René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Missing month in `Intl.DateTimeFormat` output when using `calendar: 'iso8601'` in Node v24.13.0 and later","articleBody":"### Version\n\nv24.15.0, v25.9.0\n\n### Platform\n\n```text\nDarwin Jasons-MacBook-Pro-2.local 25.4.0 Darwin Kernel Version 25.4.0: Thu Mar 19 19:30:44 PDT 2026; root:xnu-12377.101.15~1/RELEASE_ARM64_T6000 arm64\n```\n\n### Subsystem\n\n_No response_\n\n### What steps will reproduce the bug?\n\nRun the following code using Node.js **24.13.0 or later**:\n\n```js\nconst dtfWithIsoCalendar = new Intl.DateTimeFormat('en-US', {\n    dateStyle: 'full',\n    timeStyle: 'long',\n    timeZone: 'UTC',\n    calendar: 'iso8601'\n});\n\nconst date = new Date('2024-09-09T08:00:00Z');\n\nconsole.log(dtfWithIsoCalendar.format(date));\n```\n\n\n\n\n\n\n\n### How often does it reproduce? Is there a required condition?\n\nThe issue can be consistently reproduced under the following conditions:\n- Node.js version **24.13.0 or later**\n- Using `Intl.DateTimeFormat` with `calendar: 'iso8601'`\n\nThe issue does **not** reproduce:\n- On Node.js version **24.12.0 and earlier**\n- When using the default calendar (`'gregory'`) instead of `'iso8601'`\n\n### What is the expected behavior? Why is that the expected behavior?\n\nExpected output:\n\n```\n2024 September 9, Monday at 08:00:00 AM UTC\n```\n\nThe `format()` output should include the month \"September\".\n\n### What do you see instead?\n\nActual output (month is missing):\n\n```\n2024  9, Monday at 08:00:00 AM UTC\n```\n\n### Additional information\n\n_No response_","author":{"url":"https://github.com/jasongerbes-vista","@type":"Person","name":"jasongerbes-vista"},"datePublished":"2026-04-29T23:05:19.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/63041/node/issues/63041"}