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Drop extend CJS dependency - #273

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fuma-nama wants to merge 3 commits into
unifiedjs:mainfrom
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Drop extend CJS dependency#273
fuma-nama wants to merge 3 commits into
unifiedjs:mainfrom
fuma-nama:main

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@fuma-nama

@fuma-nama fuma-nama commented May 20, 2026 •
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Initial checklist

  • I read the support docs
  • I read the contributing guide
  • I agree to follow the code of conduct
  • I searched issues and discussions and couldn’t find anything or linked relevant results below
  • I made sure the docs are up to date
  • I included tests (or that’s not needed)

Description of changes

Removed the remaining CJS dependency extend, since unified itself is ESM-only, it would be great if all deps are also ESM so it doesn't need bundling to work in browser environments.

The extend package is being used as a deep merge utility, while its core functionality is being replaced by Object.assign(). I think a proper deep merge utility would do better, but extend has some behaviours that may differs from existing deep merge utilities, so I rewrote the original utility with modern ESM, shouldn't cause any breaking changes.

I had to lower the test coverage as some edge cases are not easily reached, let me know if this isn't desirable.

@github-actions github-actions Bot added 👋 phase/new Post is being triaged automatically 🤞 phase/open Post is being triaged manually and removed 👋 phase/new Post is being triaged automatically labels May 20, 2026
Murderlon
Murderlon reviewed May 20, 2026
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@Murderlon Murderlon left a comment

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Not up to me to decide whether this goes in. Knowing @wooorm, he really likes consistency. So that usually means using extend everywhere or nowhere, not just dropping in one package. Luckily it seems there are only two

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Comment thread lib/deep-merge.js
@fuma-nama

fuma-nama commented May 20, 2026 •
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Oops I didn't search in other repositories, I think that will need another PR, would like to hear some inputs from maintainers before doing that. extend doesn't actually merge data structures like Map & Set, there's better alternatives for deep merge utils.

@Murderlon

Murderlon commented May 20, 2026

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Taking a step back, wondering if we can use structuredClone, browser support is good, also in Node.js since 17.0.0 🤔

@fuma-nama

fuma-nama commented May 20, 2026

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I think some libraries might store functions in the settings object, I would prefer to not break anything when possible.

@wooorm

wooorm commented Jun 3, 2026

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Sorry but I don‘t think this is possible.

I tried structuredClone. It passed tests. It worked in several of the 100s of repos. Then in failed in some. Some things put functions on data.
There are lots of people writing their own plugins and doing all kinds of things.

This requires lots and lots of tests to have parity with extend.
At that point, put it in a new repo, share it with the world. Maybe then it can be used here.

See GH-263, GH-153

@wooorm wooorm closed this Jun 3, 2026
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@wooorm wooorm added the 👀 no/external This makes more sense somewhere else label Jun 3, 2026
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github-actions Bot commented Jun 3, 2026 •
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Hi team! Could you describe why this has been marked as external?

Thanks,
— bb

@github-actions github-actions Bot added 👎 phase/no Post cannot or will not be acted on and removed 🤞 phase/open Post is being triaged manually labels Jun 3, 2026
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@fuma-nama @Murderlon @wooorm