Making requests with pure Javascript and promise (Fazendo requisições com Javascript puro e promise)

get.js

// promise example
function get(url) {
    // Return a new promise.
    return new Promise(function(resolve, reject) {
        // Do the usual XHR stuff
        var req = new XMLHttpRequest();
        req.open('GET', url);

        req.onload = function() {
            // This is called even on 404 etc
            // so check the status
            if (req.status == 200) {
                // Resolve the promise with the response text
                resolve(req.response);
            }
            else {
                // Otherwise reject with the status text
                // which will hopefully be a meaningful error
                reject(Error(req.statusText));
            }
        };

        // Handle network errors
        req.onerror = function() {
            reject(Error("Network Error"));
        };

        // Make the request
        req.send();
    });

} // promise example

// promise usage
get('https://jsonplaceholder.typicode.com/comments').then(function(response) {
    console.log("Success!", response); // show data
}, function(error) {
    console.error("Failed!", error); // show error
}); // promise usage