LibJS Date: Added "Invalid Date".

Setting an invalid value on a Date object now makes it invalid.
Setting it again but with correct values makes it valid again.

29 files changed, 486 insertions, 85 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/Date.cpp b/Userland/Libraries/LibJS/Runtime/Date.cpp
index 8644de4ad0..8b65c8db4c 100644
--- a/Userland/Libraries/LibJS/Runtime/Date.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Date.cpp
@@ -32,15 +32,16 @@
 
 namespace JS {
 
-Date* Date::create(GlobalObject& global_object, Core::DateTime datetime, u16 milliseconds)
+Date* Date::create(GlobalObject& global_object, Core::DateTime datetime, u16 milliseconds, bool is_invalid)
 {
-    return global_object.heap().allocate<Date>(global_object, datetime, milliseconds, *global_object.date_prototype());
+    return global_object.heap().allocate<Date>(global_object, datetime, milliseconds, is_invalid, *global_object.date_prototype());
 }
 
-Date::Date(Core::DateTime datetime, u16 milliseconds, Object& prototype)
+Date::Date(Core::DateTime datetime, u16 milliseconds, bool is_invalid, Object& prototype)
     : Object(prototype)
     , m_datetime(datetime)
     , m_milliseconds(milliseconds)
+    , m_is_invalid(is_invalid)
 {
 }
 
diff --git a/Userland/Libraries/LibJS/Runtime/Date.h b/Userland/Libraries/LibJS/Runtime/Date.h
index 11f50531aa..ffc68faa75 100644
--- a/Userland/Libraries/LibJS/Runtime/Date.h
+++ b/Userland/Libraries/LibJS/Runtime/Date.h
@@ -35,9 +35,9 @@ class Date final : public Object {
     JS_OBJECT(Date, Object);
 
 public:
-    static Date* create(GlobalObject&, Core::DateTime, u16 milliseconds);
+    static Date* create(GlobalObject&, Core::DateTime, u16 milliseconds, bool is_invalid = false);
 
-    Date(Core::DateTime datetime, u16 milliseconds, Object& prototype);
+    Date(Core::DateTime datetime, u16 milliseconds, bool is_invalid, Object& prototype);
     virtual ~Date() override;
 
     Core::DateTime& datetime() { return m_datetime; }
@@ -54,6 +54,9 @@ public:
     double time() const { return datetime().timestamp() * 1000.0 + milliseconds(); }
     int year() const { return datetime().day(); }
 
+    bool is_invalid() const { return m_is_invalid; }
+    void set_is_invalid(bool value) { m_is_invalid = value; }
+
     int utc_date() const;
     int utc_day() const;
     int utc_full_year() const;
@@ -73,6 +76,9 @@ public:
     String time_string() const { return m_datetime.to_string("%T GMT+0000 (UTC)"); }
     String string() const
     {
+        if (is_invalid())
+            return "Invalid Date";
+
         return String::formatted("{} {}", date_string(), time_string());
     }
 
@@ -94,6 +100,7 @@ private:
 
