@rollup/plugin-commonjs: circular require receives undefined instead of {} before module.exports = #2042

• Rollup Plugin Name: @rollup/plugin-commonjs
• Rollup Plugin Version: 29.0.3
• Rollup Version: 4.68.0
• Operating System (or Browser): macOS 26.3 (Darwin 25.3.0 arm64)
• Node Version: v24.14.1
• Link to reproduction (⚠️ read below): https://gist.github.com/trackoor/7babb5ba8d1ed1d136b417eb320a50fe

Expected Behavior

When a CommonJS module with a top-level module.exports = ... assignment is required back in a circular dependency before that assignment executes, require() should return the module's initial {} exports object, matching Node's CommonJS semantics (printing { seenByB: 'object' } in the reproduction below). Similarly, top-level this before module.exports = ... should refer to that initial {} object.

Actual Behavior

A module with a top-level module.exports = ... assignment and no other module or exports references leaves its exports variable uninitialized (var a;) until the assignment executes. If another module requires it back in a cycle before that assignment runs, require() returns undefined instead of {} (printing { seenByB: 'undefined' } in the reproduction below).

The same uninitialized var also causes top-level this accesses before module.exports = ... (e.g. this.x = 1; module.exports = { y: 2 };) to throw TypeError: Cannot set properties of undefined.

Additional Information

// a.js
const b = require('./b.js');
module.exports = { seenByB: b.seen };

// b.js
const a = require('./a.js');
module.exports = { seen: typeof a };

// entry.js
console.log(require('./a.js'));

Bundling entry.js with @rollup/plugin-commonjs (default strictRequires: true or 'auto') and running the output prints { seenByB: 'undefined' }, whereas running node entry.js directly prints { seenByB: 'object' }.

Credit: https://ucsbplse.github.io/