feat(intl): implement Date.prototype.toLocaleString, toLocaleDateStri… by alienx5499 · Pull Request #5080 · boa-dev/boa

alienx5499 · 2026-03-15T00:28:59Z

This Pull Request fixes/closes #5075.

It changes the following:

Implement Date.prototype.toLocaleString, toLocaleDateString, and toLocaleTimeString using Intl.DateTimeFormat when the intl feature is enabled (ECMA-402 20.4.1–20.4.3).
Add shared helper format_date_time_locale in intl/date_time_format; expose create_date_time_format as pub(crate); add FormatDefaults::All and fix default-application logic for it.
Add this_date_value helper for the RequireInternalSlot / [[DateValue]] step in the three methods.
Return "Invalid Date" for NaN in all three methods; when intl is disabled, fall back to Date.prototype.toString.
Add #[cfg(feature = "intl")] tests: invalid receiver (TypeError), NaN → "Invalid Date", typeof checks, locale differences (en-US vs de-DE) for all three methods, and options pipeline (dateStyle: 'short').

Testing

cargo test -p boa_engine --lib -- date::tests::date_proto_to_locale_string_intl (without intl; test is skipped)
cargo test -p boa_engine --features intl_bundled --lib -- date::tests::date_proto_to_locale_string_intl (with intl)

…ng, and toLocaleTimeString

github-actions · 2026-03-15T00:38:29Z

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,070	49,941	-129
Ignored	2,072	2,207	+135
Failed	821	815	-6
Panics	0	0	0
Conformance	94.54%	94.29%	-0.24%

Fixed tests (6):

test/intl402/Date/prototype/this-value-invalid-date.js (previously Failed)
test/intl402/Date/prototype/this-value-non-date.js (previously Failed)
test/intl402/Date/prototype/taint-Intl-DateTimeFormat.js (previously Failed)
test/intl402/Date/prototype/throws-same-exceptions-as-DateTimeFormat.js (previously Failed)
test/intl402/Date/prototype/toLocaleString/default-options-object-prototype.js (previously Failed)
test/staging/sm/misc/builtin-methods-reject-null-undefined-this.js (previously Failed)

Tested main commit: 965f38c66d22dbcda4746d9b79c607189530287d
Tested PR commit: 755481e9dac8aa567a1642d658a1537444b27515
Compare commits: 965f38c...755481e

jedel1043 · 2026-03-15T01:09:24Z

core/engine/src/builtins/intl/date_time_format/mod.rs

+    let options = coerce_options_to_object(options, context)?;
+    if format_type != FormatType::Time
+        && get_option::<DateStyle>(&options, js_string!("dateStyle"), context)?.is_none()
+    {
+        options.create_data_property_or_throw(
+            js_string!("dateStyle"),
+            JsValue::from(js_string!("long")),
+            context,
+        )?;
+    }
+    if format_type != FormatType::Date
+        && get_option::<TimeStyle>(&options, js_string!("timeStyle"), context)?.is_none()
+    {
+        options.create_data_property_or_throw(
+            js_string!("timeStyle"),
+            JsValue::from(js_string!("long")),
+            context,
+        )?;
+    }
+    let new_target = context
+        .intrinsics()
+        .constructors()
+        .date_time_format()
+        .constructor()
+        .into();
+    let options_value = options.into();
+    let dtf = create_date_time_format(
+        &new_target,
+        locales,
+        &options_value,
+        format_type,
+        defaults,
+        context,
+    )?;
+    let format_val = dtf.get(js_string!("format"), context)?;
+    let format_fn = format_val
+        .as_callable()
+        .ok_or_else(|| JsNativeError::typ().with_message("format is not callable"))?;
+    format_fn.call(&dtf.into(), &[JsValue::from(timestamp)], context)
+}


I don't think this is the correct approach. This is interacting with DateTimeFormat as if it was an external crate to be consumed, but since the creation of the formatter is not visible to the external world, we can get away with calling create_date_time_format directly.

My suggestion here would be to tweak create_date_time_format such that it returns DateTimeFormatter directly, then use that here to avoid creating a new JsObject, and move the object creation logic to the constructor instead

Kinda weird to do it this way in here but use the correct approach in Number.prototype.toLocaleString by the way

Thanks for the suggestion! I refactored create_date_time_format to return the internal DateTimeFormat and moved the JsObject creation into the constructor. Date.prototype.toLocaleString and related methods now format directly using the internal formatter, similar to Number.prototype.toLocaleString. Addressed in 725441e.

…void JS alloc in Date toLocaleString path

codecov · 2026-03-15T02:36:29Z

Codecov Report

❌ Patch coverage is 94.89796% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.02%. Comparing base (6ddc2b4) to head (755481e).
⚠️ Report is 857 commits behind head on main.

