feat(intl): implement Date.prototype.toLocaleString, toLocaleDateString, and toLocaleTimeString 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	50,073	50,079	+6
Ignored	2,072	2,072	0
Failed	818	812	-6
Panics	0	0	0
Conformance	94.54%	94.55%	+0.01%

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: 197b736bb87523a14b41834c078adbec3059d237
Tested PR commit: 60b64009c79053522578466b33de32416a2f0e33
Compare commits: 197b736...60b6400

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

…void JS alloc in Date toLocaleString path

codecov · 2026-03-15T02:36:29Z

Codecov Report

❌ Patch coverage is 95.00000% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.32%. Comparing base (6ddc2b4) to head (60b6400).
⚠️ Report is 891 commits behind head on main.

Files with missing lines	Patch %	Lines
...e/engine/src/builtins/intl/date_time_format/mod.rs	94.82%	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%   59.32%   +12.08%     
===========================================
  Files         476      563       +87     
  Lines       46892    62848    +15956     
===========================================
+ Hits        22154    37285    +15131     
- Misses      24738    25563      +825

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

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!

jedel1043 · 2026-03-16T20:32:09Z

Deferring to @nekevss for the final review, but LGTM from my side

nekevss

I think one last issue and then this should probably be good.

nekevss · 2026-03-16T21:55:07Z

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

+    timestamp: f64,
+    context: &mut Context,
+) -> JsResult<JsString> {
+    let time_zone_offset = match dtf.time_zone {


issue: keep the doc lines that are applied with the methods.

Adapting dtf can be incredibly complicated, and this function is probably going to need to be updated / reworked in order to support temporal. So keeping the comments in this instance is very important.

…steps

alienx5499 · 2026-03-17T06:40:33Z

Hi @nekevss, I’ve pushed commit 6b270bf addressing your comment.

It keeps the spec step documentation alongside format_timestamp_with_dtf and introduces a time_zone binding to better mirror the spec flow and reuse the value.

Would appreciate a re-review when you have time.

alienx5499 · 2026-03-18T18:28:48Z

Hi @nekevss,

Just following up on this, I’ve addressed all the previous review comments and incorporated the requested changes.

Please let me know if there’s anything else I should update or refine. Happy to iterate further.

Thanks!

jedel1043 · 2026-03-18T18:34:10Z

Please don't repeatedly ping maintainers. A single request for review is enough. We'll review when we have the time

nekevss

Generally looks good to me.

We'll have to keep in mind how this may need to expand in order to support Temporal in the future, but that's all TBD

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

core/engine/src/builtins/intl/date_time_format/mod.rs Show resolved Hide resolved

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

Open

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

jedel1043 removed their request for review March 16, 2026 20:32

jedel1043 removed the Waiting On Author Waiting on PR changes from the author label Mar 16, 2026

nekevss requested changes Mar 16, 2026

View reviewed changes

alienx5499 changed the title ~~feat(intl): implement Date.prototype.toLocaleString, toLocaleDateStri…~~ feat(intl): implement Date.prototype.toLocaleString, toLocaleDateString, and toLocaleTimeString Mar 17, 2026

feat(intl): align DateTimeFormat timestamp formatting docs with spec …

6b270bf

…steps

Merge branch 'main' into feat/5075-date-tolocalestring

60b6400

alienx5499 requested a review from nekevss March 17, 2026 10:58

nekevss approved these changes Mar 19, 2026

View reviewed changes

nekevss added this pull request to the merge queue Mar 19, 2026

Merged via the queue into boa-dev:main with commit 26271b7 Mar 19, 2026
22 checks passed

github-actions bot removed the Waiting On Review Waiting on reviews from the maintainers label Mar 19, 2026

Uh oh!

Conversation

alienx5499 commented Mar 15, 2026

Testing

Uh oh!

github-actions bot commented Mar 15, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Test262 conformance changes

Uh oh!

Uh oh!

codecov bot commented Mar 15, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Codecov Report

Uh oh!

nekevss left a comment

Choose a reason for hiding this comment

Uh oh!

nekevss Mar 15, 2026

Choose a reason for hiding this comment

Uh oh!

nekevss Mar 15, 2026

Choose a reason for hiding this comment

Uh oh!

nekevss Mar 15, 2026

Choose a reason for hiding this comment

Uh oh!

nekevss Mar 15, 2026

Choose a reason for hiding this comment

Uh oh!

nekevss Mar 15, 2026

Choose a reason for hiding this comment

Uh oh!

alienx5499 commented Mar 16, 2026

Uh oh!

jedel1043 commented Mar 16, 2026

Uh oh!

nekevss left a comment

Choose a reason for hiding this comment

Uh oh!

nekevss Mar 16, 2026

Choose a reason for hiding this comment

Uh oh!

alienx5499 commented Mar 17, 2026

Uh oh!

alienx5499 commented Mar 18, 2026

Uh oh!

jedel1043 commented Mar 18, 2026

Uh oh!

nekevss left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

github-actions bot commented Mar 15, 2026 •

edited

Loading

codecov bot commented Mar 15, 2026 •

edited

Loading