unhandledrejection Promise

[tuchida]

https://developer.mozilla.org/en-US/docs/Web/API/Window/unhandledrejection_event

// Rhino
new Promise((resolve) => {
  print('resolve');
  resolve();
}).then(() => {
  p('');  // ReferenceError
});  // without .catch()

Rhino

resolve
[object Promise]

SpiderMonkey

Uncaught (in promise) ReferenceError: p is not defined
    <anonymous> debugger eval code:5
    promise callback* debugger eval code:4

node

ref. https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode

> (node:2889648) UnhandledPromiseRejectionWarning: ReferenceError: p is not defined
    at REPL6:5:3
    at processTicksAndRejections (internal/process/task_queues.js:95:5)

---

I think it will be difficult to debug without displaying an error or killing the process.

[gbrail]

Yes, I can see how that's supposed to result in an "uncatchable exception" actually and that Rhino should be throwing it. I can also see why existing test suites didn't catch it. Let's see what we can do.

[gbrail]

Fixed in #1007