Esimorp

Inside Out Promises.

^{_{The simplest, yet handy, resolvable and rejectable Promises for all developers use cases.}}

// The constructor callback is optional.
// If provided, it's exactly the same
// that you would pass to a new Promise.
const promise = new Esimorp();
 
// you can already use the instance
// just like any other Promise
promise
  .then(console.log)
  .catch(console.error);
 
// ... and whenever it happens ...
promise.resolve('kudos');

F.A.Q.

• can I promise.then().resolve() ? Nope, only the initial resolvable creator/owner can resolve it. No side effects at distance.
• can I safely pass around a promise.then() ? Absolutely, that just creates a new Promise copy that's not resolvable.
• how can I abort an operation ? It's up to you, but following there is an example.

function fetchy(url) {
 
  const p = new Esimorp();
  const xhr = new XMLHttpRequest();
 
  // derive from Esimorp
  // to avoid external resolution
  const out = p.then();
  // expose only abort, delegating to xhr
  out.abort = xhr.abort.bind(xhr);
 
  // resolve indirectly out through Esimorp p
  xhr.addEventListener('abort', e => p.reject(e));
  xhr.addEventListener('error', e => p.reject(e));
  xhr.addEventListener('load', e => p.resolve(xhr));
 
  // perform the operation
  xhr.open('get', url);
  xhr.send();
 
  // return the Promise with abort delegate
  return out;
}

• what else could I do with this ? You could create Promises with a timeout and resolve or reject them before.

const p = new Esimorp((res, rej) => {
  // reject in 5 seconds
  setTimeout(rej, 5000, 'timeout');
});
 
// but if resolved or rejected first is OK
setTimeout(() => p.resolve('OK'), 1000);

License

(C) 2017 Andrea Giammarchi, @WebReflection, MIT Style License.