Please clarify how throwing inside subscribe() works

[pastelmind]

Currently, subscribe() consumes errors thrown inside the callback:

// There is no way to catch this error, other than listening to the global
// 'unhandledrejection' event
subscribe(store, () => { throw new Error() })

// This will not throw
store.value = 1

This is because subscribe() does not handle rejections here:

valtio/src/vanilla.ts

Lines 378 to 383 in 26caa88

	promise = Promise.resolve().then(() => {
	promise = undefined
	if (isListenerActive) {
	callback(ops.splice(0))
	}
	})

If a synchronously subscribed callback throws, it does cause the offending mutation to throw. But it will also cause all subscribers registered after it to be skipped:

subscribe(store, () => { throw new Error() }, true);
subscribe(store, () => console.log('I am skipped'), true);
subscribe(store, () => console.log('So am I'));

assert.throws(() => {
  // This will throw
  store.value = 1
})

This is because all subscribers are invoked synchronously here:

valtio/src/vanilla.ts

Line 176 in 26caa88

listeners.forEach((listener) => listener(op, nextVersion))

I just want to know if this is intended. I don't care if it is fixed or kept this way. But it would be beneficial if this behavior is documented somewhere.

[dai-shi]

In the valtio mental model, you can't stop the mutation. subscribe is called to notify that the mutation happened after the mutation.

I think we should say, throwing in the subscription callbacks leads to an unexpected behavior.