fix: contain exceptions thrown by consumer onError callback - #13
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fail() runs as the terminal .catch of the serialized mount/reset chain. A consumer onError that threw would reject chainRef.current, producing an unhandled promise rejection and poisoning the chain so every subsequent mount/reset link was silently skipped — violating the documented invariant that a rejection never poisons the chain. Wrap the onError call in try/catch and route a callback exception to console.error so the diagnostic path can never become a new failure. Closes #9
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Summary
Fixes #9 — a consumer
onErrorcallback that throws escapes the wrapper as an unhandled promise rejection.fail()invokes the consumer'sonErrorunguarded. Sincefailis used as the terminal.catchhandler of the serialized mount/reset chain, a throw insideonErrorrejectschainRef.currentwith no downstream handler → unhandled promise rejection.It also has a consequence the original report didn't note: it poisons the serialized chain, violating the invariant the code documents (
// Every link ends in .catch so a rejection never poisons it.). OncechainRefis left rejected, subsequent mount/reset.thenlinks are silently skipped — later image changes are dropped and the consumer may be re-notified with a stale error.Fix
Wrap the
onErrorcall intry/catchand route a callback exception toconsole.error, so the diagnostic path can never become a new failure. The original error still reaches the consumer; callback exceptions can't escape.Severity note
This only triggers when the consumer's own
onErrorthrows (a misbehaving void callback), so it does not affect well-behaved callers. The fix is included because it is nearly free and makes the code's documented no-poison invariant actually hold.Test plan
npm test— 41 passing, including a new regression test ('contains a throwing onError without poisoning the chain') that asserts the throw is swallowed and the chain still resets afterward. Verified the test fails (unhandled rejection) with the guard removed.