     Core::DateTime m_datetime;
     u16 m_milliseconds;
+    bool m_is_invalid { false };
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/DateConstructor.cpp b/Userland/Libraries/LibJS/Runtime/DateConstructor.cpp
index d38101c8a8..093acbe140 100644
--- a/Userland/Libraries/LibJS/Runtime/DateConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/DateConstructor.cpp
@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2020, Linus Groh <mail@linusgroh.de>
  * Copyright (c) 2020, Nico Weber <thakis@chromium.org>
+ * Copyright (c) 2021, Petróczi Zoltán <petroczizoltan@tutanota.com>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -176,30 +177,92 @@ Value DateConstructor::construct(Function&)
         auto milliseconds = static_cast<u16>(tv.tv_usec / 1000);
         return Date::create(global_object(), datetime, milliseconds);
     }
+
+    auto create_invalid_date = [this]() {
+        auto datetime = Core::DateTime::from_timestamp(static_cast<time_t>(0));
+        auto milliseconds = static_cast<u16>(0);
+        return Date::create(global_object(), datetime, milliseconds, true);
+    };
+
     if (vm.argument_count() == 1) {
         auto value = vm.argument(0);
         if (value.is_string())
             value = parse_simplified_iso8601(value.as_string().string());
-        // A timestamp since the epoch, in UTC.
-        // FIXME: This doesn't construct an "Invalid Date" object if the argument is NaN.
-        // FIXME: Date() probably should use a double as internal representation, so that NaN arguments and larger offsets are handled correctly.
-        double value_as_double = value.to_double(global_object());
+        else
+            value = value.to_number(global_object());
+
         if (vm.exception())
             return {};
+
+        if (!value.is_finite_number()) {
+            return create_invalid_date();
+        }
+
+        // A timestamp since the epoch, in UTC.
+        double value_as_double = value.as_double();
         auto datetime = Core::DateTime::from_timestamp(static_cast<time_t>(value_as_double / 1000));
         auto milliseconds = static_cast<u16>(fmod(value_as_double, 1000));
         return Date::create(global_object(), datetime, milliseconds);
     }
+
     // A date/time in components, in local time.
-    // FIXME: This doesn't construct an "Invalid Date" object if one of the arguments is NaN.
-    auto arg_or = [this, &vm](size_t i, i32 fallback) { return vm.argument_count() > i ? vm.argument(i).to_i32(global_object()) : fallback; };
-    int year = vm.argument(0).to_i32(global_object());
-    int month_index = vm.argument(1).to_i32(global_object());
-    int day = arg_or(2, 1);
-    int hours = arg_or(3, 0);
-    int minutes = arg_or(4, 0);
-    int seconds = arg_or(5, 0);
-    int milliseconds = arg_or(6, 0);
+    auto arg_or = [&vm, this](size_t i, i32 fallback) { return vm.argument_count() > i ? vm.argument(i).to_number(global_object()) : Value(fallback); };
+
+    auto year_value = vm.argument(0).to_number(global_object());
+    if (vm.exception())
+        return {};
+    if (!year_value.is_finite_number()) {
+        return create_invalid_date();
+    }
+    auto year = year_value.as_i32();
+
+    auto month_index_value = vm.argument(1).to_number(global_object());
+    if (vm.exception())
+        return {};
+    if (!month_index_value.is_finite_number()) {
+        return create_invalid_date();
+    }
+    auto month_index = month_index_value.as_i32();
+
+    auto day_value = arg_or(2, 1);
+    if (vm.exception())
+        return {};
+    if (!day_value.is_finite_number()) {
+        return create_invalid_date();
+    }
+    auto day = day_value.as_i32();
+
+    auto hours_value = arg_or(3, 0);
+    if (vm.exception())
+        return {};
+    if (!hours_value.is_finite_number()) {
+        return create_invalid_date();
+    }
+    auto hours = hours_value.as_i32();
+
+    auto minutes_value = arg_or(4, 0);
+    if (vm.exception())
+        return {};
+    if (!minutes_value.is_finite_number()) {
+        return create_invalid_date();
+    }
+    auto minutes = minutes_value.as_i32();
+
+    auto seconds_value = arg_or(5, 0);
+    if (vm.exception())
+        return {};
+    if (!seconds_value.is_finite_number()) {
+        return create_invalid_date();
+    }
+    auto seconds = seconds_value.as_i32();
+
+    auto milliseconds_value = arg_or(6, 0);
+    if (vm.exception())
+        return {};
+    if (!milliseconds_value.is_finite_number()) {
+        return create_invalid_date();
+    }
+    auto milliseconds = milliseconds_value.as_i32();
 
     seconds += milliseconds / 1000;
     milliseconds %= 1000;
diff --git a/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp b/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
index 2d98bf6adf..f3fc6dbb30 100644
--- a/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, Linus Groh <mail@linusgroh.de>
+ * Copyright (c) 2021, Petróczi Zoltán <petroczizoltan@tutanota.com>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -106,6 +107,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_date)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->date()));
 }
 
