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Add a textStream() method to the Body mixin #1862

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Add a textStream() method to the Body mixin #1862

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8a5f957
Add a textStream() method to the Body mixin
foolip Oct 2, 2025
b7d8c9d
Use the new 'set up a text decoder stream'
noamr May 20, 2026
91d8e00
Return an empty stream for null body
noamr May 21, 2026
3813986
unspecfmt
noamr May 21, 2026
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41 changes: 41 additions & 0 deletions fetch.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -8259,6 +8259,7 @@ interface mixin Body {
[NewObject] Promise<FormData> formData();
[NewObject] Promise<any> json();
[NewObject] Promise<USVString> text();
[NewObject] ReadableStream textStream();
};</pre>

<p class=note>Formats you would not want a network layer to be dependent upon, such as
Expand Down Expand Up @@ -8300,6 +8301,9 @@ due course.

<dt><code><var>requestOrResponse</var> . <a method for=Body>text</a>()</code>
<dd><p>Returns a promise fulfilled with <var>requestOrResponse</var>'s body as string.

<dt><code><var>requestOrResponse</var> . <a method for=Body>textStream</a>()</code>
<dd><p>Returns a {{ReadableStream}} with <var>requestOrResponse</var>'s body as string chunks.
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@annevk annevk May 21, 2026

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Suggested change
<dd><p>Returns a {{ReadableStream}} with <var>requestOrResponse</var>'s body as string chunks.
<dd><p>Returns a {{ReadableStream}} object with <var>requestOrResponse</var>'s body as string chunks.

</dl>

<hr>
Expand Down Expand Up @@ -8473,6 +8477,43 @@ of running <a for=Body>consume body</a> with <a>this</a> and <a>parse JSON from
of running <a for=Body>consume body</a> with <a>this</a> and <a>UTF-8 decode</a>.
</div>

<div algorithm>
<p>The <dfn method for=Body><code>textStream()</code></dfn> method steps are:</p>
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@annevk annevk Oct 2, 2025

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I think for the null case it'd be nicer to return an empty stream, similar to what text() does.

Another thing that's not entirely clear to me is whether piping ends up making the underlying stream unusable so that you can't invoke text() after textStream() for instance. (That's a property we want.)

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@foolip foolip Oct 2, 2025

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Ah, I didn't realize what text() does if this.body is null. I agree an empty stream would be better, code that doesn't consider this case would likely just work.

I thought this should behave like when you try to use both blob() and bytes(), or indeed call one of those twice. That throws a TypeError in the first step of https://fetch.spec.whatwg.org/#concept-body-consume-body.

Since it's not possible to call text() twice, should it really be possible to call text() after textStream()?

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@annevk annevk Oct 2, 2025

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It should not be possible.

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@foolip foolip Oct 2, 2025

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Good, that should be easy to achieve, even though the current spec text doesn't make clear what happens.

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@noamr noamr May 21, 2026

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Done. textStream now returns an empty stream for a null body.


<ol>
<li><p>If <span>this</span> is <a for=Body>unusable</a>, then throw a {{TypeError}}.

<li>
<p>If <span>this</span>'s <a for=Body>body</a> is null:

<ol>
<li><p>Let <var>emptyStream</var> be a new {{ReadableStream}} in <a>this</a>'s
<a>relevant realm</a>.

<li><p><a for="ReadableStream">Set up</a> <var>emptyStream</var>.

<li><p><a for="ReadableStream">Close</a> <var>emptyStream</var>.

<li><p>Return <var>emptyStream</var>.
</ol>

<li><p>Let <var>stream</var> be <a>this</a>'s <a for=Body>body</a>'s <a for=body>stream</a>.

<li><p>Let <var>decoder</var> be a new {{TextDecoderStream}} object in <a>this</a>'s
<a>relevant realm</a>.

<li>
<p><a data-lt="set up a text decoder stream">Set up</a> <var>decoder</var> with <a
for=/>UTF-8</a>.
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@annevk annevk May 21, 2026

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no newline inside phrasing


<p class=note>This is done regardless of the presence or the value of a
`<code>Content-Type</code>` header and regardless of the presence or the value of a
`<code>charset</code>` parameter.</p>

<li><p>Return the result of <var>stream</var>, <a>piped through</a> <var>decoder</var>.
</ol>
</div>


<h3 id=request-class>Request class</h3>

Expand Down