defer + promises

deferred.js

const log = console.log.bind(console, '--> ');
const warn = console.warn.bind(console, '!!! ');

export default function deferred(fn) {
  return new Promise((res, rej) => {
    setTimeout(() => {
      try {
        res(fn());
      } catch (e) {
        rej(e);
      }
    }, 0);
  });
}

if (require.main === module) {
  log(1);
  deferred(() => 20).then(x => deferred(() => x * 2)).then(log);
  deferred(() => bogus).then(log, warn);
  log(3);
}

/**
 * Output:
 * -->  1
 * -->  3
 * !!!  [ReferenceError: bogus is not defined]
 * -->  40
 */