$.param()

Object.keys(data).map(function(k) {
    return encodeURIComponent(k) + '=' + encodeURIComponent(data[k])
}).join('&');

AJAX

var request = new XMLHttpRequest();
request.open('POST', '/my/url', true);
request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
request.send(data);


var request = new XMLHttpRequest();
request.open('GET', '/my/url', true);
request.onload = function() {
    if (request.status >= 200 && request.status < 400) {
        // Success!
        var resp = request.responseText;
    } else {
        // We reached our target server, but it returned an error
    }
};
request.onerror = function() {
  // There was a connection error of some sort
};
request.send();