Cross domain call from SharePoint

Crossdomain.js

'use strict';
var context = SP.ClientContext.get_current()

(function () {
    var request = new SP.WebRequestInfo();
	var response;
	
	$(document).ready(function () {
    request.set_url("http://services.odata.org/Northwind/Northwind.svc/Categories");
    request.set_method("GET");
	request.set_headers({ "Accept": "application/json;odata=verbose" });
    response = SP.WebProxy.invoke(context, request);
    document.getElementById("categories").innerHTML = "<P>Loading categories...</P>";
    context.executeQueryAsync(successHandler, errorHandler);			
	});
	
    function successHandler() {

        if (response.get_statusCode() == 200) {
            var categories;
            var output;

            categories = JSON.parse(response.get_body());

            output = "<UL>";
            for (var i = 0; i < categories.d.results.length; i++) {
                var categoryName;
                var description;
                categoryName = categories.d.results[i].CategoryName;
                description = categories.d.results[i].Description;
                output += "<LI>" + categoryName + ":&nbsp;" +
                    description + "</LI>";
            }
            output += "</UL>";
            document.getElementById("categories").innerHTML = output;
        }
        else {
            var errordesc;
            errordesc = "<P>Status code: " +
               response.get_statusCode() + "<br/>";
            errordesc += response.get_body();
            document.getElementById("categories").innerHTML = errordesc;
        }
    }

    function errorHandler() {
        document.getElementById("categories").innerHTML =
            response.get_body();
    }
})();