LibJS: Re-implement the Date constructor / prototype for spec compliance

First, this adds a constructor to the Date object to be created from a
plain double. This is a first step to removing Core::DateTime as the
basis for the Date object. A subsequent commit will remove the now-
unused data from the object.

Next, this implements the constructor in accordance to the spec. The
constructor when NewTarget is undefined no longer allocates a Date on
the heap. The other constructor properly uses recently created AOs to
handle time zone and ensure the created [[DateValue]] is valid. Other
methods on the constructor (Date.now) have not been touched yet.

Last, the prototype is reimplemented. Again, we use other AOs to handle
time zones and time clipping. Not all prototypes are fixed; most of them
are, but a few (e.g. Date.prototype.getTimezoneOffset) were not fixed,
but left in a mostly unimplemented state for another commit.

In all of the above, spec comments are added. This is a rather large
change; but it's tough to do any of these parts individually without
breaking everything else.

9 files changed, 499 insertions, 483 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/Date.cpp b/Userland/Libraries/LibJS/Runtime/Date.cpp
index 14683138a9..b3d59f1c3e 100644
--- a/Userland/Libraries/LibJS/Runtime/Date.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Date.cpp
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020-2021, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022, Tim Flynn <trflynn89@pm.me>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -20,6 +21,11 @@ Date* Date::create(GlobalObject& global_object, Core::DateTime datetime, i16 mil
     return global_object.heap().allocate<Date>(global_object, datetime, milliseconds, is_invalid, *global_object.date_prototype());
 }
 
+Date* Date::create(GlobalObject& global_object, double date_value)
+{
+    return global_object.heap().allocate<Date>(global_object, date_value, *global_object.date_prototype());
+}
+
 Date::Date(Core::DateTime datetime, i16 milliseconds, bool is_invalid, Object& prototype)
     : Object(prototype)
     , m_datetime(datetime)
@@ -28,6 +34,12 @@ Date::Date(Core::DateTime datetime, i16 milliseconds, bool is_invalid, Object& p
 {
 }
 
+Date::Date(double date_value, Object& prototype)
+    : Object(prototype)
+    , m_date_value(date_value)
+{
+}
+
 Date::~Date()
 {
 }
@@ -84,9 +96,7 @@ String Date::gmt_date_string() const
 
 String Date::iso_date_string() const
 {
-    auto tm = to_utc_tm();
-    int year = tm.tm_year + 1900;
-    int month = tm.tm_mon + 1;
+    int year = year_from_time(m_date_value);
 
     StringBuilder builder;
     if (year < 0)
@@ -96,17 +106,17 @@ String Date::iso_date_string() const
     else
         builder.appendff("{:04}", year);
     builder.append('-');
-    builder.appendff("{:02}", month);
+    builder.appendff("{:02}", month_from_time(m_date_value) + 1);
     builder.append('-');
-    builder.appendff("{:02}", tm.tm_mday);
+    builder.appendff("{:02}", date_from_time(m_date_value));
     builder.append('T');
-    builder.appendff("{:02}", tm.tm_hour);
+    builder.appendff("{:02}", hour_from_time(m_date_value));
     builder.append(':');
-    builder.appendff("{:02}", tm.tm_min);
+    builder.appendff("{:02}", min_from_time(m_date_value));
     builder.append(':');
-    builder.appendff("{:02}", tm.tm_sec);
+    builder.appendff("{:02}", sec_from_time(m_date_value));
     builder.append('.');
-    builder.appendff("{:03}", m_milliseconds);
+    builder.appendff("{:03}", ms_from_time(m_date_value));
     builder.append('Z');
 
     return builder.build();
diff --git a/Userland/Libraries/LibJS/Runtime/Date.h b/Userland/Libraries/LibJS/Runtime/Date.h
index 1829bcbc48..7072ae4e06 100644
--- a/Userland/Libraries/LibJS/Runtime/Date.h
+++ b/Userland/Libraries/LibJS/Runtime/Date.h
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020-2021, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022, Tim Flynn <trflynn89@pm.me>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -19,11 +20,16 @@ public:
     static constexpr double time_clip = 8.64e15;
 
     static Date* create(GlobalObject&, Core::DateTime, i16 milliseconds, bool is_invalid);
+    static Date* create(GlobalObject&, double date_value);
     static Date* now(GlobalObject&);
 
     Date(Core::DateTime datetime, i16 milliseconds, bool is_invalid, Object& prototype);
+    Date(double date_value, Object& prototype);
     virtual ~Date() override;
 
+    double date_value() const { return m_date_value; }
+    void set_date_value(double value) { m_date_value = value; }
+
     Core::DateTime& datetime() { return m_datetime; }
     const Core::DateTime& datetime() const { return m_datetime; }
 
@@ -74,20 +80,14 @@ public:
     String locale_string() const { return m_datetime.to_string(); }
     String locale_time_string() const { return m_datetime.to_string("%H:%M:%S"); }
 
-    // https://tc39.es/ecma262/#sec-properties-of-date-instances
-    // [[DateValue]]
-    double date_value() const
-    {
-        return m_is_invalid
-            ? AK::NaN<double>
-            : static_cast<double>(m_datetime.timestamp() * 1000 + m_milliseconds);
-    }
-
 private:
     tm to_utc_tm() const;
 
+    double m_date_value { 0 }; // [[DateValue]]
+
     Core::DateTime m_datetime;
     i16 m_milliseconds;
+
     bool m_is_invalid { false };
 };
 
diff --git a/Userland/Libraries/LibJS/Runtime/DateConstructor.cpp b/Userland/Libraries/LibJS/Runtime/DateConstructor.cpp
index a49d74f9b5..7884376ba9 100644
--- a/Userland/Libraries/LibJS/Runtime/DateConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/DateConstructor.cpp
@@ -2,6 +2,7 @@
  * Copyright (c) 2020, Linus Groh <linusg@serenityos.org>
  * Copyright (c) 2020, Nico Weber <thakis@chromium.org>
  * Copyright (c) 2021, Petróczi Zoltán <petroczizoltan@tutanota.com>
+ * Copyright (c) 2022, Tim Flynn <trflynn89@pm.me>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -13,6 +14,7 @@
 #include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/Date.h>
 #include <LibJS/Runtime/DateConstructor.h>
+#include <LibJS/Runtime/DatePrototype.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/VM.h>
 #include <sys/time.h>
@@ -156,26 +158,15 @@ DateConstructor::~DateConstructor()
 {
 }
 
