fetch_iterator_promise.js

fetchSynchronous(fetchFactories) {
  // we have to fetch the data sequentially in order to avoid overloading the server
  // this array will hold the data from each response
  const data = [];

  // init a promise chain
  let p = Promise.resolve();

  // execute promises in a chain
  fetchFactories.forEach((fetchFactory) => {
    // fetchFactories will execute one at a time
    // pushing each response to an array that will contain all data
    // when all fetchFactories have been executed
    p = p.then(fetchFactory)
      .then((response) => {
        // place the data into an array
        data.push(response);
        // and then return the array to the promise chain
        return data;
      })
      .catch(err => Promise.reject(err));
  });

  // return the promise chain which will resolve to an array
  // containing the sequentially fetched data
  return p;
};