Unhandled rejection occurs when not chained

1. What version of bluebird is the issue happening on? 3.5.0
2. What platform and version? (For example Node.js 0.12 or Google Chrome 32) Chrome 58 - jsfiddle
3. Did this issue happen with earlier version of bluebird? Yes

It seems that chaining then, catch, and finally properly handles rejection, but when the calls to then, catch, and finally are not chained an unhandled rejection is thrown. I have a jsfiddle here.

var promiseCBs = [];

var promise1 = new Promise((resolve, reject) => {
	promiseCBs.push({resolve, reject});
});
var promise2 = new Promise((resolve, reject) => {
	promiseCBs.push({resolve, reject});
});

promise1.then(() => console.log('a'));
promise1.catch(() => console.log('b'));
promise1.finally(() => console.log('c'));

promise2.then(() => console.log('1'))
	.catch(() => console.log('2'))
  .finally(() => console.log('3'));

//unhandled rejection
promiseCBs[0].reject(new Error('rej0'));

//no unhandled rejection
promiseCBs[1].reject(new Error('rej1'));

[bstutsky]

Interesting, I didn’t realize this previously. Thanks for the knowledge!

[benjamingr]

Multicast semantics are fundamental to promises, this is part of the spec and you can create a model that only allows one continuation (in JS those are typically called “tasks”).

Multicast semantics are fundamental in the design of promises. In practice if promises were unicast then things like unhandled rejections and cancellation become a lot simpler at the expense of the end user.