@@ -114,6 +119,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_day)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->day()));
 }
 
@@ -122,6 +131,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_full_year)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->full_year()));
 }
 
@@ -130,32 +143,42 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_full_year)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
-    auto new_year = vm.argument(0).to_i32(global_object);
-    if (vm.exception())
-        return {};
 
     auto& datetime = this_object->datetime();
 
-    i32 new_month;
-    if (vm.argument_count() >= 2) {
-        new_month = vm.argument(1).to_i32(global_object);
-        if (vm.exception())
-            return {};
-    } else {
-        new_month = datetime.month();
+    auto arg_or = [&vm, &global_object](size_t i, i32 fallback) { return vm.argument_count() > i ? vm.argument(i).to_number(global_object) : Value(fallback); };
+
+    auto new_year_value = vm.argument(0).to_number(global_object);
+    if (vm.exception())
+        return {};
+    if (!new_year_value.is_finite_number()) {
+        this_object->set_is_invalid(true);
+        return js_nan();
     }
+    auto new_year = new_year_value.as_i32();
 
-    i32 new_day;
-    if (vm.argument_count() >= 3) {
-        new_day = vm.argument(2).to_i32(global_object);
-        if (vm.exception())
-            return {};
-    } else {
-        new_day = datetime.day();
+    auto new_month_value = arg_or(1, datetime.month());
+    if (vm.exception())
+        return {};
+    if (!new_month_value.is_finite_number()) {
+        this_object->set_is_invalid(true);
+        return js_nan();
     }
+    auto new_month = new_month_value.as_i32();
+
+    auto new_day_value = arg_or(2, datetime.day());
+    if (vm.exception())
+        return {};
+    if (!new_day_value.is_finite_number()) {
+        this_object->set_is_invalid(true);
+        return js_nan();
+    }
+    auto new_day = new_day_value.as_i32();
 
     datetime.set_time(new_year, new_month, new_day, datetime.hour(), datetime.minute(), datetime.second());
-    return Value(this_object->time());
+    this_object->set_is_invalid(false);
+
+    return Value { this_object->time() };
 }
 
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_hours)
@@ -163,6 +186,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_hours)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->hours()));
 }
 
@@ -172,37 +199,50 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_hours)
     if (!this_object)
         return {};
 
-    auto new_hours = vm.argument(0).to_i32(global_object);
-    if (vm.exception())
-        return {};
+    auto arg_or = [&vm, &global_object](size_t i, i32 fallback) { return vm.argument_count() > i ? vm.argument(i).to_number(global_object) : Value(fallback); };
 
     auto& datetime = this_object->datetime();
 
-    i32 new_minutes;
-    if (vm.argument_count() >= 2) {
-        new_minutes = vm.argument(1).to_i32(global_object);
-        if (vm.exception())
-            return {};
-    } else {
-        new_minutes = datetime.minute();
+    auto new_hours_value = vm.argument(0).to_number(global_object);
+    if (vm.exception())
+        return {};
+    if (!new_hours_value.is_finite_number()) {
+        this_object->set_is_invalid(true);
+        return js_nan();
     }
+    auto new_hours = new_hours_value.as_i32();
 
-    i32 new_seconds;
-    if (vm.argument_count() >= 3) {
-        new_seconds = vm.argument(2).to_i32(global_object);
-        if (vm.exception())
-            return {};
-    } else {
-        new_seconds = datetime.second();
+    auto new_minutes_value = arg_or(1, datetime.minute());
+    if (vm.exception())
+        return {};
+    if (!new_minutes_value.is_finite_number()) {
+        this_object->set_is_invalid(true);
+        return js_nan();
     }
+    auto new_minutes = new_minutes_value.as_i32();
 
