index.js

var promise = getPromise('http://api.icndb.com/jokes/random')

promise.then(function(data) {
  console.log('Got data! Promise fulfilled.'); // 1st request finished

  // 2nd request
  return getPromise('http://api.icndb.com/jokes/random');
}).then(function(result) {
  console.log('the final result');
});

// or

var promise = getPromise('http://api.icndb.com/jokes/random')

promise.then(function(data) {
  console.log('Got data! Promise fulfilled.'); // 1st request finished

  // 2nd request
  return getPromise('http://api.icndb.com/jokes/random');
  
}, function(error) {
  console.log('Promise rejected.');
  console.log(error.message);
}).then(function(result) {
  console.log('the final result');
});

promise.js

function getPromise(url) {
  return  promise = new Promise(function(resolve, reject) {
    var request = new XMLHttpRequest();
 
    request.open('GET', url);
    request.onload = function() {
      if (request.status == 200) {
        resolve(request.response); // we got data here, so resolve the Promise
      } else {
        reject(Error(request.statusText)); // status is not 200 OK, so reject
      }
    };
 
    request.onerror = function() {
      reject(Error('Error fetching data.')); // error occurred, reject the  Promise
    };
 
    request.send(); //send the request
  });
 
  console.log('Asynchronous request made.');
}