add import bytes #11657

styfle · 2025-09-15T02:23:05Z

Related to Road to Stage 2.7 tc39/proposal-import-bytes#13
Related to Import with type text, bytes, and URL #9444

At least two implementers are interested (and none opposed):
- Deno
- …
Tests are written and can be reviewed and commented upon at:
- …
Implementation bugs are filed:
- Chromium: …
- Gecko: …
- WebKit: …
- Deno (only for timers, structured clone, base64 utils, channel messaging, module resolution, web workers, and web storage): …
- Node.js (only for timers, structured clone, base64 utils, channel messaging, and module resolution): …
Corresponding HTML AAM & ARIA in HTML issues & PRs:
MDN issue is filed: …
The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

bakkot · 2025-09-15T02:40:33Z

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+   <li><p>Set <var>script</var>'s <span data-x="concept-script-parse-error">parse error</span> and
+   <span data-x="concept-script-error-to-rethrow">error to rethrow</span> to null.</p></li>
+
+   <li><p>Let <var>result</var> be a new <code>Uint8Array</code> object, in <var>settings</var>'s


You may want to use the creating an ArrayBufferView operation here (see e.g. the bytes() method on Response), although this does not allow you to specify specifically an immutable ArrayBuffer (yet?).

I don't think "backing bytes" is really a concept which exists anywhere.

Yeah, you might have to add a new argument for that or a separate operation.

I'm not sure I fully understand. Mind leaving a code suggestion?

This is the algorithm where creation of Uint8Array&friends is defined: https://github.com/whatwg/webidl/blob/a79e69ef7398ece546e526a1eebec977363c7304/index.bs#L9277-L9291

It needs to take a new parameter (I guess either a boolean or an enum like preserveResizability of https://tc39.es/proposal-immutable-arraybuffer/#sec-arraybuffercopyanddetach), propagate it to https://github.com/whatwg/webidl/blob/a79e69ef7398ece546e526a1eebec977363c7304/index.bs#L9252 and then call AllocateImmutableArrayBuffer (or ArrayBufferCopyAndDetach, depending on what is simpler) appropriately.

More precisely, as mentioned below, HTML should only be creating the ArrayBuffer, and then calling CreateBytesModule from the proposal.

So it's only the create an ArrayBuffer algorithm which needs updated with the new parameter, not the algorithm for creating new views like Uint8Array.

guybedford · 2025-09-15T02:33:28Z

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+    script</span> algorithm. Bytes module scripts represent binary data as Uint8Array backed by
+    an immutable ArrayBuffer.</p>


Might need to add references for both Uint8Array and Immutable Array Buffer here.

Fixed in b894372

guybedford · 2025-09-15T02:35:00Z

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+    <!--
+     This definition is not super-rigorous, but it doesn't need to be for now. If we ever start
+     testing if something is a Bytes module script in algorithms, instead of just referring to the
+     concept, then we should consider adding a type item to the module script struct.
+    -->


This definition is perfectly rigorous IMO - a bytes module script === the output of the creating a bytes module script steps. That's the definition.

Removed in 9647411

guybedford · 2025-09-15T02:37:27Z

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+   <li><p>Let <var>result</var> be a new <code>Uint8Array</code> object, in <var>settings</var>'s
+   <span data-x="environment settings object's realm">realm</span>, whose backing bytes are <var>bytes</var>.</p></li>


This needs to initialize and reference the immutable array buffer spec as well, as a direct reference to https://tc39.es/proposal-immutable-arraybuffer/#sec-arraybuffer-objects.

Also we only need to create the ArrayBuffer here that is immutable, the Uint8Array typed array view is added on the TC39 spec side.

I'm not sure I fully understand. Mind leaving a code suggestion?

I think we want to use Web IDL for this, similar to what the Encoding Standard does for instance. But to make the backing buffer immutable we'll have to make a small change to Web IDL to allow for that.

guybedford · 2025-09-15T02:44:54Z

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+   <li><p>Set <var>script</var>'s <span data-x="concept-script-record">record</span> to the result
+   of <span>CreateDefaultExportSyntheticModule</span>(<var>result</var>).</p></li>


Rather than calling CreatedefaultExportSyntheticModule directly, it would be good to reference the TC39 spec here by making this:

<li>Let <var>record</var> be CreateBytesModule(<var>immutableBytes</var>). <li>Set <var>script</var>'s record to <var>record</var>.</li>

sort of thing.

Where CreateBytesModule is then a reference to the https://tc39.es/proposal-import-bytes/ spec.

Added in 9828655

@guybedford @nicolo-ribaudo How's that look now?

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annevk · 2025-09-15T06:48:27Z

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+   <li><p>Set <var>script</var>'s <span data-x="concept-script-parse-error">parse error</span> and
+   <span data-x="concept-script-error-to-rethrow">error to rethrow</span> to null.</p></li>
+
+   <li><p>Let <var>result</var> be a new <code>Uint8Array</code> object, in <var>settings</var>'s


Yeah, you might have to add a new argument for that or a separate operation.

nicolo-ribaudo

To see how to link to a proposal, search for <ref>JSDYNAMICCODEBRANDCHECKS</ref> and [JSDYNAMICCODEBRANDCHECKS] through the document.

