From 511029807a1b88ef811f98056cda8d81c4a06c90 Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Tue, 26 Nov 2024 10:51:45 -0500
Subject: [PATCH] LibJS: Implement Date.prototype.toTemporalInstant

---
 Libraries/LibJS/Runtime/CommonPropertyNames.h |  1 +
 Libraries/LibJS/Runtime/DatePrototype.cpp     | 21 +++++++++++++++++++
 Libraries/LibJS/Runtime/DatePrototype.h       |  2 ++
 .../Date/Date.prototype.toTemporalInstant.js  | 15 +++++++++++++
 4 files changed, 39 insertions(+)
 create mode 100644 Libraries/LibJS/Tests/builtins/Date/Date.prototype.toTemporalInstant.js

diff --git a/Libraries/LibJS/Runtime/CommonPropertyNames.h b/Libraries/LibJS/Runtime/CommonPropertyNames.h
index 9960c83cc85..2a271c5bad0 100644
--- a/Libraries/LibJS/Runtime/CommonPropertyNames.h
+++ b/Libraries/LibJS/Runtime/CommonPropertyNames.h
@@ -538,6 +538,7 @@ namespace JS {
     P(toSpliced)                             \
     P(toString)                              \
     P(total)                                 \
+    P(toTemporalInstant)                     \
     P(toTimeString)                          \
     P(toUpperCase)                           \
     P(toUTCString)                           \
diff --git a/Libraries/LibJS/Runtime/DatePrototype.cpp b/Libraries/LibJS/Runtime/DatePrototype.cpp
index 14740241eb8..fd31423bff3 100644
--- a/Libraries/LibJS/Runtime/DatePrototype.cpp
+++ b/Libraries/LibJS/Runtime/DatePrototype.cpp
@@ -22,6 +22,7 @@
 #include <LibJS/Runtime/Intl/DateTimeFormat.h>
 #include <LibJS/Runtime/Intl/DateTimeFormatConstructor.h>
 #include <LibJS/Runtime/Temporal/AbstractOperations.h>
+#include <LibJS/Runtime/Temporal/Instant.h>
 #include <LibJS/Runtime/Temporal/TimeZone.h>
 #include <LibJS/Runtime/Value.h>
 #include <LibJS/Runtime/ValueInlines.h>
@@ -86,6 +87,8 @@ void DatePrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.toTimeString, to_time_string, 0, attr);
     define_native_function(realm, vm.names.toUTCString, to_utc_string, 0, attr);
 
+    define_native_function(realm, vm.names.toTemporalInstant, to_temporal_instant, 0, attr);
+
     define_native_function(realm, vm.names.getYear, get_year, 0, attr);
     define_native_function(realm, vm.names.setYear, set_year, 1, attr);
 
@@ -1221,6 +1224,24 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::symbol_to_primitive)
     return TRY(this_value.as_object().ordinary_to_primitive(try_first));
 }
 
+// 14.8.1 Date.prototype.toTemporalInstant ( ), https://tc39.es/proposal-temporal/#sec-date.prototype.totemporalinstant
+JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_temporal_instant)
+{
+    // 1. Let dateObject be the this value.
+    // 2. Perform ? RequireInternalSlot(dateObject, [[DateValue]]).
+    auto date_object = TRY(typed_this_value(vm));
+
+    // 3. Let t be dateObject.[[DateValue]].
+    auto time = date_object->date_value();
+
+    // 4. Let ns be ? NumberToBigInt(t) × ℤ(10**6).
+    auto nanoseconds = TRY(number_to_bigint(vm, Value { time }));
+    nanoseconds = BigInt::create(vm, nanoseconds->big_integer().multiplied_by(Temporal::NANOSECONDS_PER_MILLISECOND));
+
+    // 5. Return ! CreateTemporalInstant(ns).
+    return MUST(Temporal::create_temporal_instant(vm, nanoseconds));
+}
+
 // B.2.4.1 Date.prototype.getYear ( ), https://tc39.es/ecma262/#sec-date.prototype.getyear
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_year)
 {
diff --git a/Libraries/LibJS/Runtime/DatePrototype.h b/Libraries/LibJS/Runtime/DatePrototype.h
index c55f5dd4536..bb28e970806 100644
--- a/Libraries/LibJS/Runtime/DatePrototype.h
+++ b/Libraries/LibJS/Runtime/DatePrototype.h
@@ -65,6 +65,8 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(to_time_string);
     JS_DECLARE_NATIVE_FUNCTION(to_utc_string);
 
+    JS_DECLARE_NATIVE_FUNCTION(to_temporal_instant);
+
     JS_DECLARE_NATIVE_FUNCTION(get_year);
     JS_DECLARE_NATIVE_FUNCTION(set_year);
     JS_DECLARE_NATIVE_FUNCTION(to_gmt_string);
diff --git a/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toTemporalInstant.js b/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toTemporalInstant.js
new file mode 100644
index 00000000000..6e3fc6691b6
--- /dev/null
+++ b/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toTemporalInstant.js
@@ -0,0 +1,15 @@
+describe("correct behavior", () => {
+    test("basic functionality", () => {
+        const date = new Date("2021-07-09T01:36:00Z");
+        const instant = date.toTemporalInstant();
+        expect(instant.epochMilliseconds).toBe(1625794560000);
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Date object", () => {
+        expect(() => {
+            Date.prototype.toTemporalInstant.call(123);
+        }).toThrowWithMessage(TypeError, "Not an object of type Date");
+    });
+});