TypeError: Expected CommonJS module to have a function wrapper. If you weren't messing around with Bun's internals, this is a bug in Bun #25398
Description
What version of Bun is running?
1.3.4
What platform is your computer?
Darwin 24.6.0 arm64 arm
What steps can reproduce the bug?
I originally found this issue with our NextJS Webpack build and bun would not be able to run it and I was able to create a very easy way to reproduce that passes with node and not in bun
cat > /tmp/bun-bug.js << 'REPRO'
// Minimal reproduction for Bun CommonJS loader bug
// Bug: "Expected CommonJS module to have a function wrapper"
//
// Works: node bun-bug.js
// Fails: bun run --bun bun-bug.js
//
// Root cause: In a Webpack-style CommonJS chunk with arrow function
// using BLOCK BODY (not expression body), the combination of:
// 1. Spread operator (...k)
// 2. Optional chaining + nullish coalescing to object literal (k?.x??{})
// inside a parenthesized expression causes Bun's CJS loader to fail.
//
// The expression body version =>(...) works fine.
// The block body version =>{...} fails.
exports.id=1,exports.ids=[1],exports.modules={1:(a,b,c)=>{let k={};({...k,a:k?.x??{}})}};
REPRO
echo "=== Minimal reproduction ==="
cat /tmp/bun-bug.js
echo ""
echo ""
echo "=== Testing ==="
echo "Node.js:"
node /tmp/bun-bug.js && echo " SUCCESS" || echo " FAILED"
echo ""
echo "Bun:"
bun run --bun /tmp/bun-bug.js 2>&1
Result:
=== Testing ===
Node.js:
SUCCESS
Bun:
6 | "use strict";
7 |
8 | //
9 | if (entry.instantiate)
10 | return entry.instantiate;
11 | var instantiatePromise = (async () => {
^
TypeError: Expected CommonJS module to have a function wrapper. If you weren't messing around with Bun's internals, this is a bug in Bun
What is the expected behavior?
Bun should be able to run this like NodeJS and result should be both success
What do you see instead?
TypeError: Expected CommonJS module to have a function wrapper. If you weren't messing around with Bun's internals, this is a bug in Bun
Additional information
No response