-struct DatetimeAndMilliseconds {
-    Core::DateTime datetime;
-    i16 milliseconds { 0 };
-};
-
-static DatetimeAndMilliseconds now()
-{
-    struct timeval tv;
-    gettimeofday(&tv, nullptr);
-    auto datetime = Core::DateTime::now();
-    auto milliseconds = static_cast<i16>(tv.tv_usec / 1000);
-    return { datetime, milliseconds };
-}
-
 // 21.4.2.1 Date ( ...values ), https://tc39.es/ecma262/#sec-date
 ThrowCompletionOr<Value> DateConstructor::call()
 {
-    auto [datetime, milliseconds] = JS::now();
-    auto* date = Date::create(global_object(), datetime, milliseconds, false);
-    return js_string(heap(), date->string());
+    // 1. If NewTarget is undefined, then
+    //     a. Let now be the time value (UTC) identifying the current time.
+    auto now = AK::Time::now_realtime().to_milliseconds();
+
+    //     b. Return ToDateString(now).
+    return js_string(vm(), to_date_string(now));
 }
 
 // 21.4.2.1 Date ( ...values ), https://tc39.es/ecma262/#sec-date
@@ -184,91 +175,94 @@ ThrowCompletionOr<Object*> DateConstructor::construct(FunctionObject& new_target
     auto& vm = this->vm();
     auto& global_object = this->global_object();
 
+    Value date_value;
+
+    // 2. Let numberOfArgs be the number of elements in values.
+    // 3. If numberOfArgs = 0, then
     if (vm.argument_count() == 0) {
-        auto [datetime, milliseconds] = JS::now();
-        return TRY(ordinary_create_from_constructor<Date>(global_object, new_target, &GlobalObject::date_prototype, datetime, milliseconds, false));
+        // a. Let dv be the time value (UTC) identifying the current time.
+        auto now = AK::Time::now_realtime().to_milliseconds();
+        date_value = Value(static_cast<double>(now));
     }
+    // 4. Else if numberOfArgs = 1, then
+    else if (vm.argument_count() == 1) {
+        // a. Let value be values[0].
+        auto value = vm.argument(0);
+        Value time_value;
 
-    auto create_invalid_date = [&global_object, &new_target]() -> ThrowCompletionOr<Date*> {
-        auto datetime = Core::DateTime::create(1970, 1, 1, 0, 0, 0);
-        auto milliseconds = static_cast<i16>(0);
-        return ordinary_create_from_constructor<Date>(global_object, new_target, &GlobalObject::date_prototype, datetime, milliseconds, true);
-    };
+        // b. If Type(value) is Object and value has a [[DateValue]] internal slot, then
+        if (value.is_object() && is<Date>(value.as_object())) {
+            // i. Let tv be ! thisTimeValue(value).
+            time_value = MUST(this_time_value(global_object, value));
+        }
+        // c. Else,
+        else {
+            // i. Let v be ? ToPrimitive(value).
+            auto primitive = TRY(value.to_primitive(global_object));
+
+            // ii. If Type(v) is String, then
+            if (primitive.is_string()) {
+                // 1. Assert: The next step never returns an abrupt completion because Type(v) is String.
+                // 2. Let tv be the result of parsing v as a date, in exactly the same manner as for the parse method (21.4.3.2).
+                time_value = parse_date_string(global_object, primitive.as_string().string());
+            }
+            // iii. Else,
+            else {
+                // 1. Let tv be ? ToNumber(v).
+                time_value = TRY(primitive.to_number(global_object));
+            }
+        }
 
-    if (vm.argument_count() == 1) {
-        auto value = vm.argument(0);
-        if (value.is_string())
-            value = parse_date_string(global_object, value.as_string().string());
-        else
-            value = TRY(value.to_number(global_object));
-
-        if (!value.is_finite_number())
-            return TRY(create_invalid_date());
-
-        // A timestamp since the epoch, in UTC.
-        double value_as_double = value.as_double();
-        if (value_as_double > Date::time_clip)
-            return TRY(create_invalid_date());
-        auto datetime = Core::DateTime::from_timestamp(static_cast<time_t>(value_as_double / 1000));
-        auto milliseconds = static_cast<i16>(fmod(value_as_double, 1000));
-        return TRY(ordinary_create_from_constructor<Date>(global_object, new_target, &GlobalObject::date_prototype, datetime, milliseconds, false));
+        // d. Let dv be TimeClip(tv).
+        date_value = time_clip(global_object, time_value);
     }
+    // 5. Else,
+    else {
+        // a. Assert: numberOfArgs ≥ 2.
+        // b. Let y be ? ToNumber(values[0]).
+        auto year = TRY(vm.argument(0).to_number(global_object));
+        // c. Let m be ? ToNumber(values[1]).
+        auto month = TRY(vm.argument(1).to_number(global_object));
+
+        auto arg_or = [&vm, &global_object](size_t i, i32 fallback) -> ThrowCompletionOr<Value> {
+            return vm.argument_count() > i ? vm.argument(i).to_number(global_object) : Value(fallback);
+        };
+
+        // d. If numberOfArgs > 2, let dt be ? ToNumber(values[2]); else let dt be 1𝔽.
+        auto date = TRY(arg_or(2, 1));
+        // e. If numberOfArgs > 3, let h be ? ToNumber(values[3]); else let h be +0𝔽.
+        auto hours = TRY(arg_or(3, 0));
+        // f. If numberOfArgs > 4, let min be ? ToNumber(values[4]); else let min be +0𝔽.
+        auto minutes = TRY(arg_or(4, 0));
+        // g. If numberOfArgs > 5, let s be ? ToNumber(values[5]); else let s be +0𝔽.
+        auto seconds = TRY(arg_or(5, 0));
+        // h. If numberOfArgs > 6, let milli be ? ToNumber(values[6]); else let milli be +0𝔽.
+        auto milliseconds = TRY(arg_or(6, 0));
+
+        // i. If y is NaN, let yr be NaN.
+        // j. Else,
+        if (!year.is_nan()) {
+            // i. Let yi be ! ToIntegerOrInfinity(y).
+            auto year_double = MUST(year.to_integer_or_infinity(global_object));
+
+            // ii. If 0 ≤ yi ≤ 99, let yr be 1900𝔽 + 𝔽(yi); otherwise, let yr be y.
+            if (0 <= year_double && year_double <= 99)
+                year = Value(1900 + year_double);
+        }
 
-    // A date/time in components, in local time.
-    auto arg_or = [&vm, &global_object](size_t i, i32 fallback) -> ThrowCompletionOr<Value> {
-        return vm.argument_count() > i ? vm.argument(i).to_number(global_object) : Value(fallback);
-    };
+        // k. Let finalDate be MakeDate(MakeDay(yr, m, dt), MakeTime(h, min, s, milli)).
+        auto day = make_day(global_object, year, month, date);
+        auto time = make_time(global_object, hours, minutes, seconds, milliseconds);
+        auto final_date = make_date(day, time);
 
