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CLI process lifecycle: output before an uncaught error is lost, process.exit(n) is reported as an uncaught error, process.exitCode / 'exit' are ignored, async errors exit 0 #48
Description
Test I ran
Eight two- or three-line scripts, each run with node <file> and slice run <file>, recording exit code, stdout and the first stderr line.
the eight scripts
a_uncaught_after_output.ts
console.log("line 1");
console.error("line 2 (stderr)");
throw new Error("boom");b_exit_0.ts
console.log("before exit");
process.exit(0);c_exit_3.ts
console.log("before exit");
process.exit(3);d_exit_5_in_timer.ts
console.log("a");
setTimeout(() => { console.log("b"); process.exit(5); }, 5);e_exitCode_and_exit_event.ts
process.on("exit", (code) => console.log("exit event, code=" + code));
process.exitCode = 7;
console.log("main done");f_unhandled_rejection.ts
Promise.reject(new Error("unhandled rejection"));
console.log("main done");g_throw_in_timer.ts
console.log("main done");
setTimeout(() => { throw new Error("thrown in timer"); }, 5);h_throw_in_async.ts
(async () => { await null; throw new Error("thrown in async fn"); })();
console.log("main done");Result
script | node v24.22.2: exit / stdout / stderr | slice v0.10.7: exit / stdout / stderr
a_uncaught_after_output.ts | 1 / line 1| / line 2 (stderr) | 1 / / Error: Uncaught Error: boom (unknown at :11:6)
b_exit_0.ts | 0 / before exit| / | 1 / / Error: Uncaught Error: process.exit(0)
c_exit_3.ts | 3 / before exit| / | 1 / / Error: Uncaught Error: process.exit(3)
d_exit_5_in_timer.ts | 5 / a|b| / | 0 / a|b| /
e_exitCode_and_exit_event.ts | 7 / main done|exit event, code=7| / | 0 / main done| /
f_unhandled_rejection.ts | 1 / main done| / Error: unhandled rejection | 0 / main done| /
g_throw_in_timer.ts | 1 / main done| / Error: thrown in timer | 0 / main done| /
h_throw_in_async.ts | 1 / main done| / Error: thrown in async fn | 0 / main done| /
(| marks a newline in stdout.) The .cas and slice compile standalone forms of scripts a and b behave the same as slice run.
What is wrong
| # | Behaviour on Slice | Expected |
|---|---|---|
| a | Everything written to stdout and stderr before an uncaught exception is discarded | Output written before the throw is kept |
| b, c | Top-level process.exit(0) / process.exit(3) exit with code 1, print Error: Uncaught Error: process.exit(N) and drop prior stdout |
Exit with code N, keep stdout, print nothing |
| d | process.exit(5) inside a timer callback exits with code 0 |
Exit code 5 |
| e | process.exitCode = 7 is ignored (exit 0) and the 'exit' listener never runs |
Exit code 7, listener runs |
| f, h | An unhandled promise rejection / an error thrown in an async function exits 0 with no message | Non-zero exit and the error on stderr |
| g | An error thrown inside a setTimeout callback exits 0 with no message |
Non-zero exit and the error on stderr |
Rows f–h mean a failing script can report success to a shell, CI job or child_process caller. docs/general/COMPATIBILITY.md lists process.exitCode, process.exit(code) and process.on as part of the supported process surface.
Environment
- Slice
v0.10.7, commitea7c70c, built withcargo +1.96.0 build --release --locked --bin slice - Reference: Node.js
v24.22.2(same script, same machine) - Ubuntu 26.04, Linux 7.0, x86_64
- Scripts a, b, e and f give the same result on the
v0.10.5tag, so this is not a regression in 0.10.6/0.10.7.
Activity
siktec-lab commentedon Nov 11, 2026
Fixed in PR #65 (
v0.10.9):__slice_process_exit(code)termination unwind (PanicError) soprocess.exit(code)insidetry / catch, Promises, and microtasks halts JS execution immediately and runsprocess.on("exit")listeners once.HostHooks::promise_rejection_trackerto track unhandled Promise rejections and either invokeprocess.on("unhandledRejection")or exit with code1(Uncaught (in promise)).process.exitCode,process.on("beforeExit"), andprocess.on("uncaughtException")/uncaughtExceptionMonitorsupport gated behind a zero-overheadDIRTY_PROCESSbitmask.