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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"stream/iter: from() accepts async-only nested values from sync iterables","articleBody":"### Version\n\nmain\n\n### Platform\n\n```text\nmacOS 26.5.2\n```\n\n### Subsystem\n\nstream\n\n### What steps will reproduce the bug?\n\n```js\nimport { from, text } from 'node:stream/iter';\n\nasync function* asyncGenerator() {\n  yield 'data';\n}\n\ntry {\n  console.log(await text(from([asyncGenerator()])));\n} catch (error) {\n  console.log(`${error.name}: ${error.code ?? error.message}`);\n}\n```\n\n### How often does it reproduce? Is there a required condition?\n\nAlways\n\n### What is the expected behavior? Why is that the expected behavior?\n\n`from([asyncGenerator()])` should throw, because the outer source is a sync iterable and the nested value is async-only.\n\nSpec [§8.1](https://stream-iter.jasnell.me/#from-method) says that when `from()` treats a sync iterator as an async source, nested async iterables and `toAsyncStreamable` are unsupported. The sync-iterator fallback currently routes nested values through `normalizeAsyncValue()`, which accepts async iterables and `toAsyncStreamable`, so the nested async generator is consumed instead of rejected.\n\n\n### What do you see instead?\n\n```console\ndata\n```\n\n### Additional information\n\n_No response_","author":{"url":"https://github.com/trivikr","@type":"Person","name":"trivikr"},"datePublished":"2026-07-08T06:22:45.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/64351/node/issues/64351"}