JS: Function with callback.

callback.js

function httpGet(url, callback) {
  var xmlHttp = new XMLHttpRequest();

  xmlHttp.onreadystatechange = function() {
    if (xmlHttp.readyState == 4 && xmlHttp.status == 200) {
      callback.call(this, JSON.parse(xmlHttp.responseText));
    }
  };

  xmlHttp.open("GET", url, false);
  xmlHttp.send();
}

httpGet('/feedbacks/delete_me', function(response) {
  console.log(response);
});