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annevk · 2025-09-17T06:38:14Z

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+
+   <p>The <span>bytes module script</span> will return a <code>Uint8Array</code> object containing
+   the raw bytes of the fetched resource. Unlike <span data-x="JSON module script">JSON module scripts</span>
+   which require a specific MIME type, bytes modules can be used to import binary data from any resource.</p>


Suggested change

which require a specific MIME type, bytes modules can be used to import binary data from any resource.

which require a specific MIME type, bytes module scripts can be used to import binary data from any resource.

annevk · 2025-09-17T06:38:50Z

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+    <p>A <span>module script</span> is a <dfn export>bytes module script</dfn> if its <span
+    data-x="concept-script-record">record</span> is a <span>Synthetic Module Record</span>, and it
+    was created via the <span data-x="creating a bytes module script">create a bytes module
+    script</span> algorithm. bytes module scripts represent binary data as <code>Uint8Array</code>


Suggested change

script algorithm. bytes module scripts represent binary data as <code>Uint8Array</code>

script algorithm. Bytes module scripts represent binary data as <code>Uint8Array</code>

annevk · 2025-09-17T06:40:16Z

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+
+   <li><p>Let <var>record</var> be <span>CreateBytesModule</span>(<var>immutableBytes</var>).</p></li>
+
+   <ref>JSIMPORTBYTES</ref>


This appears in the wrong place. It should usually appear just before a .

annevk · 2025-09-17T06:40:29Z

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+   <li><p>Return <var>script</var>.</p></li>
+  </ol>
+
+  <p>User agents that support JavaScript must also implement the <cite>Import Bytes</cite> proposal.


Indentation here is wrong.

annevk · 2025-09-17T06:41:01Z

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+  <p>User agents that support JavaScript must also implement the <cite>Import Bytes</cite> proposal.
+   The following terms are defined there, and used in this specification: <ref>JSIMPORTBYTES</ref></p>


This seems to be in the wrong place as well?

nicolo-ribaudo · 2025-09-17T15:34:27Z

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     <var>settingsObject</var>, <var>response</var>'s <span
     data-x="concept-response-url">URL</span>, and <var>options</var>.</p></li>

+     <li><p>If <var>moduleType</var> is "<code data-x="">bytes</code>", then set <var>moduleScript</var> to


I would move this before <li>Let <var>referrerPolicy</var> be the result of ..., and put the steps from it to the one that created the various other module scrips in an Else clause.

It's just an editorial suggestion to make it clear that those steps are useless for bytes module scripts, it does not actually affect behavior.

styfle mentioned this pull request Sep 15, 2025

Road to Stage 2.7 tc39/proposal-import-bytes#13

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bakkot reviewed Sep 15, 2025

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guybedford reviewed Sep 15, 2025

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annevk reviewed Sep 15, 2025

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nicolo-ribaudo reviewed Sep 15, 2025

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styfle added 5 commits September 16, 2025 19:54

add import bytes

f8b1b09

make "bytes module script" lowercase

183a2ce

add references to Uint8Array & ArrayBuffer

b894372

remove comment about super-rigorous

9647411

"stylesheets" => "style sheets"

e5b9757

styfle force-pushed the styfle/import-bytes branch from b6deeac to e5b9757 Compare September 17, 2025 00:05

add ref to JSIMPORTBYTES

9828655

annevk reviewed Sep 17, 2025

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nicolo-ribaudo reviewed Sep 17, 2025

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styfle mentioned this pull request Sep 23, 2025

Road to Stage 3 tc39/proposal-import-bytes#28

Open

15 tasks

		script</span> algorithm. Bytes module scripts represent binary data as Uint8Array backed by
		an immutable ArrayBuffer.</p>

		<li><p>Let <var>result</var> be a new <code>Uint8Array</code> object, in <var>settings</var>'s
		<span data-x="environment settings object's realm">realm</span>, whose backing bytes are <var>bytes</var>.</p></li>

		<li><p>Set <var>script</var>'s <span data-x="concept-script-record">record</span> to the result
		of <span>CreateDefaultExportSyntheticModule</span>(<var>result</var>).</p></li>

	which require a specific MIME type, bytes modules can be used to import binary data from any resource.</p>
	which require a specific MIME type, bytes module scripts can be used to import binary data from any resource.</p>


		<li><p>Let <var>record</var> be <span>CreateBytesModule</span>(<var>immutableBytes</var>).</p></li>

		<ref>JSIMPORTBYTES</ref>

		<p>User agents that support JavaScript must also implement the <cite>Import Bytes</cite> proposal.
		The following terms are defined there, and used in this specification: <ref>JSIMPORTBYTES</ref></p>

add import bytes #11657

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styfle commented Sep 15, 2025 •

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bakkot Sep 15, 2025 •

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nicolo-ribaudo Sep 17, 2025 •

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