ES6 Spawn

spawn.js

var spawn = function (generatorFn) {
  var continuer = function (verb, arg) {
        var r;

        try {
          r = generator[verb](arg);
        } catch (error) {
          return Promise.reject(error);
        }

        if (r.done) {
          return r.value;
        } else {
          return Promise
            .resolve(r.value)
            .then(fulfilled, rejected);
        }
      },
      generator = generatorFn(),
      fulfilled = continuer.bind(continuer, 'next'),
      rejected = continuer.bind(continuer, 'throw');
  
  return fulfilled();
};

var loadStory = function () {
  return spawn(function *() {
    try {
      let story = yield getJSON('story.json');

      addHtmlToPage(story.heading);

      for (let chapter of story.chapterURLs.map(getJSON)) {
        addHtmlToPage((yield chapter).html));
      }

      addTextToPage("All done");
    } catch (error) {
      addTextToPage("Argh, broken: " + error.message);
    }
    
    document.querySelector('.spinner').style.display = 'none';
  });
};