emscripten-core/emscripten

Faulty assertion in node on .mjs files

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#17465 opened on Jul 18, 2022

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Description

It turns out that node will disable the global require function on foo.mjs - that is just not defined there, unlike for foo.js. I guess mjs files are modules and require is not supposed to be used there. This ends up a problem for us since we have an assertion on it:

https://github.com/emscripten-core/emscripten/blob/a3d8979b38d2f655f59b040bfd32f562ebc92d03/src/shell.js#L196-L198

Removing that assertion is necessary to run an .mjs file in node with -sASSERTIONS.

We should probably just remove it?

This happens on binaryen CI which will manually builds an .mjs file by concatenating the emcc output with some extra code.

Contributor guide

Tech stack
javascriptnodejs
Domain
clitooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
1
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Node.js module systemJavaScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
85
Research direction
The issue points to a specific assertion in shell.js (lines 196-198) that should be removed to allow .mjs files to run with sASSERTIONS in Node. The fix is straightforward: delete those lines. Before proceeding, check if any other code depends on the global require being defined. Also review the binaryen CI setup that triggered this issue to ensure compatibility.