getUrl.js

/**
 * Get content from a URL (e.g. JavaScript) using RSVP promises
 */
var getUrl = function (url) {
    var xhr = new XMLHttpRequest();

    // @see https://github.com/tildeio/rsvp.js
    var promise = new RSVP.Promise();

    xhr.open('GET', url);

    xhr.onreadystatechange = function () {
        if (xhr.readyState === 4) {
            if (xhr.status === 200) {
                promise.resolve(xhr.responseText);
            } else {
                promise.reject(new Error(xhr.statusText));
            }
        }
    };

    xhr.send();

    return promise;
};

/**
 * getUrl usage with chained call backs
 */
getUrl(url).then(function (text) {

    // Do something with URL responseText
    return text;
}).catch (function (error) {
  
    // Handle errors
});