Function

rethrow will rethrow an error on the next turn of the JavaScript event loop in order to aid debugging.

Promises A+ specifies that any exceptions that occur with a promise must be caught by the promises implementation and bubbled to the last handler. For this reason, it is recommended that you always specify a second rejection handler function to then. However, rethrow will throw the exception outside of the promise, so it bubbles up to your console if in the browser, or domain/cause uncaught exception in Node. rethrow will also throw the error again so the error can be handled by the promise per the spec.

import { rethrow } from 'rsvp';

function throws(){
  throw new Error('Whoops!');
}

let promise = new Promise(function(resolve, reject){
  throws();
});

promise.catch(rethrow).then(function(){
  // Code here doesn't run because the promise became rejected due to an
  // error!
}, function (err){
  // handle the error here
});

The 'Whoops' error will be thrown on the next turn of the event loop and you can watch for it in your console. You can also handle it using a rejection handler given to .then or .catch on the returned promise.