René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"assert.deepStrictEqual / util.isDeepStrictEqual throw TypeError on Maps with null keys","articleBody":"### Version\n\nv24.13.1, v26.4.0 (reproduced on both)\n\n### Platform\n\n```text\nDarwin 24.x arm64 (also reproduces on Linux x64)\n```\n\n### Subsystem\n\nassert, util\n\n### What steps will reproduce the bug?\n\n```js\nconst { isDeepStrictEqual } = require('node:util');\n\nisDeepStrictEqual(\n  new Map([[null, { v: 1 }], [{ a: 1 }, 1]]),\n  new Map([[{ b: 2 }, { v: 1 }], [{ a: 1 }, 1]])\n);\n// TypeError: Cannot read properties of null (reading 'constructor')\n```\n\nThe same input crashes `assert.deepStrictEqual` and `assert.notDeepStrictEqual`\nwith the same TypeError (instead of an `AssertionError` / clean pass).\n\nThe triggering shape: one Map has a `null` key whose value is an object, the\nother Map lacks a `null` key but contains an object key with a deeply-equal\nvalue, plus at least one additional entry. Simpler null-key cases (primitive\nvalues, or no other entries) return correctly, so the crash is in the\nsecond-pass unordered key matching.\n\n### How often does it reproduce? Is there a required condition?\n\nDeterministic.\n\n### What is the expected behavior? Why is that the expected behavior?\n\n`isDeepStrictEqual` returns `false`; `assert.deepStrictEqual` throws\n`AssertionError`; `assert.notDeepStrictEqual` passes. A comparison predicate\nshould never throw a `TypeError` on valid inputs.\n\n### What do you see instead?\n\n```text\nTypeError: Cannot read properties of null (reading 'constructor')\n```\n\n### Additional information\n\nLikely cause: in the fallback pass that pairs non-identical Map keys by deep\nequality, keys with `typeof key === 'object'` are collected for pairwise\ncomparison, and `null` (also `typeof 'object'`) reaches a code path that reads\n`key.constructor` without a null guard.\n\nFound by differential fuzzing of deep-equality implementations; happy to\nprovide more failing inputs (they all share the shape above).\n","author":{"url":"https://github.com/XyraSinclair","@type":"Person","name":"XyraSinclair"},"datePublished":"2026-07-11T23:26:24.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/64433/node/issues/64433"}