René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`require('#x')` subpath imports fail with MODULE_NOT_FOUND under `--experimental-package-map`","articleBody":"### Version\n\nv26.10.0 (also v26.8.1)\n\n### Platform\n\n```text\nMicrosoft Windows NT 10.0.26100.0 x64\n, package maps\n```\n\n### Subsystem\n\nmodule, package maps\n\n### What steps will reproduce the bug?\n\nA CommonJS module cannot `require()` one of its own package's `\"imports\"` entries when a package map is active. ESM `import` of the same specifier works.\n\n```text\npkg/package.json   {\"name\":\"pkg\",\"version\":\"1.0.0\",\"imports\":{\"#*\":\"./src/*\"},\"main\":\"./index.cjs\"}\npkg/index.cjs      module.exports = require('#util.cjs');\npkg/src/util.cjs   module.exports = 'ok';\napp/package.json   {\"type\":\"module\"}\napp/a.cjs          console.log(require('pkg'));\nmap.json           {\"packages\":{\"app\":{\"url\":\"./app\",\"dependencies\":{\"pkg\":\"pkg\"}},\"pkg\":{\"url\":\"./pkg\",\"dependencies\":{}}}}\n```\n\n```console\n$ node --experimental-package-map=map.json app/a.cjs\nError: Cannot find module '#util.cjs'\n```\n\n### How often does it reproduce? Is there a required condition?\n\nAlways, when `--experimental-package-map` is set and a CommonJS module requires a `#` specifier.\n\n### What is the expected behavior? Why is that the expected behavior?\n\n`ok` is printed, as it is without the flag.\n\nThe `require()` algorithm in [modules.md](https://github.com/nodejs/node/blob/c89ec290f0f82f544e39e6e5f2eab3b6de2c1cca/doc/api/modules.md?plain=1#L342-L358) runs `LOAD_PACKAGE_IMPORTS` (step 4) and `LOAD_PACKAGE_SELF` (step 5) before `LOAD_PACKAGE_MAP` (step 6). The ESM resolver also sends `#` specifiers to [`packageImportsResolve`](https://github.com/nodejs/node/blob/c89ec290f0f82f544e39e6e5f2eab3b6de2c1cca/lib/internal/modules/esm/resolve.js#L828-L829) and asks the map only in [`packageResolve`](https://github.com/nodejs/node/blob/c89ec290f0f82f544e39e6e5f2eab3b6de2c1cca/lib/internal/modules/esm/resolve.js#L737-L740).\n\n### What do you see instead?\n\n```console\nError: Cannot find module '#util.cjs'\n  code: 'MODULE_NOT_FOUND'\n```\n\n### Additional information\n\nCause, in `lib/internal/modules/cjs/loader.js` (main at c89ec290f0):\n\n* [`Module._resolveFilename`](https://github.com/nodejs/node/blob/c89ec290f0f82f544e39e6e5f2eab3b6de2c1cca/lib/internal/modules/cjs/loader.js#L1526-L1531) calls `tryPackageMapResolveCJS` for every request that is not relative and not absolute. `#` requests are included.\n* [`tryPackageMapResolveCJS`](https://github.com/nodejs/node/blob/c89ec290f0f82f544e39e6e5f2eab3b6de2c1cca/lib/internal/modules/cjs/loader.js#L697-L712) throws MODULE_NOT_FOUND when the map has no entry for the request.\n* The [`#` imports block](https://github.com/nodejs/node/blob/c89ec290f0f82f544e39e6e5f2eab3b6de2c1cca/lib/internal/modules/cjs/loader.js#L1567-L1573) is never reached.\n\nSuggested fix: do the map lookup after the `#` imports step (and after `trySelf`), as the documented algorithm does, or skip the lookup for requests that start with `#`.\n\nPublished packages that use `\"imports\"` from CommonJS fail to load under a package map. For example, dependency-cruiser 18.2.0 has `require(\"#utl/try-require.cjs\")` in `src/extract/transpile/vue-template-wrap.cjs`. I found it through pnpm's `nodeExperimentalPackageMap` setting.\n\nThis was triaged using Opus 5.5 but verified by me to the best of my ability and filed by myself.","author":{"url":"https://github.com/christopher-buss","@type":"Person","name":"christopher-buss"},"datePublished":"2026-10-06T18:04:47Z","url":"https://github.com/nodejs/node/issues/66562"}