fix(runtime): display proper error when throwing in event handlers#32663
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bartlomieju merged 2 commits intomainfrom Mar 12, 2026
Merged
fix(runtime): display proper error when throwing in event handlers#32663bartlomieju merged 2 commits intomainfrom
bartlomieju merged 2 commits intomainfrom
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When throwing in `unload`, `beforeunload`, `load`, or process exit/beforeExit event handlers, Deno displayed "Uncaught null" instead of the actual error message and stack trace. The root cause: when an event listener throws, the JS-side `reportException` calls `op_dispatch_exception` which stores the real exception in `ExceptionState` and terminates execution. The Rust-side event dispatch functions then checked `tc_scope.exception()` which returned the termination exception (null), not the stored one. Using `exception_to_err` instead properly retrieves the dispatched exception. Closes #29087 Co-Authored-By: Claude Opus 4.6 <[email protected]>
Co-Authored-By: Claude Opus 4.6 <[email protected]>
kajukitli
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Mar 12, 2026
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lgtm
using exception_to_err() here is the right fix. these call sites were bypassing the existing dispatched-exception handling and going straight to tc_scope.exception(), so once termination had swapped in the null-ish termination exception they lost the real error.
the new tests for load / beforeunload / unload cover the browser-style event cases well.
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Summary
"Uncaught null"being displayed instead of the actual error when throwing inunload,beforeunload,load, or processexit/beforeExitevent handlersreportExceptionin JS callsop_dispatch_exceptionwhich stores the real exception inExceptionStateand terminates execution. The Rust-side dispatch functions then checkedtc_scope.exception()which returnednull(the termination exception) instead of the stored oneexception_to_errwhich properly checksExceptionStatefor a dispatched exception before falling back totc_scope.exception()Before:
After:
Closes #29087