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REPL is evaluating new lines before finishing execution of previous ones #39387
Description
Version
16.4.2
Platform
Archlinux x86_64
Subsystem
No response
What steps will reproduce the bug?
run with: node --experimental-repl-await file.mjs
import { PassThrough } from 'stream';
import { start } from 'repl';
async function main() {
const { input, output } = start({
input: new PassThrough(),
output: new PassThrough(),
useGlobal: false,
});
const script = `const x = await new Promise((r) => setTimeout(() => r(1), 500));\nx;`;
input.write(script);
input.end();
await new Promise((r) => setTimeout(r, 1000));
output.end();
let res = '';
for await (const chunk of output) {
res += chunk;
}
console.log(res);
}
main();How often does it reproduce? Is there a required condition?
100%
What is the expected behavior?
New lines should be queued and processed only after previous lines have finished.
What do you see instead?
New lines are executed before previous lines have finished
Additional information
Debug output:
$ NODE_DEBUG='repl' node --experimental-repl-await file.mjs
REPL 14900: line "const x = await new Promise((r) => setTimeout(() => r(1), 500));"
REPL 14900: eval "const x = await new Promise((r) => setTimeout(() => r(1), 500));\n"
REPL 14900: line "x;"
REPL 14900: eval "x;\n"
REPL 14900: not recoverable, send to domain
REPL 14900: domain error
REPL 14900: finish null undefined
> Uncaught ReferenceError: x is not defined
> undefined
>Sync code is not affected, but I would consider that a side effect of the sync code blocking the event loop preventing new lines being processed rather than a proper pause.
There's: de848ac that used another pause logic, but got reverted due to broking multiline repl.
This issue shouldn't be a blocker for #34733, as pause logic should be correct without depending on the event loop being blocked.
Activity
guybedford commentedon Jul 14, 2021
@ejose19 do you have any suggestions re a possible fix for this?
ejose19 commentedon Jul 14, 2021
Also, it would be better if
pauselogic is handled outsideeval(can unpause when executingevalcallback), so consumers providing their ownevalfunction get this working "transparently".ejose19 commentedon Jul 14, 2021
I've did some tests
for await (let cmd of self) {, it worked for this particular issue but error messages were totally different and some tests were failing. I've also checkedreadlinefor any API that could be useful, and the closest was https://nodejs.org/api/readline.html#readline_rl_pause, but as stated in the description, there's no guarantee that it will immediately pause other events. No other ideas rn, but ideallyfinishshould be in charge of executing or allowing execution of the next line, so whenevalexecutes the callback, the next line can be safely processed.github-actions commentedon Jun 27, 2026
This issue has been marked as stale due to 210 days of inactivity.
It will be automatically closed in 30 days if no further activity occurs. If this is still relevant, please leave a comment or update it to keep it open.
repl: use inspector over vm