-    auto year_value = TRY(vm.argument(0).to_number(global_object));
-    if (!year_value.is_finite_number())
-        return TRY(create_invalid_date());
-    auto year = year_value.as_i32();
-
-    auto month_index_value = TRY(vm.argument(1).to_number(global_object));
-    if (!month_index_value.is_finite_number())
-        return TRY(create_invalid_date());
-    auto month_index = month_index_value.as_i32();
-
-    auto day_value = TRY(arg_or(2, 1));
-    if (!day_value.is_finite_number())
-        return TRY(create_invalid_date());
-    auto day = day_value.as_i32();
-
-    auto hours_value = TRY(arg_or(3, 0));
-    if (!hours_value.is_finite_number())
-        return TRY(create_invalid_date());
-    auto hours = hours_value.as_i32();
-
-    auto minutes_value = TRY(arg_or(4, 0));
-    if (!minutes_value.is_finite_number())
-        return TRY(create_invalid_date());
-    auto minutes = minutes_value.as_i32();
-
-    auto seconds_value = TRY(arg_or(5, 0));
-    if (!seconds_value.is_finite_number())
-        return TRY(create_invalid_date());
-    auto seconds = seconds_value.as_i32();
-
-    auto milliseconds_value = TRY(arg_or(6, 0));
-    if (!milliseconds_value.is_finite_number())
-        return TRY(create_invalid_date());
-    auto milliseconds = milliseconds_value.as_i32();
-
-    seconds += milliseconds / 1000;
-    milliseconds %= 1000;
-    if (milliseconds < 0) {
-        seconds -= 1;
-        milliseconds += 1000;
+        // l. Let dv be TimeClip(UTC(finalDate)).
+        date_value = time_clip(global_object, Value(utc_time(final_date.as_double())));
     }
 
-    if (year >= 0 && year <= 99)
-        year += 1900;
-    int month = month_index + 1;
-    auto datetime = Core::DateTime::create(year, month, day, hours, minutes, seconds);
-    auto time = datetime.timestamp() * 1000.0 + milliseconds;
-    if (time > Date::time_clip)
-        return TRY(create_invalid_date());
-    return TRY(ordinary_create_from_constructor<Date>(global_object, new_target, &GlobalObject::date_prototype, datetime, milliseconds, false));
+    // 6. Let O be ? OrdinaryCreateFromConstructor(NewTarget, "%Date.prototype%", « [[DateValue]] »).
+    // 7. Set O.[[DateValue]] to dv.
+    // 8. Return O.
+    return TRY(ordinary_create_from_constructor<Date>(global_object, new_target, &GlobalObject::date_prototype, date_value.as_double()));
 }
 
 // 21.4.3.1 Date.now ( ), https://tc39.es/ecma262/#sec-date.now
diff --git a/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp b/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
index 5af3da296e..713d2f4243 100644
--- a/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
@@ -2,6 +2,7 @@
  * Copyright (c) 2020-2021, Linus Groh <linusg@serenityos.org>
  * Copyright (c) 2021, Petróczi Zoltán <petroczizoltan@tutanota.com>
  * Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
+ * Copyright (c) 2022, Tim Flynn <trflynn89@pm.me>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -125,100 +126,120 @@ ThrowCompletionOr<Value> this_time_value(GlobalObject& global_object, Value valu
 // 21.4.4.2 Date.prototype.getDate ( ), https://tc39.es/ecma262/#sec-date.prototype.getdate
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_date)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->date());
+    // 3. Return DateFromTime(LocalTime(t)).
+    return Value(date_from_time(local_time(time.as_double())));
 }
 
 // 21.4.4.3 Date.prototype.getDay ( ), https://tc39.es/ecma262/#sec-date.prototype.getday
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_day)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->day());
+    // 3. Return WeekDay(LocalTime(t)).
+    return Value(week_day(local_time(time.as_double())));
 }
 
 // 21.4.4.4 Date.prototype.getFullYear ( ), https://tc39.es/ecma262/#sec-date.prototype.getfullyear
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_full_year)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->year());
+    // 3. Return YearFromTime(LocalTime(t)).
+    return Value(year_from_time(local_time(time.as_double())));
 }
 
 // 21.4.4.5 Date.prototype.getHours ( ), https://tc39.es/ecma262/#sec-date.prototype.gethours
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_hours)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->hours());
+    // 3. Return HourFromTime(LocalTime(t)).
+    return Value(hour_from_time(local_time(time.as_double())));
 }
 
 // 21.4.4.6 Date.prototype.getMilliseconds ( ), https://tc39.es/ecma262/#sec-date.prototype.getmilliseconds
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_milliseconds)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->milliseconds());
+    // 3. Return msFromTime(LocalTime(t)).
+    return Value(ms_from_time(local_time(time.as_double())));
 }
 
 // 21.4.4.7 Date.prototype.getMinutes ( ), https://tc39.es/ecma262/#sec-date.prototype.getminutes
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_minutes)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->minutes());
+    // 3. Return MinFromTime(LocalTime(t)).
+    return Value(min_from_time(local_time(time.as_double())));
 }
 
 // 21.4.4.8 Date.prototype.getMonth ( ), https://tc39.es/ecma262/#sec-date.prototype.getmonth
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_month)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->month());
+    // 3. Return MonthFromTime(LocalTime(t)).
+    return Value(month_from_time(local_time(time.as_double())));
 }
 
 // 21.4.4.9 Date.prototype.getSeconds ( ), https://tc39.es/ecma262/#sec-date.prototype.getseconds
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_seconds)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->seconds());
+    // 3. Return SecFromTime(LocalTime(t)).
+    return Value(sec_from_time(local_time(time.as_double())));
 }
 
 // 21.4.4.10 Date.prototype.getTime ( ), https://tc39.es/ecma262/#sec-date.prototype.gettime
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_time)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
-
-    if (this_object->is_invalid())
-        return js_nan();
-
-    return Value(this_object->time());
+    // 1. Return ? thisTimeValue(this value).
+    return this_time_value(global_object, vm.this_value(global_object));
 }
 
 // 21.4.4.11 Date.prototype.getTimezoneOffset ( ), https://tc39.es/ecma262/#sec-date.prototype.gettimezoneoffset
@@ -226,7 +247,7 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_timezone_offset)
 {
     auto* this_object = TRY(typed_this_object(global_object));
 
-    if (this_object->is_invalid())
+    if (!Value(this_object->date_value()).is_finite_number())
         return js_nan();
 
     // FIXME: Make this actually do something once we support timezones instead of just UTC
@@ -236,395 +257,380 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_timezone_offset)
 // 21.4.4.12 Date.prototype.getUTCDate ( ), https://tc39.es/ecma262/#sec-date.prototype.getutcdate
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_date)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->utc_date());
+    // 3. Return DateFromTime(t).
+    return Value(date_from_time(time.as_double()));
 }
 
 // 21.4.4.13 Date.prototype.getUTCDay ( ), https://tc39.es/ecma262/#sec-date.prototype.getutcday
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_day)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->utc_day());
+    // 3. Return WeekDay(t).
+    return Value(week_day(time.as_double()));
 }
 