-    if (vm.argument_count() >= 4) {
-        auto new_milliseconds = vm.argument(3).to_i32(global_object);
-        if (vm.exception())
-            return {};
-        new_seconds += new_milliseconds / 1000;
-        this_object->set_milliseconds(new_milliseconds % 1000);
+    auto new_seconds_value = arg_or(2, datetime.second());
+    if (vm.exception())
+        return {};
+    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 = arg_or(3, this_object->milliseconds());
+    if (vm.exception())
+        return {};
+    if (!new_milliseconds_value.is_finite_number()) {
+        this_object->set_is_invalid(true);
+        return js_nan();
+    }
+    auto new_milliseconds = new_milliseconds_value.as_i32();
+
+    this_object->set_is_invalid(false);
+
+    new_seconds += new_milliseconds / 1000;
+    this_object->set_milliseconds(new_milliseconds % 1000);
 
     datetime.set_time(datetime.year(), datetime.month(), datetime.day(), new_hours, new_minutes, new_seconds);
     return Value(this_object->time());
@@ -213,6 +253,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_milliseconds)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->milliseconds()));
 }
 
@@ -222,10 +266,17 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_milliseconds)
     if (!this_object)
         return {};
 
-    auto new_milliseconds = vm.argument(0).to_i32(global_object);
+    auto new_milliseconds_value = vm.argument(0).to_number(global_object);
     if (vm.exception())
         return {};
 
+    if (!new_milliseconds_value.is_finite_number()) {
+        this_object->set_is_invalid(true);
+        return js_nan();
+    }
+
+    auto new_milliseconds = new_milliseconds_value.as_i32();
+
     this_object->set_milliseconds(new_milliseconds % 1000);
 
     auto added_seconds = new_milliseconds / 1000;
@@ -234,6 +285,8 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_milliseconds)
         datetime.set_time(datetime.year(), datetime.month(), datetime.day(), datetime.hour(), datetime.minute(), datetime.second() + added_seconds);
     }
 
+    this_object->set_is_invalid(false);
+
     return Value(this_object->time());
 }
 
@@ -242,6 +295,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_minutes)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->minutes()));
 }
 
@@ -251,28 +308,41 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_minutes)
     if (!this_object)
         return {};
 
-    auto new_minutes = vm.argument(0).to_i32(global_object);
-    if (vm.exception())
-        return {};
+    auto arg_or = [&vm, &global_object](size_t i, i32 fallback) { return vm.argument_count() > i ? vm.argument(i).to_number(global_object) : Value(fallback); };
 
     auto& datetime = this_object->datetime();
 
-    i32 new_seconds;
-    if (vm.argument_count() >= 2) {
-        new_seconds = vm.argument(1).to_i32(global_object);
-        if (vm.exception())
-            return {};
-    } else {
-        new_seconds = datetime.second();
+    auto new_minutes_value = vm.argument(0).to_number(global_object);
+    if (vm.exception())
+        return {};
+    if (!new_minutes_value.is_finite_number()) {
+        this_object->set_is_invalid(true);
+        return js_nan();
     }
+    auto new_minutes = new_minutes_value.as_i32();
 
-    if (vm.argument_count() >= 3) {
-        auto new_milliseconds = vm.argument(2).to_i32(global_object);
-        if (vm.exception())
-            return {};
-        new_seconds += new_milliseconds / 1000;
-        this_object->set_milliseconds(new_milliseconds % 1000);
+    auto new_seconds_value = arg_or(1, datetime.second());
+    if (vm.exception())
+        return {};
+    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 = arg_or(2, this_object->milliseconds());
+    if (vm.exception())
+        return {};
+    if (!new_milliseconds_value.is_finite_number()) {
+        this_object->set_is_invalid(true);
+        return js_nan();
+    }
+    auto new_milliseconds = new_milliseconds_value.as_i32();
+
+    this_object->set_is_invalid(false);
+
+    new_seconds += new_milliseconds / 1000;
+    this_object->set_milliseconds(new_milliseconds % 1000);
 
     datetime.set_time(datetime.year(), datetime.month(), datetime.day(), datetime.hour(), new_minutes, new_seconds);
     return Value(this_object->time());
@@ -283,6 +353,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_month)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->month()));
 }
 
@@ -291,6 +365,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_seconds)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->seconds()));
 }
 
@@ -300,19 +378,32 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_seconds)
     if (!this_object)
         return {};
 
