.wikipedia.org/wiki/JSON#JSONP — Jarek, Apr 19 '10 at 21:51
You can't do cross domain file requests, but you can do cross domain data requests http://www.ibm.com/developerworks/library/wa-aj-jsonp1/ — Roman, Apr 19 '10 at 21:51
BTW, have you looked at how much jQuery abstracts away for you? http://api.jquery.com/jQuery.getJSON/ — Roman, Apr 19 '10 at 21:52

score 3 · Accepted Answer · answered Apr 19 '10 at 21:45

3

For security reasons, you cannot use AJAX to request a file from a different domain.

Since your Javascript isn't running on http://api.twitter.com, it cannot request files from http://api.twitter.com.

Instead, you can write server-side code on your domain to send you the file.

answered Apr 19 '10 at 21:45

SLaks

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What is the correct way to contact REST APIs using JS? The call I'm trying to make here is trivial to code in Java, I don't understand why it's so hard in JS. – recipriversexclusion Apr 19 '10 at 21:49
It's not a matter of difficulty, it's just [not allowed](http://en.wikipedia.org/wiki/Same_origin_policy). You have to use an Ajax-alternative request method, such as [JSONP](http://en.wikipedia.org/wiki/JSON#JSONP). – Jonathan Lonowski Apr 19 '10 at 22:01
@Jonathan and SLaks, maybe I'm misunderstanding, but what I'm trying to has nothing to do with accessing methods or files on a server, I'm just trying to send a GET request to the Twitter API. – recipriversexclusion Apr 19 '10 at 23:45
As far as the browser is concerned, there is no difference whatsoever between a file an a GET request to an API. – SLaks Apr 19 '10 at 23:58

Problem with making a simple JS XmlHttpRequest call

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