 // 21.4.4.14 Date.prototype.getUTCFullYear ( ), https://tc39.es/ecma262/#sec-date.prototype.getutcfullyear
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_full_year)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->utc_full_year());
+    // 3. Return YearFromTime(t).
+    return Value(year_from_time(time.as_double()));
 }
 
 // 21.4.4.15 Date.prototype.getUTCHours ( ), https://tc39.es/ecma262/#sec-date.prototype.getutchours
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_hours)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->utc_hours());
+    // 3. Return HourFromTime(t).
+    return Value(hour_from_time(time.as_double()));
 }
 
 // 21.4.4.16 Date.prototype.getUTCMilliseconds ( ), https://tc39.es/ecma262/#sec-date.prototype.getutcmilliseconds
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_milliseconds)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->utc_milliseconds());
+    // 3. Return msFromTime(t).
+    return Value(ms_from_time(time.as_double()));
 }
 
 // 21.4.4.17 Date.prototype.getUTCMinutes ( ), https://tc39.es/ecma262/#sec-date.prototype.getutcminutes
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_minutes)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->utc_minutes());
+    // 3. Return MinFromTime(t).
+    return Value(min_from_time(time.as_double()));
 }
 
 // 21.4.4.18 Date.prototype.getUTCMonth ( ), https://tc39.es/ecma262/#sec-date.prototype.getutcmonth
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_month)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->utc_month());
+    // 3. Return MonthFromTime(t).
+    return Value(month_from_time(time.as_double()));
 }
 
 // 21.4.4.19 Date.prototype.getUTCSeconds ( ), https://tc39.es/ecma262/#sec-date.prototype.getutcseconds
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_seconds)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
+
+    // 3. Return SecFromTime(t).
+    return Value(sec_from_time(time.as_double()));
+}
+
+template<typename T>
+static ThrowCompletionOr<Value> argument_or_value(GlobalObject& global_object, size_t index, T fallback)
+{
+    auto& vm = global_object.vm();
+
+    if (vm.argument_count() > index)
+        return vm.argument(index).to_number(global_object);
 
-    return Value(this_object->utc_seconds());
+    return Value(fallback);
 }
 
 // 21.4.4.20 Date.prototype.setDate ( date ), https://tc39.es/ecma262/#sec-date.prototype.setdate
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_date)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be LocalTime(? thisTimeValue(this value)).
+    auto this_time = TRY(this_time_value(global_object, vm.this_value(global_object)));
+    auto time = local_time(this_time.as_double());
 
-    auto& datetime = this_object->datetime();
+    // 2. Let dt be ? ToNumber(date).
+    auto date = TRY(vm.argument(0).to_number(global_object));
 
-    auto new_date_value = TRY(vm.argument(0).to_number(global_object));
-    if (!new_date_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_date = new_date_value.as_i32();
+    // 3. Let newDate be MakeDate(MakeDay(YearFromTime(t), MonthFromTime(t), dt), TimeWithinDay(t)).
+    auto year = Value(year_from_time(time));
+    auto month = Value(month_from_time(time));
 
-    datetime.set_time(datetime.year(), datetime.month(), new_date, datetime.hour(), datetime.minute(), datetime.second());
-    if (this_object->time() > Date::time_clip) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
+    auto day = make_day(global_object, year, month, date);
+    auto new_date = make_date(day, Value(time_within_day(time)));
+
+    // 4. Let u be TimeClip(UTC(newDate)).
+    new_date = time_clip(global_object, Value(utc_time(new_date.as_double())));
 
-    this_object->set_is_invalid(false);
-    return Value(this_object->time());
+    // 5. Set the [[DateValue]] internal slot of this Date object to u.
+    auto* this_object = MUST(typed_this_object(global_object));
+    this_object->set_date_value(new_date.as_double());
+
+    // 6. Return u.
+    return new_date;
 }
 
 // 21.4.4.21 Date.prototype.setFullYear ( year [ , month [ , date ] ] ), https://tc39.es/ecma262/#sec-date.prototype.setfullyear
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_full_year)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto this_time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    auto& datetime = this_object->datetime();
+    // 2. If t is NaN, set t to +0𝔽; otherwise, set t to LocalTime(t).
+    double time = 0;
+    if (!this_time.is_nan())
+        time = local_time(this_time.as_double());
 
-    auto arg_or = [&vm, &global_object](size_t i, i32 fallback) -> ThrowCompletionOr<Value> {
-        return vm.argument_count() > i ? vm.argument(i).to_number(global_object) : Value(fallback);
-    };
+    // 3. Let y be ? ToNumber(year).
+    auto year = TRY(vm.argument(0).to_number(global_object));
 
-    auto new_year_value = TRY(vm.argument(0).to_number(global_object));
-    if (!new_year_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_year = new_year_value.as_i32();
+    // 4. If month is not present, let m be MonthFromTime(t); otherwise, let m be ? ToNumber(month).
+    auto month = TRY(argument_or_value(global_object, 1, month_from_time(time)));
 
-    auto new_month_value = TRY(arg_or(1, datetime.month() - 1));
-    if (!new_month_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_month = new_month_value.as_i32() + 1; // JS Months: 0 - 11, DateTime months: 1-12
+    // 5. If date is not present, let dt be DateFromTime(t); otherwise, let dt be ? ToNumber(date).
+    auto date = TRY(argument_or_value(global_object, 2, date_from_time(time)));
 
-    auto new_day_value = TRY(arg_or(2, datetime.day()));
-    if (!new_day_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_day = new_day_value.as_i32();
+    // 6. Let newDate be MakeDate(MakeDay(y, m, dt), TimeWithinDay(t)).
+    auto day = make_day(global_object, year, month, date);
+    auto new_date = make_date(day, Value(time_within_day(time)));
 
-    datetime.set_time(new_year, new_month, new_day, datetime.hour(), datetime.minute(), datetime.second());
-    if (this_object->time() > Date::time_clip) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
+    // 7. Let u be TimeClip(UTC(newDate)).
+    new_date = time_clip(global_object, Value(utc_time(new_date.as_double())));
 
-    this_object->set_is_invalid(false);
+    // 8. Set the [[DateValue]] internal slot of this Date object to u.
+    auto* this_object = MUST(typed_this_object(global_object));
+    this_object->set_date_value(new_date.as_double());
 
-    return Value(this_object->time());
+    // 9. Return u.
+    return new_date;
 }
 
 // 21.4.4.22 Date.prototype.setHours ( hour [ , min [ , sec [ , ms ] ] ] ), https://tc39.es/ecma262/#sec-date.prototype.sethours
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_hours)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be LocalTime(? thisTimeValue(this value)).
+    auto this_time = TRY(this_time_value(global_object, vm.this_value(global_object)));
+    auto time = local_time(this_time.as_double());
 