-    auto new_seconds = vm.argument(0).to_i32(global_object);
+    auto arg_or = [&vm, &global_object](size_t i, i32 fallback) { return vm.argument_count() > i ? vm.argument(i).to_number(global_object) : Value(fallback); };
+
+    auto& datetime = this_object->datetime();
+
+    auto new_seconds_value = vm.argument(0).to_number(global_object);
     if (vm.exception())
         return {};
+    if (!new_seconds_value.is_finite_number()) {
+        this_object->set_is_invalid(true);
+        return js_nan();
+    }
+    auto new_seconds = new_seconds_value.as_i32();
 
-    if (vm.argument_count() >= 2) {
-        auto new_milliseconds = vm.argument(1).to_i32(global_object);
-        if (vm.exception())
-            return {};
-        new_seconds += new_milliseconds / 1000;
-        this_object->set_milliseconds(new_milliseconds % 1000);
+    auto new_milliseconds_value = arg_or(1, this_object->milliseconds());
+    if (vm.exception())
+        return {};
+    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& datetime = this_object->datetime();
+    this_object->set_is_invalid(false);
+
+    new_seconds += new_milliseconds / 1000;
+    this_object->set_milliseconds(new_milliseconds % 1000);
 
     datetime.set_time(datetime.year(), datetime.month(), datetime.day(), datetime.hour(), datetime.minute(), new_seconds);
     return Value(this_object->time());
@@ -323,6 +414,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_time)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(this_object->time());
 }
 
@@ -331,6 +426,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_date)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->utc_date()));
 }
 
@@ -339,6 +438,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_day)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->utc_day()));
 }
 
@@ -347,6 +450,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_full_year)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->utc_full_year()));
 }
 
@@ -355,6 +462,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_hours)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->utc_hours()));
 }
 
@@ -363,6 +474,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_milliseconds)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->utc_milliseconds()));
 }
 
@@ -371,6 +486,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_month)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->utc_month()));
 }
 
@@ -379,6 +498,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_minutes)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->utc_minutes()));
 }
 
@@ -387,6 +510,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::get_utc_seconds)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_nan();
+
     return Value(static_cast<double>(this_object->utc_seconds()));
 }
 
@@ -395,6 +522,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_date_string)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_string(vm, "Invalid Date");
+
     auto string = this_object->date_string();
     return js_string(vm, move(string));
 }
@@ -412,6 +543,9 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_utc_string)
     if (!this_object)
         return {};
 
