Compare Async / Promise / Callback hell javascript code examples of same end

Async - Promise - Callback hell .js

/**
 * fsExists promise
 * @param {string} fp - filepath to check exists
 * @returns {Promise} fsExists
 */
const fsExists = (fp) => new Promise(
  resolve => fs.access(fp, err => resolve(!err))
);

const filepath = path.resolve(__dirname, 'tmp/service-worker.js');
const compiler = webpack(webpackConfig());
const plugin = new SWPrecacheWebpackPlugin({filepath});

plugin.apply(compiler);


/* Callback hell version */
test.cb('#writeServiceWorker(comiler, config)', t => {
  t.plan(2);

  fs.access(
    filepath,
    shouldNotExist => {
      t.falsy(!shouldNotExist, 'service-worker should not exist');
      plugin.writeServiceWorker(compiler, plugin.options).then(() => {
        fs.access(
          filepath,
          shouldExist => {
            t.truthy(!shouldExist, 'service-worker should exist');
            t.end();
          },
        );
      });
    }
  );
});

/* Promise version */
test('#writeServiceWorker(comiler, config)', t => {
  t.plan(2);

  return fsExists(filepath)
    .then(shouldNotExist => {
      t.falsy(shouldNotExist, 'service-worker should not exist yet');
    })
    .then(() => plugin.writeServiceWorker(compiler, plugin.options))
    .then(() => fsExists(filepath))
    .then(shouldExist => {
      t.truthy(shouldExist, 'service-worker should exist');
    });
});

/* Async/await version */
test('#writeServiceWorker(comiler, config)', async t => {
  t.plan(2);

  t.falsy(await fsExists(filepath), 'service-worker should not exist yet');
  await plugin.writeServiceWorker(compiler, plugin.options);
  t.truthy(await fsExists(filepath), 'service-worker should exist');
});