-    auto arg_or = [&vm, &global_object](size_t i, i32 fallback) -> ThrowCompletionOr<Value> {
-        return vm.argument_count() > i ? vm.argument(i).to_number(global_object) : Value(fallback);
-    };
+    // 2. Let h be ? ToNumber(hour).
+    auto hour = TRY(vm.argument(0).to_number(global_object));
 
-    auto& datetime = this_object->datetime();
+    // 3. If min is not present, let m be MinFromTime(t); otherwise, let m be ? ToNumber(min).
+    auto minute = TRY(argument_or_value(global_object, 1, min_from_time(time)));
 
-    auto new_hours_value = TRY(vm.argument(0).to_number(global_object));
-    if (!new_hours_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_hours = new_hours_value.as_i32();
+    // 4. If sec is not present, let s be SecFromTime(t); otherwise, let s be ? ToNumber(sec).
+    auto second = TRY(argument_or_value(global_object, 2, sec_from_time(time)));
 
-    auto new_minutes_value = TRY(arg_or(1, datetime.minute()));
-    if (!new_minutes_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_minutes = new_minutes_value.as_i32();
+    // 5. If ms is not present, let milli be msFromTime(t); otherwise, let milli be ? ToNumber(ms).
+    auto millisecond = TRY(argument_or_value(global_object, 3, ms_from_time(time)));
 
-    auto new_seconds_value = TRY(arg_or(2, datetime.second()));
-    if (!new_seconds_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_seconds = new_seconds_value.as_i32();
-
-    auto new_milliseconds_value = TRY(arg_or(3, this_object->milliseconds()));
-    if (!new_milliseconds_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_milliseconds = new_milliseconds_value.as_i32();
+    // 6. Let date be MakeDate(Day(t), MakeTime(h, m, s, milli)).
+    auto new_time = make_time(global_object, hour, minute, second, millisecond);
+    auto date = make_date(Value(day(time)), new_time);
 
-    new_seconds += new_milliseconds / 1000;
-    this_object->set_milliseconds(new_milliseconds % 1000);
+    // 7. Let u be TimeClip(UTC(date)).
+    date = time_clip(global_object, Value(utc_time(date.as_double())));
 
-    datetime.set_time(datetime.year(), datetime.month(), datetime.day(), new_hours, new_minutes, new_seconds);
-    if (this_object->time() > Date::time_clip) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
+    // 8. Set the [[DateValue]] internal slot of this Date object to u.
+    auto* this_object = MUST(typed_this_object(global_object));
+    this_object->set_date_value(date.as_double());
 
-    this_object->set_is_invalid(false);
-    return Value(this_object->time());
+    // 9. Return u.
+    return date;
 }
 
 // 21.4.4.23 Date.prototype.setMilliseconds ( ms ), https://tc39.es/ecma262/#sec-date.prototype.setmilliseconds
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_milliseconds)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
-
-    auto new_milliseconds_value = TRY(vm.argument(0).to_number(global_object));
-
-    if (!new_milliseconds_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
+    // 1. Let t be LocalTime(? thisTimeValue(this value)).
+    auto this_time = TRY(this_time_value(global_object, vm.this_value(global_object)));
+    auto time = local_time(this_time.as_double());
 
-    auto new_milliseconds = new_milliseconds_value.as_i32();
+    // 2. Set ms to ? ToNumber(ms).
+    auto millisecond = TRY(vm.argument(0).to_number(global_object));
 
-    this_object->set_milliseconds(new_milliseconds % 1000);
+    // 3. Let time be MakeTime(HourFromTime(t), MinFromTime(t), SecFromTime(t), ms).
+    auto hour = Value(hour_from_time(time));
+    auto minute = Value(min_from_time(time));
+    auto second = Value(sec_from_time(time));
 
-    auto added_seconds = new_milliseconds / 1000;
-    if (added_seconds > 0) {
-        auto& datetime = this_object->datetime();
-        datetime.set_time(datetime.year(), datetime.month(), datetime.day(), datetime.hour(), datetime.minute(), datetime.second() + added_seconds);
-    }
+    auto new_time = make_time(global_object, hour, minute, second, millisecond);
 
-    if (this_object->time() > Date::time_clip) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
+    // 4. Let u be TimeClip(UTC(MakeDate(Day(t), time))).
+    auto date = make_date(Value(day(time)), new_time);
+    date = time_clip(global_object, Value(utc_time(date.as_double())));
 
-    this_object->set_is_invalid(false);
+    // 5. Set the [[DateValue]] internal slot of this Date object to u.
+    auto* this_object = MUST(typed_this_object(global_object));
+    this_object->set_date_value(date.as_double());
 
-    return Value(this_object->time());
+    // 6. Return u.
+    return date;
 }
 
 // 21.4.4.24 Date.prototype.setMinutes ( min [ , sec [ , ms ] ] ), https://tc39.es/ecma262/#sec-date.prototype.setminutes
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_minutes)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be LocalTime(? thisTimeValue(this value)).
+    auto this_time = TRY(this_time_value(global_object, vm.this_value(global_object)));
+    auto time = local_time(this_time.as_double());
 
-    auto arg_or = [&vm, &global_object](size_t i, i32 fallback) -> ThrowCompletionOr<Value> {
-        return vm.argument_count() > i ? vm.argument(i).to_number(global_object) : Value(fallback);
-    };
+    // 2. Let m be ? ToNumber(min).
+    auto minute = TRY(vm.argument(0).to_number(global_object));
 
-    auto& datetime = this_object->datetime();
+    // 3. If sec is not present, let s be SecFromTime(t); otherwise, let s be ? ToNumber(sec).
+    auto second = TRY(argument_or_value(global_object, 1, sec_from_time(time)));
 
-    auto new_minutes_value = TRY(vm.argument(0).to_number(global_object));
-    if (!new_minutes_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_minutes = new_minutes_value.as_i32();
+    // 4. If ms is not present, let milli be msFromTime(t); otherwise, let milli be ? ToNumber(ms).
+    auto millisecond = TRY(argument_or_value(global_object, 2, ms_from_time(time)));
 
-    auto new_seconds_value = TRY(arg_or(1, datetime.second()));
-    if (!new_seconds_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_seconds = new_seconds_value.as_i32();
+    // 5. Let date be MakeDate(Day(t), MakeTime(HourFromTime(t), m, s, milli)).
+    auto hour = Value(hour_from_time(time));
 
-    auto new_milliseconds_value = TRY(arg_or(2, this_object->milliseconds()));
-    if (!new_milliseconds_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_milliseconds = new_milliseconds_value.as_i32();
+    auto new_time = make_time(global_object, hour, minute, second, millisecond);
+    auto date = make_date(Value(day(time)), new_time);
 