+    if (this_object->is_invalid())
+        return js_string(vm, "Invalid Date");
+
     // HTTP dates are always expressed in GMT.
     auto string = this_object->gmt_date_string();
     return js_string(vm, move(string));
@@ -422,6 +556,12 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_iso_string)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid()) {
+        vm.throw_exception<RangeError>(global_object, ErrorType::InvalidTimeValue);
+        return {};
+    }
+
     auto string = this_object->iso_date_string();
     return js_string(vm, move(string));
 }
@@ -431,6 +571,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_locale_date_string)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_string(vm, "Invalid Date");
+
     // FIXME: Optional locales, options params.
     auto string = this_object->locale_date_string();
     return js_string(vm, move(string));
@@ -441,6 +585,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_locale_string)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_string(vm, "Invalid Date");
+
     // FIXME: Optional locales, options params.
     auto string = this_object->locale_string();
     return js_string(vm, move(string));
@@ -451,6 +599,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_locale_time_string)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_string(vm, "Invalid Date");
+
     // FIXME: Optional locales, options params.
     auto string = this_object->locale_time_string();
     return js_string(vm, move(string));
@@ -461,6 +613,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_time_string)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_string(vm, "Invalid Date");
+
     auto string = this_object->time_string();
     return js_string(vm, move(string));
 }
@@ -470,6 +626,10 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_string)
     auto* this_object = typed_this(vm, global_object);
     if (!this_object)
         return {};
+
+    if (this_object->is_invalid())
+        return js_string(vm, "Invalid Date");
+
     auto string = this_object->string();
     return js_string(vm, move(string));
 }
diff --git a/Userland/Libraries/LibJS/Runtime/ErrorTypes.h b/Userland/Libraries/LibJS/Runtime/ErrorTypes.h
index f55314261d..cadc118d16 100644
--- a/Userland/Libraries/LibJS/Runtime/ErrorTypes.h
+++ b/Userland/Libraries/LibJS/Runtime/ErrorTypes.h
@@ -51,6 +51,7 @@
     M(InvalidIndex, "Index must be a positive integer")                                                                                 \
     M(InvalidLeftHandAssignment, "Invalid left-hand side in assignment")                                                                \
     M(InvalidLength, "Invalid {} length")                                                                                               \
+    M(InvalidTimeValue, "Invalid time value")                                                                                           \
     M(InvalidRadix, "Radix must be an integer no less than 2, and no greater than 36")                                                  \
     M(IsNotA, "{} is not a {}")                                                                                                         \
     M(IsNotAEvaluatedFrom, "{} is not a {} (evaluated from '{}')")                                                                      \
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.js
index cc76212e22..5a1c30178f 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.js
@@ -24,6 +24,13 @@ test("timestamp constructor", () => {
     expect(date.getSeconds()).toBe(1);
     expect(date.getFullYear()).toBe(1970);
     expect(date.getMonth()).toBe(1); // Feb
+
+    date = new Date(NaN);
+    expect(date.getTime()).toBe(NaN);
+    date = new Date(undefined);
+    expect(date.getTime()).toBe(NaN);
+    date = new Date("");
+    expect(date.getTime()).toBe(NaN);
 });
 
 test("tuple constructor", () => {
@@ -52,6 +59,11 @@ test("tuple constructor", () => {
     let timestamp_upper_bound = 1577750400000; // 2019-12-31T00:00:00Z
     expect(date.getTime()).toBeGreaterThan(timestamp_lower_bound);
     expect(date.getTime()).toBeLessThan(timestamp_upper_bound);
+
+    date = new Date(NaN, 11, 15, 9, 16, 14, 123);
+    expect(date.getTime()).toBe(NaN);
+    date = new Date(2021, 11, 15, 9, 16, 14, undefined);
+    expect(date.getTime()).toBe(NaN);
 });
 
 test("tuple constructor overflow", () => {
@@ -65,7 +77,7 @@ test("tuple constructor overflow", () => {
     expect(date.getMilliseconds()).toBe(345);
     expect(date.getDay()).toBe(4);
 
