Error handling propagation issue

[totorototo]

there is something fishy in the chain saga, service, helper.

• services are in charge of:

  • formatting data to be passed to an helper,
  • calling helpers,
  • formatting returned data from that helper.

• helpers are generally based promise,

• this is exactly the same for services.

the problem is:

• what if an helper reject a promise?
• how is that handled in services?

PS:
Be aware of what is the return value of .then(): resolve or failure.
Considering the returned value of .then() in both case, we have done something wrong here!
🇿🇲

[totorototo]

As we discussed, something should be done using fp (Monads, ...).
see:
https://medium.com/javascript-scene/javascript-monads-made-simple-7856be57bfe8
http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html

{
const composeM = chainMethod => (...ms) => (
ms.reduce((f, g) => x => g(x)chainMethod)
);
const composePromises = composeM('then');
const label = 'API call composition';
// a => Promise(b)
const getUserById = id => id === 3 ?
Promise.resolve({ name: 'Kurt', role: 'Author' }) :
undefined
;
// b => Promise(c)
const hasPermission = ({ role }) => (
Promise.resolve(role === 'Author')
);
// Compose the functions (this works!)
const authUser = composePromises(hasPermission, getUserById);
authUser(3).then(trace(label)); // true
}