-    new_seconds += new_milliseconds / 1000;
-    this_object->set_milliseconds(new_milliseconds % 1000);
+    // 6. Let u be TimeClip(UTC(date)).
+    date = time_clip(global_object, Value(utc_time(date.as_double())));
 
-    datetime.set_time(datetime.year(), datetime.month(), datetime.day(), datetime.hour(), new_minutes, new_seconds);
-    if (this_object->time() > Date::time_clip) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
+    // 7. Set the [[DateValue]] internal slot of this Date object to u.
+    auto* this_object = MUST(typed_this_object(global_object));
+    this_object->set_date_value(date.as_double());
 
-    this_object->set_is_invalid(false);
-    return Value(this_object->time());
+    // 8. Return u.
+    return date;
 }
 
 // 21.4.4.25 Date.prototype.setMonth ( month [ , date ] ), https://tc39.es/ecma262/#sec-date.prototype.setmonth
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_month)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be LocalTime(? thisTimeValue(this value)).
+    auto this_time = TRY(this_time_value(global_object, vm.this_value(global_object)));
+    auto time = local_time(this_time.as_double());
 
-    auto arg_or = [&vm, &global_object](size_t i, i32 fallback) -> ThrowCompletionOr<Value> {
-        return vm.argument_count() > i ? vm.argument(i).to_number(global_object) : Value(fallback);
-    };
+    // 2. Let m be ? ToNumber(month).
+    auto month = TRY(vm.argument(0).to_number(global_object));
 
-    auto& datetime = this_object->datetime();
+    // 3. If date is not present, let dt be DateFromTime(t); otherwise, let dt be ? ToNumber(date).
+    auto date = TRY(argument_or_value(global_object, 1, date_from_time(time)));
 
-    auto new_month_value = TRY(vm.argument(0).to_number(global_object));
-    if (!new_month_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_month = new_month_value.as_i32() + 1; // JS Months: 0 - 11, DateTime months: 1-12
+    // 4. Let newDate be MakeDate(MakeDay(YearFromTime(t), m, dt), TimeWithinDay(t)).
+    auto year = Value(year_from_time(time));
 
-    auto new_date_value = TRY(arg_or(1, this_object->date()));
-    if (!new_date_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_date = new_date_value.as_i32();
+    auto day = make_day(global_object, year, month, date);
+    auto new_date = make_date(day, Value(time_within_day(time)));
 
-    datetime.set_time(datetime.year(), new_month, new_date, datetime.hour(), datetime.minute(), datetime.second());
-    if (this_object->time() > Date::time_clip) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
+    // 5. Let u be TimeClip(UTC(newDate)).
+    new_date = time_clip(global_object, Value(utc_time(new_date.as_double())));
 
-    this_object->set_is_invalid(false);
-    return Value(this_object->time());
+    // 6. Set the [[DateValue]] internal slot of this Date object to u.
+    auto* this_object = MUST(typed_this_object(global_object));
+    this_object->set_date_value(new_date.as_double());
+
+    // 7. Return u.
+    return new_date;
 }
 
 // 21.4.4.26 Date.prototype.setSeconds ( sec [ , ms ] ), https://tc39.es/ecma262/#sec-date.prototype.setseconds
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_seconds)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be LocalTime(? thisTimeValue(this value)).
+    auto this_time = TRY(this_time_value(global_object, vm.this_value(global_object)));
+    auto time = local_time(this_time.as_double());
 
-    auto arg_or = [&vm, &global_object](size_t i, i32 fallback) -> ThrowCompletionOr<Value> {
-        return vm.argument_count() > i ? vm.argument(i).to_number(global_object) : Value(fallback);
-    };
+    // 2. Let s be ? ToNumber(sec).
+    auto second = TRY(vm.argument(0).to_number(global_object));
 
-    auto& datetime = this_object->datetime();
+    // 3. If ms is not present, let milli be msFromTime(t); otherwise, let milli be ? ToNumber(ms).
+    auto millisecond = TRY(argument_or_value(global_object, 1, ms_from_time(time)));
 
-    auto new_seconds_value = TRY(vm.argument(0).to_number(global_object));
-    if (!new_seconds_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_seconds = new_seconds_value.as_i32();
+    // 4. Let date be MakeDate(Day(t), MakeTime(HourFromTime(t), MinFromTime(t), s, milli)).
+    auto hour = Value(hour_from_time(time));
+    auto minute = Value(min_from_time(time));
 
-    auto new_milliseconds_value = TRY(arg_or(1, this_object->milliseconds()));
-    if (!new_milliseconds_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_milliseconds = new_milliseconds_value.as_i32();
+    auto new_time = make_time(global_object, hour, minute, second, millisecond);
+    auto new_date = make_date(Value(day(time)), new_time);
 
-    new_seconds += new_milliseconds / 1000;
-    this_object->set_milliseconds(new_milliseconds % 1000);
+    // 5. Let u be TimeClip(UTC(date)).
+    new_date = time_clip(global_object, Value(utc_time(new_date.as_double())));
 
-    datetime.set_time(datetime.year(), datetime.month(), datetime.day(), datetime.hour(), datetime.minute(), new_seconds);
-    if (this_object->time() > Date::time_clip) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
+    // 6. Set the [[DateValue]] internal slot of this Date object to u.
+    auto* this_object = MUST(typed_this_object(global_object));
+    this_object->set_date_value(new_date.as_double());
 
-    this_object->set_is_invalid(false);
-    return Value(this_object->time());
+    // 7. Return u.
+    return new_date;
 }
 
 // 21.4.4.27 Date.prototype.setTime ( time ), https://tc39.es/ecma262/#sec-date.prototype.settime
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_time)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Perform ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    auto new_time_value = TRY(vm.argument(0).to_number(global_object));
-    if (!new_time_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_time = new_time_value.as_double();
+    // 2. Let t be ? ToNumber(time).
+    time = TRY(vm.argument(0).to_number(global_object));
 
-    if (new_time > Date::time_clip) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
+    // 3. Let v be TimeClip(t).
+    time = time_clip(global_object, time);
 
-    auto new_date_time = Core::DateTime::from_timestamp(static_cast<time_t>(new_time / 1000));
-    this_object->datetime().set_time(new_date_time.year(), new_date_time.month(), new_date_time.day(), new_date_time.hour(), new_date_time.minute(), new_date_time.second());
-    this_object->set_milliseconds(static_cast<i16>(fmod(new_time, 1000)));
+    // 4. Set the [[DateValue]] internal slot of this Date object to v.
+    auto* this_object = MUST(typed_this_object(global_object));
+    this_object->set_date_value(time.as_double());
 
-    this_object->set_is_invalid(false);
-    return Value(this_object->time());
+    // 5. Return v.
+    return time;
 }
 
