A function that does XMLHttpRequest handling and such

XMLHttpRequestFUNC.js

function XMLHttpRequestFUNC(method, url, async) {
  var xhr = new XMLHttpRequest();
  xhr.onreadystatechange = function() {
    if (xhr.readyState == 4 && xhr.status == 200) {
      console.log(xhr.response);
      return;
    }
  };
  xhr.open(method, url, async); // arguments[#]
  // xhr.setRequestHeader("User-Agent", "https://youngchief-btw.github.io/"); // header, value
  xhr.getAllResponseHeaders();
  xhr.send();
}

// Usage Example:
// XMLHttpRequestFUNC("GET", "https://www.uuidgenerator.net/api/version4/500", true);