fix(mongo): fix support for deno by handling `TypedArray` when cloning by alexandre-abrioux · Pull Request #7258 · mikro-orm/mikro-orm

alexandre-abrioux · 2026-03-07T13:18:36Z

This PR fixes the usage of @mikro-orm/mongodb with Deno.

Issue

Using the newly added reproduction test case in tests/deno/mongodb.test.ts, and running it with no additional code change results in the following error:

> deno run --allow-read --allow-write --allow-env --allow-net --allow-sys --node-modules-dir=manual tests/deno/mongodb.test.ts
error: Uncaught (in promise) TypeError: this is not a typed array.
    at Uint8Array.values (<anonymous>)
    at Array.from (<anonymous>)
    at Object.toHex (file:///.../mikro-orm/node_modules/bson/lib/bson.cjs:481:22)
    at ObjectId.toHexString (file:///.../mikro-orm/node_modules/bson/lib/bson.cjs:2672:37)
    at eval (eval at createFunction (file:///.../mikro-orm/packages/core/src/utils/Utils.ts:900:14), <anonymous>:13:68)
    at ChangeSetComputer.computePayload (file:///.../mikro-orm/packages/core/src/unit-of-work/ChangeSetComputer.ts:145:20)
    at ChangeSetComputer.computeChangeSet (file:///.../mikro-orm/packages/core/src/unit-of-work/ChangeSetComputer.ts:61:56)
    at UnitOfWork.findNewEntities (file:///.../mikro-orm/packages/core/src/unit-of-work/UnitOfWork.ts:780:46)
    at UnitOfWork.computeChangeSets (file:///.../mikro-orm/packages/core/src/unit-of-work/UnitOfWork.ts:634:12)
    at UnitOfWork.doCommit (file:///.../mikro-orm/packages/core/src/unit-of-work/UnitOfWork.ts:514:12)

Investigation

Why is this bug appearing with Deno? The behavior is different because of this line of code in the bson package:

with Node.js, Buffer.prototype?._isBuffer is undefined ; so ByteUtils is using nodeJsByteUtils
with Deno, Buffer.prototype?._isBuffer is true ; so ByteUtils is using webByteUtils

The content of the fromHex method is different in both implementations:

With nodeJsByteUtils, it uses Buffer.from
with webByteUtils, it uses Uint8Array.from

The issue is that our clone function in packages/core/src/utils/clone.ts does not handle cloning of Uint8Array properly.

For instance, whit the following Uint8Array array:

Uint8Array(12) [
  105, 172, 10
]

Cloning it with our util function will result in:

Uint8Array {
  "0": 105,
  "1": 172,
  "2": 10
}

Fix

In this PR, we add proper support for cloning all TypedArray subtypes.

alexandre-abrioux · 2026-03-07T13:21:47Z

packages/core/src/utils/clone.ts

  return null;
 }

+const TypedArray = Object.getPrototypeOf(Uint8Array);


We can retrieve the TypedArray prototype by getting the prototype of any TypedArray subtype, like Uint8Array (see MDN).

codecov · 2026-03-07T13:21:51Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.68%. Comparing base (cc4b022) to head (9bed5af).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7258   +/-   ##
=======================================
  Coverage   99.68%   99.68%           
=======================================
  Files         261      261           
  Lines       25064    25068    +4     
  Branches     6967     6969    +2     
=======================================
+ Hits        24984    24988    +4     
  Misses         77       77           
  Partials        3        3

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B4nan · 2026-03-07T13:32:24Z

huh, did I forget to add formatting check to the CI?

please run yarn format

edit: and of course, thanks!

alexandre-abrioux · 2026-03-07T13:56:41Z

@B4nan Sorry I missed that! Done ✅

I've also added CI support for the new Deno test. I've tried to make it as light as possible by only pulling and starting the mongo service.

Thanks for the review!

B4nan

thanks again!

B4nan · 2026-03-07T17:56:00Z

packages/core/src/utils/clone.ts

      parent.copy(child as Buffer);
      return child;
+    } else if (parent instanceof TypedArray) {
+      child = parent.copyWithin(0);


claude flags this as wrong, since it doesnt actually clone anything. his suggestion is this instead:

Suggested change

child = parent.copyWithin(0);

child = parent.slice();

i should have paid more attention to this, copyWithin mutates, it doesnt create a new copy, any reason you used that? will address this as part of #7256

You're right, my bad 😬 Sorry, I don't manipulate TypedArray often, so I was looking at a method to clone it and misunderstood the docs of copyWithin. Indeed, slice is more appropriate, thanks for catching it!

alexandre-abrioux commented Mar 7, 2026

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alexandre-abrioux force-pushed the deno-mongodb branch from a87364f to 5ede55c Compare March 7, 2026 13:26

alexandre-abrioux marked this pull request as ready for review March 7, 2026 13:33

alexandre-abrioux force-pushed the deno-mongodb branch 3 times, most recently from de9e679 to 2c75491 Compare March 7, 2026 13:44

fix(core/utils): clone should handle TypedArray

9bed5af

alexandre-abrioux force-pushed the deno-mongodb branch from 2c75491 to 9bed5af Compare March 7, 2026 13:50

B4nan approved these changes Mar 7, 2026

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B4nan changed the title ~~fix(core/utils): clone should handle TypedArray~~ fix(mongo): fix support for deno by handling TypedArray when cloning Mar 7, 2026

B4nan merged commit 17ec4f5 into mikro-orm:master Mar 7, 2026
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B4nan reviewed Mar 7, 2026

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fix(mongo): fix support for deno by handling `TypedArray` when cloning#7258

fix(mongo): fix support for deno by handling `TypedArray` when cloning#7258
B4nan merged 1 commit intomikro-orm:masterfrom
alexandre-abrioux:deno-mongodb

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