 // 21.4.4.35 Date.prototype.toDateString ( ), https://tc39.es/ecma262/#sec-date.prototype.todatestring
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_date_string)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let O be this Date object.
+    // 2. Let tv be ? thisTimeValue(O).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_string(vm, "Invalid Date");
+    // 3. If tv is NaN, return "Invalid Date".
+    if (time.is_nan())
+        return js_string(vm, "Invalid Date"sv);
 
-    auto string = this_object->date_string();
-    return js_string(vm, move(string));
+    // 4. Let t be LocalTime(tv).
+    // 5. Return DateString(t).
+    return js_string(vm, date_string(local_time(time.as_double())));
 }
 
 // 21.4.4.36 Date.prototype.toISOString ( ), https://tc39.es/ecma262/#sec-date.prototype.toisostring
@@ -632,7 +638,7 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_iso_string)
 {
     auto* this_object = TRY(typed_this_object(global_object));
 
-    if (this_object->is_invalid())
+    if (!Value(this_object->date_value()).is_finite_number())
         return vm.throw_completion<RangeError>(global_object, ErrorType::InvalidTimeValue);
 
     auto string = this_object->iso_date_string();
@@ -740,13 +746,11 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_locale_time_string)
 // 21.4.4.41 Date.prototype.toString ( ), https://tc39.es/ecma262/#sec-date.prototype.tostring
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_string)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
-
-    if (this_object->is_invalid())
-        return js_string(vm, "Invalid Date");
+    // 1. Let tv be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    auto string = this_object->string();
-    return js_string(vm, move(string));
+    // 2. Return ToDateString(tv).
+    return js_string(vm, JS::to_date_string(time.as_double()));
 }
 
 // 21.4.4.41.1 TimeString ( tv ), https://tc39.es/ecma262/#sec-timestring
@@ -861,25 +865,52 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_temporal_instant)
 // 21.4.4.42 Date.prototype.toTimeString ( ), https://tc39.es/ecma262/#sec-date.prototype.totimestring
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_time_string)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let O be this Date object.
+    // 2. Let tv be ? thisTimeValue(O).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_string(vm, "Invalid Date");
+    // 3. If tv is NaN, return "Invalid Date".
+    if (time.is_nan())
+        return js_string(vm, "Invalid Date"sv);
 
-    auto string = this_object->time_string();
+    // 4. Let t be LocalTime(tv).
+    // 5. Return the string-concatenation of TimeString(t) and TimeZoneString(tv).
+    auto string = String::formatted("{}{}", time_string(local_time(time.as_double())), time_zone_string(time.as_double()));
     return js_string(vm, move(string));
 }
 
 // 21.4.4.43 Date.prototype.toUTCString ( ), https://tc39.es/ecma262/#sec-date.prototype.toutcstring
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_utc_string)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let O be this Date object.
+    // 2. Let tv be ? thisTimeValue(O).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_string(vm, "Invalid Date");
+    // 3. If tv is NaN, return "Invalid Date".
+    if (time.is_nan())
+        return js_string(vm, "Invalid Date"sv);
 
-    // HTTP dates are always expressed in GMT.
-    auto string = this_object->gmt_date_string();
+    // 4. Let weekday be the Name of the entry in Table 62 with the Number WeekDay(tv).
+    auto weekday = day_names[week_day(time.as_double())];
+
+    // 5. Let month be the Name of the entry in Table 63 with the Number MonthFromTime(tv).
+    auto month = month_names[month_from_time(time.as_double())];
+
+    // 6. Let day be the String representation of DateFromTime(tv), formatted as a two-digit decimal number, padded to the left with the code unit 0x0030 (DIGIT ZERO) if necessary.
+    auto day = date_from_time(time.as_double());
+
+    // 7. Let yv be YearFromTime(tv).
+    auto year = year_from_time(time.as_double());
+
+    // 8. If yv ≥ +0𝔽, let yearSign be the empty String; otherwise, let yearSign be "-".
+    auto year_sign = year >= 0 ? ""sv : "-"sv;
+
+    // 9. Let year be the String representation of abs(ℝ(yv)), formatted as a decimal number.
+    year = abs(year);
+
+    // 10. Let paddedYear be ! StringPad(year, 4𝔽, "0", start).
+    // 11. Return the string-concatenation of weekday, ",", the code unit 0x0020 (SPACE), day, the code unit 0x0020 (SPACE), month, the code unit 0x0020 (SPACE), yearSign, paddedYear, the code unit 0x0020 (SPACE), and TimeString(tv).
+    auto string = String::formatted("{}, {:02} {} {}{:04} {}", weekday, day, month, year_sign, year, time_string(time.as_double()));
     return js_string(vm, move(string));
 }
 
@@ -906,39 +937,62 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::symbol_to_primitive)
 // B.2.4.1 Date.prototype.getYear ( ), https://tc39.es/ecma262/#sec-date.prototype.getyear
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_year)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    if (this_object->is_invalid())
-        return js_nan();
+    // 2. If t is NaN, return NaN.
+    if (time.is_nan())
+        return time;
 
-    return Value(this_object->year() - 1900);
+    // 3. Return Return YearFromTime(LocalTime(t)) - 1900𝔽.
+    return Value(year_from_time(local_time(time.as_double())) - 1900);
 }
 
 // B.2.4.2 Date.prototype.setYear ( year ), https://tc39.es/ecma262/#sec-date.prototype.setyear
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_year)
 {
-    auto* this_object = TRY(typed_this_object(global_object));
+    // 1. Let t be ? thisTimeValue(this value).
+    auto this_time = TRY(this_time_value(global_object, vm.this_value(global_object)));
 
-    auto& datetime = this_object->datetime();
+    // 2. If t is NaN, set t to +0𝔽; otherwise, set t to LocalTime(t).
+    double time = 0;
+    if (!this_time.is_nan())
+        time = local_time(this_time.as_double());
 
-    auto new_year_value = TRY(vm.argument(0).to_number(global_object));
-    if (!new_year_value.is_finite_number()) {
-        this_object->set_is_invalid(true);
-        return js_nan();
-    }
-    auto new_year = new_year_value.as_i32();
-    if (new_year >= 0 && new_year <= 99)
-        new_year += 1900;
+    // 3. Let y be ? ToNumber(year).
+    auto year = TRY(vm.argument(0).to_number(global_object));
 
-    datetime.set_time(new_year, datetime.month(), datetime.day(), datetime.hour(), datetime.minute(), datetime.second());
-    if (this_object->time() > Date::time_clip) {
-        this_object->set_is_invalid(true);
-        return js_nan();
+    auto* this_object = MUST(typed_this_object(global_object));
+
+    // 4. If y is NaN, then
+    if (year.is_nan()) {
+        // a. Set the [[DateValue]] internal slot of this Date object to NaN.
+        this_object->set_date_value(js_nan().as_double());
+
+        // b. Return NaN.
+        return year;
     }
 