Files with missing lines	Patch %	Lines
...e/engine/src/builtins/intl/date_time_format/mod.rs	94.64%	3 Missing ⚠️
core/engine/src/builtins/date/mod.rs	95.23%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5080       +/-   ##
===========================================
+ Coverage   47.24%   59.02%   +11.78%     
===========================================
  Files         476      563       +87     
  Lines       46892    62725    +15833     
===========================================
+ Hits        22154    37026    +14872     
- Misses      24738    25699      +961

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nekevss

Noticed a couple things while reviewing this.

nekevss · 2026-03-15T20:27:00Z

core/engine/src/builtins/date/mod.rs

        func.call(this, &[], context)
    }

+    /// Returns the `[[DateValue]]` internal slot (RequireInternalSlot(dateObject, `[[DateValue]]`)).


nit: accessing the inner field should remain as the current style.

nekevss · 2026-03-15T20:35:50Z

core/engine/src/builtins/date/mod.rs

+        // Let dateObject be the this value.
+        // Perform ? RequireInternalSlot(dateObject, [[DateValue]]).
+        // Let x be dateObject.[[DateValue]].
+        let t = Self::this_date_value(this)?;


issue: these steps are only applicable to the intl flagged implementation.

nekevss · 2026-03-15T20:36:22Z

core/engine/src/builtins/date/mod.rs

-        Err(JsError::from_opaque(JsValue::new(js_string!(
-            "Function Unimplemented]"
-        ))))
+        // Let dateObject be the this value.


nit: style, include the step numbers alongside the spec steps

nekevss · 2026-03-15T20:40:41Z

core/engine/src/builtins/intl/date_time_format/mod.rs

        let needs_defaults = format_options.check_dtf_type(date_time_format_type);
        // d. If needDefaults is true and defaults is either date or all, then
-        if needs_defaults && defaults != FormatDefaults::Time {
+        if needs_defaults && (defaults == FormatDefaults::All || defaults == FormatDefaults::Date) {


question: why was this changed? The previous looks correct and acts in less steps

nekevss · 2026-03-15T20:47:00Z

core/engine/src/builtins/intl/date_time_format/mod.rs

+    context: &mut Context,
+) -> JsResult<JsString> {
+    // FormatDateTime / PartitionDateTimePattern: TimeClip, then ToLocalTime, then format.
+    let x = time_clip(timestamp);


issue: we should not be handling this logic again.

We already handle this logic in two different places. There should not be a reason to implement it a second time. Maybe you're looking for ToLocalTime?

…entation

alienx5499 · 2026-03-16T18:53:41Z

Hi @nekevss,

I've pushed updates addressing the review comments and resolved the outdated threads. Could you please take another look when you have time?

Thanks!

feat(intl): implement Date.prototype.toLocaleString, toLocaleDateStri…

00c5cb5

…ng, and toLocaleTimeString

alienx5499 requested review from a team, jedel1043 and nekevss as code owners March 15, 2026 00:29

github-actions bot added C-Tests Issues and PRs related to the tests. C-Builtins PRs and Issues related to builtins/intrinsics C-Intl Changes related to the `Intl` implementation Waiting On Review Waiting on reviews from the maintainers labels Mar 15, 2026

github-actions bot added this to the v1.0.0 milestone Mar 15, 2026

jedel1043 reviewed Mar 15, 2026

View reviewed changes

jedel1043 added Waiting On Author Waiting on PR changes from the author and removed Waiting On Review Waiting on reviews from the maintainers labels Mar 15, 2026

refactor(intl): return DateTimeFormat from create_date_time_format, a…

725441e

…void JS alloc in Date toLocaleString path

github-actions bot added the Waiting On Review Waiting on reviews from the maintainers label Mar 15, 2026

JkrishnaD mentioned this pull request Mar 15, 2026

feat(intl): implement Temporal.Instant.prototype.toLocaleString #5096

Open

This was referenced Mar 15, 2026

feat(intl): implement Temporal.PlainYearMonth.prototype.toLocaleString #5098

Draft

Implement Temporal.PlainYearMonth.prototype.toLocaleString #5083

Open

alienx5499 requested a review from jedel1043 March 15, 2026 11:14

This was referenced Mar 15, 2026

Implement Temporal.PlainTime.prototype.toLocaleString #5084

Open

Implement Temporal.PlainMonthDay.prototype.toLocaleString #5085

Open

Implement Temporal.PlainDateTime.prototype.toLocaleString #5086

Open

nekevss requested changes Mar 15, 2026

View reviewed changes

refactor(intl): improve Date toLocaleString and DateTimeFormat implem…

755481e

…entation

alienx5499 force-pushed the feat/5075-date-tolocalestring branch from fa1bd92 to 755481e Compare March 15, 2026 21:49

alienx5499 requested a review from nekevss March 15, 2026 21:52

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