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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"require(esm) inside a module.register() hook module fails with ERR_INTERNAL_ASSERTION in 26.12.0","articleBody":"### Version\n\nv26.12.0 (works on v26.11.1 and v26.10.0)\n\n### Platform\n\n```text\nLinux x64\n```\n\n### Subsystem\n\nesm, module\n\n### What steps will reproduce the bug?\n\n```js\n// repro.mjs\nimport { mkdtempSync, writeFileSync } from 'node:fs'\nimport { register } from 'node:module'\nimport { tmpdir } from 'node:os'\nimport { join } from 'node:path'\n\n// Any ES module with at least one import (one without imports works)\nconst esm = join(mkdtempSync(join(tmpdir(), 'require-esm-')), 'esm.mjs')\nwriteFileSync(esm, \"import 'node:fs'\\n\")\n\n// The hook module defines no hooks: loading it in the hooks thread is enough\nconst hooks = `\nimport { createRequire } from 'node:module'\ncreateRequire(${JSON.stringify(esm)})(${JSON.stringify(esm)})\n`\n\nregister('data:text/javascript,' + encodeURIComponent(hooks))\nconsole.log('ok')\n```\n\n```sh\nnode repro.mjs\n```\n\n\n\n### How often does it reproduce? Is there a required condition?\n\nAlways. Required conditions:\n\n- The `require()` happens while loading a `module.register()` hook module (the hooks thread).\n- The required ES module has at least one import. With `export {}` instead, it prints `ok`.\n\nNo hooks need to be exported: the hook module defines none.\n\n\n### What is the expected behavior? Why is that the expected behavior?\n\n`ok` is printed, as on v26.11.1 and v26.10.0 (which only print the `module.register()`\ndeprecation warning).\n\n\n### What do you see instead?\n\n\n```\nError [ERR_INTERNAL_ASSERTION]: This is caused by either a bug in Node.js or incorrect usage of Node.js internals.\nPlease open an issue with this stack trace at https://github.com/nodejs/node/issues\n\n    at assert (node:internal/assert:11:11)\n    at ModuleJobSync.syncLink (node:internal/modules/esm/module_job:330:9)\n    at ModuleJobSync.link (node:internal/modules/esm/module_job:626:17)\n    at new ModuleJobSync (node:internal/modules/esm/module_job:616:26)\n    at ModuleLoader.importSyncForRequire (node:internal/modules/esm/loader:352:11)\n    at loadESMFromCJS (node:internal/modules/cjs/loader:1786:24)\n    at Module._compile (node:internal/modules/cjs/loader:1950:5)\n    at Object..js (node:internal/modules/cjs/loader:2108:10)\n    at Module.load (node:internal/modules/cjs/loader:1690:32)\n    at Module._load (node:internal/modules/cjs/loader:1480:12) {\n  code: 'ERR_INTERNAL_ASSERTION'\n}\n```\n\nThe failing assertion is `assert(!isPromise(job))` in `ModuleJobSync.syncLink()`: inside the\nhooks thread, `getOrCreateModuleJob()` returns a promise for the required module's dependency\nwhile the module is being linked synchronously for `require()`.\n\n\n### Additional information\n\nBisected between releases only: v26.11.1 works, v26.12.0 fails. v26.12.0 includes\n\"module: synchronously load most ES modules\" (#62530), which changed this code path; that PR is\nthe likely cause but the exact commit was not bisected.\n","author":{"url":"https://github.com/ivan-tymoshenko","@type":"Person","name":"ivan-tymoshenko"},"datePublished":"2026-10-15T15:15:51Z","url":"https://github.com/nodejs/node/issues/66767"}