-    this_object->set_is_invalid(false);
+    // 5. Let yi be ! ToIntegerOrInfinity(y).
+    auto year_double = MUST(year.to_integer_or_infinity(global_object));
+
+    // 6. If 0 ≤ yi ≤ 99, let yyyy be 1900𝔽 + 𝔽(yi).
+    if (0 <= year_double && year_double <= 99)
+        year = Value(1900 + year_double);
+    // 7. Else, let yyyy be y.
+
+    // 8. Let d be MakeDay(yyyy, MonthFromTime(t), DateFromTime(t)).
+    auto day = make_day(global_object, year, Value(month_from_time(time)), Value(date_from_time(time)));
+
+    // 9. Let date be UTC(MakeDate(d, TimeWithinDay(t))).
+    auto date = utc_time(make_date(day, Value(time_within_day(time))).as_double());
+
+    // 10. Set the [[DateValue]] internal slot of this Date object to TimeClip(date).
+    auto new_date = time_clip(global_object, Value(date));
+    this_object->set_date_value(new_date.as_double());
 
-    return Value(this_object->time());
+    // 11. Return the value of the [[DateValue]] internal slot of this Date object.
+    return new_date;
 }
 
 // B.2.4.3 Date.prototype.toGMTString ( ), https://tc39.es/ecma262/#sec-date.prototype.togmtstring
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setDate.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setDate.js
index b8cd57710f..fc7807eaa4 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setDate.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setDate.js
@@ -30,18 +30,3 @@ test("Day as argument", () => {
     expect(date.getSeconds()).toBe(0);
     expect(date.getMilliseconds()).toBe(0);
 });
-
-test("Make Invalid Date valid again", () => {
-    let date = new Date(2021, 0, 1);
-    date.setDate(NaN);
-    expect(date.getTime()).toBe(NaN);
-
-    date.setDate(16);
-    expect(date.getFullYear()).toBe(2021);
-    expect(date.getMonth()).toBe(0);
-    expect(date.getDate()).toBe(16);
-    expect(date.getHours()).toBe(0);
-    expect(date.getMinutes()).toBe(0);
-    expect(date.getSeconds()).toBe(0);
-    expect(date.getMilliseconds()).toBe(0);
-});
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMonth.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMonth.js
index a7ffee3c01..1ae040d833 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMonth.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMonth.js
@@ -60,28 +60,4 @@ test("NaN or undefined in any arguments", () => {
     date = new Date(2021, 0, 1);
     date.setMonth(2021, undefined);
     expect(date.getTime()).toBe(NaN);
-
-    date.setMonth(3, 16);
-    expect(date.getFullYear()).toBe(2021);
-    expect(date.getMonth()).toBe(3);
-    expect(date.getDate()).toBe(16);
-    expect(date.getHours()).toBe(0);
-    expect(date.getMinutes()).toBe(0);
-    expect(date.getSeconds()).toBe(0);
-    expect(date.getMilliseconds()).toBe(0);
-});
-
-test("Make Invalid Date valid again", () => {
-    let date = new Date(2021, 0, 1);
-    date.setMonth(NaN, 3, 16);
-    expect(date.getTime()).toBe(NaN);
-
-    date.setMonth(3, 16);
-    expect(date.getFullYear()).toBe(2021);
-    expect(date.getMonth()).toBe(3);
-    expect(date.getDate()).toBe(16);
-    expect(date.getHours()).toBe(0);
-    expect(date.getMinutes()).toBe(0);
-    expect(date.getSeconds()).toBe(0);
-    expect(date.getMilliseconds()).toBe(0);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleDateString.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleDateString.js
index 8eb8c324b2..387f5b0291 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleDateString.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleDateString.js
@@ -15,12 +15,6 @@ describe("errors", () => {
         }).toThrowWithMessage(TypeError, "Cannot convert BigInt to number");
     });
 
-    test("time value cannot be clipped", () => {
-        expect(() => {
-            new Date(-8.65e15).toLocaleDateString();
-        }).toThrowWithMessage(RangeError, "Time value must be between -8.64E15 and 8.64E15");
-    });
-
     test("timeStyle may not be specified", () => {
         expect(() => {
             new Date().toLocaleDateString([], { timeStyle: "short" });
@@ -34,6 +28,11 @@ describe("correct behavior", () => {
         expect(d.toLocaleDateString()).toBe("Invalid Date");
     });
 
+    test("time clip", () => {
+        const d = new Date(-8.65e15);
+        expect(d.toLocaleDateString()).toBe("Invalid Date");
+    });
+
     const d0 = new Date(Date.UTC(2021, 11, 7, 17, 40, 50, 456));
     const d1 = new Date(Date.UTC(1989, 0, 23, 7, 8, 9, 45));
 
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleString.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleString.js
index dc76c7f6a9..bb2bc638be 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleString.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleString.js
@@ -14,12 +14,6 @@ describe("errors", () => {
             new Date(1n).toLocaleString();
         }).toThrowWithMessage(TypeError, "Cannot convert BigInt to number");
     });
-
-    test("time value cannot be clipped", () => {
-        expect(() => {
-            new Date(-8.65e15).toLocaleString();
-        }).toThrowWithMessage(RangeError, "Time value must be between -8.64E15 and 8.64E15");
-    });
 });
 
 describe("correct behavior", () => {
@@ -28,6 +22,11 @@ describe("correct behavior", () => {
         expect(d.toLocaleString()).toBe("Invalid Date");
     });
 
+    test("time clip", () => {
+        const d = new Date(-8.65e15);
+        expect(d.toLocaleString()).toBe("Invalid Date");
+    });
+
     const d0 = new Date(Date.UTC(2021, 11, 7, 17, 40, 50, 456));
     const d1 = new Date(Date.UTC(1989, 0, 23, 7, 8, 9, 45));
 
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleTimeString.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleTimeString.js
index 6d85632f8e..d188994039 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleTimeString.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleTimeString.js
@@ -15,12 +15,6 @@ describe("errors", () => {
         }).toThrowWithMessage(TypeError, "Cannot convert BigInt to number");
     });
 
-    test("time value cannot be clipped", () => {
-        expect(() => {
-            new Date(-8.65e15).toLocaleTimeString();
-        }).toThrowWithMessage(RangeError, "Time value must be between -8.64E15 and 8.64E15");
-    });
-
     test("dateStyle may not be specified", () => {
         expect(() => {
             new Date().toLocaleTimeString([], { dateStyle: "short" });
@@ -34,6 +28,11 @@ describe("correct behavior", () => {
         expect(d.toLocaleTimeString()).toBe("Invalid Date");
     });
 
+    test("time clip", () => {
+        const d = new Date(-8.65e15);
+        expect(d.toLocaleTimeString()).toBe("Invalid Date");
+    });
+
     const d0 = new Date(Date.UTC(2021, 11, 7, 17, 40, 50, 456));
     const d1 = new Date(Date.UTC(1989, 0, 23, 7, 8, 9, 45));