var makeRequest = function(url, method) {
  // Create the XHR request
  var request = new XMLHttpRequest();

  // Return it as a Promise
  return new Promise(function(resolve, reject) {
    // Setup our listener to process compeleted requests
    request.onreadystatechange = function() {
      // Only run if the request is complete
      if (request.readyState !== 4) return;

      // Process the response
      if (request.status >= 200 && request.status < 300) {
        // If successful
        resolve(request);
      } else {
        // If failed
        reject(request);
      }
    };

    // Setup our HTTP request
    request.open(method, url, true);

    // Send the request
    request.send();
  });
};
let inputRub = document.getElementById("rub"),
  inputUsd = document.getElementById("usd");

function getCurrency(){
  let data = JSON.parse(request.response),
  usd = data.usd;
  return usd;
}

function converRublesToUsd() {
  inputRub.addEventListener("input", () => {
    inputUsd.value = inputRub.value ;
  });
}

function showWhoopsMessage() {
  inputUsd.value = "Something went wrong";
}

makeRequest("http://localhost:5500/js/db.json", "GET")
  .then(converRublesToUsd)
  .catch(showWhoopsMessage);