Minimal Ajax XHR GET

minimal-ajax.js

  (function(url, cb) {

    var req = new XMLHttpRequest();
    req.onreadystatechange = function() {
      var err, res;
      if (req.readyState === 4) {
        if (req.status >= 200 && req.status < 300) {
          try {
            res = JSON.parse(req.responseText);
          } catch (e) {
            err = e && e.message || e;
          }
        } else {
          err = req.statusText || req.status;
        }
      }
      cb(err, res);
    }
    req.open("GET", url);
    req.send();

  })("https://example.com/index.json", function(err, res) {
    if (err) console.error(err);
    // do something
  });