[fix] UnhandledPromiseRejection crashes the koa server

[Matthewloughton]

Node 16: UnhandledPromiseRejection crashes the koa server

Node.js version: v16.17.0

Description: When an UnhandledPromiseRejection occurs, the koa server crashes. I noticed that it seems to be on Node 16.
How I found this was while using a library in which they inadvertently caused an UnhandledPromiseRejection. Fortunately I caught this issue before experiencing in prod!
I also sandbox tested with Express and it does the same.

Using node 14 does not exhibit this behaviour which leads me to believe it's related to Node 16

Code to reproduce

const app = new Koa();

app.use(ctx => {
    const prom = new Promise((resolve) => {
        throw 'Blah';
    });
});

app.listen(1234, () => {
    console.log('running on 1234')
});

[Matthewloughton]

Update:
Did some reading (I've been detached from node's versioning lately).

It seems like UnhandledPromiseRejection is strict by default now.

Run node with flag --unhandled-rejections=warn-with-error-code if you don't want it to crash

You guys can close this if you want. Your call

[Matthewloughton]

Another update:

You can write something like below to "catch" these unhandledRejections.

process.on('unhandledRejection', error => {
    console.log('handle the error');
});

Closing this issue. Hope my monologue helps someone!