Custom promise catch handling.

catch-proxy.js

// transforms a rejection into a custom-format.
const catchTransformer = (fn, catchMap) => fn().catch(err => Promise.reject(catchMap(err)));

// Example of code that we don't control. The rejection follows its own format (e.g. fetch api).
const doSomethingAsyncThatFails = () =>
  new Promise((resolve, reject) => {
    setTimeout(() => reject(new Error('failed')), 1000);    
  });


// transform un-owned promise rejection into our rejection format
const doSomethingAsyncWithCustomRejection = () =>
  catchTransformer(doSomethingAsyncThatFails, err => ({ id: '500', message: 'custom message' }));


doSomethingAsyncWithCustomRejection()
  .then(res => console.log('result', result))
  .catch(err => console.log('error', err));