-    let date = new Date(2019, -13, -33, -30, -70, -80, -2345);
+    date = new Date(2019, -13, -33, -30, -70, -80, -2345);
     expect(date.getFullYear()).toBe(2017);
     expect(date.getMonth()).toBe(9);
     expect(date.getDate()).toBe(26);
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getDate.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getDate.js
index 647e43a997..d234126373 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getDate.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getDate.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getDate()).not.toBeNaN();
     expect(d.getDate()).toBeGreaterThanOrEqual(1);
     expect(d.getDate()).toBeLessThanOrEqual(31);
+    expect(new Date(NaN).getDate()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getDay.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getDay.js
index 534efeeee5..8f2a8cb223 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getDay.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getDay.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getDay()).not.toBeNaN();
     expect(d.getDay()).toBeGreaterThanOrEqual(0);
     expect(d.getDay()).toBeLessThanOrEqual(6);
+    expect(new Date(NaN).getDay()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getFullYear.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getFullYear.js
index 3748e835cf..b50ff71d8d 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getFullYear.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getFullYear.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getFullYear()).not.toBeNaN();
     expect(d.getFullYear()).toBe(d.getFullYear());
     expect(d.getFullYear()).toBeGreaterThanOrEqual(2020);
+    expect(new Date(NaN).getFullYear()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getHours.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getHours.js
index 7e562288f2..10cbe8bea5 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getHours.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getHours.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getHours()).not.toBeNaN();
     expect(d.getHours()).toBeGreaterThanOrEqual(0);
     expect(d.getHours()).toBeLessThanOrEqual(23);
+    expect(new Date(NaN).getHours()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getMilliseconds.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getMilliseconds.js
index 90c686f729..90ea61b32b 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getMilliseconds.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getMilliseconds.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getMilliseconds()).not.toBeNaN();
     expect(d.getMilliseconds()).toBeGreaterThanOrEqual(0);
     expect(d.getMilliseconds()).toBeLessThanOrEqual(999);
+    expect(new Date(NaN).getMilliseconds()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getMinutes.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getMinutes.js
index 5b87b8251d..06bd7b5b43 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getMinutes.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getMinutes.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getMinutes()).not.toBeNaN();
     expect(d.getMinutes()).toBeGreaterThanOrEqual(0);
     expect(d.getMinutes()).toBeLessThanOrEqual(59);
+    expect(new Date(NaN).getMinutes()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getMonth.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getMonth.js
index 7d52866ce7..ad9722a538 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getMonth.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getMonth.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getMonth()).not.toBeNaN();
     expect(d.getMonth()).toBeGreaterThanOrEqual(0);
     expect(d.getMonth()).toBeLessThanOrEqual(11);
+    expect(new Date(NaN).getMonth()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getSeconds.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getSeconds.js
index df30881c9a..07f02a8850 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getSeconds.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getSeconds.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getSeconds()).not.toBeNaN();
     expect(d.getSeconds()).toBeGreaterThanOrEqual(0);
     expect(d.getSeconds()).toBeLessThanOrEqual(59);
+    expect(new Date(NaN).getSeconds()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getTime.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getTime.js
index b9ada6fcc9..c3397ff0ff 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getTime.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getTime.js
@@ -3,4 +3,5 @@ test("basic functionality", () => {
     expect(d.getTime()).toBe(d.getTime());
     expect(d.getTime()).not.toBeNaN();
     expect(d.getTime()).toBeGreaterThanOrEqual(1580000000000);
+    expect(new Date(NaN).getTime()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCDate.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCDate.js
index d207385bad..2d1820508c 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCDate.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCDate.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getUTCDate()).not.toBeNaN();
     expect(d.getUTCDate()).toBeGreaterThanOrEqual(1);
     expect(d.getUTCDate()).toBeLessThanOrEqual(31);
+    expect(new Date(NaN).getUTCDate()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCDay.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCDay.js
index aec696be4a..63ab17c558 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCDay.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCDay.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getUTCDay()).not.toBeNaN();
     expect(d.getUTCDay()).toBeGreaterThanOrEqual(0);
     expect(d.getUTCDay()).toBeLessThanOrEqual(6);
+    expect(new Date(NaN).getUTCDay()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCFullYear.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCFullYear.js
index 50336d8178..733408c22b 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCFullYear.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCFullYear.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getUTCFullYear()).not.toBeNaN();
     expect(d.getUTCFullYear()).toBe(d.getUTCFullYear());
     expect(d.getUTCFullYear()).toBeGreaterThanOrEqual(2020);
+    expect(new Date(NaN).getUTCFullYear()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCHours.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCHours.js
index 298ed178e5..9d9aa39942 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCHours.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCHours.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getUTCHours()).not.toBeNaN();
     expect(d.getUTCHours()).toBeGreaterThanOrEqual(0);
     expect(d.getUTCHours()).toBeLessThanOrEqual(23);
+    expect(new Date(NaN).getUTCHours()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCMilliseconds.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCMilliseconds.js
index f53ea70428..9abb0cc13a 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCMilliseconds.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCMilliseconds.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getUTCMilliseconds()).not.toBeNaN();
     expect(d.getUTCMilliseconds()).toBeGreaterThanOrEqual(0);
     expect(d.getUTCMilliseconds()).toBeLessThanOrEqual(999);
+    expect(new Date(NaN).getUTCMilliseconds()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCMinutes.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCMinutes.js
index 6b1146331c..d8a5a9b865 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCMinutes.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCMinutes.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getUTCMinutes()).not.toBeNaN();
     expect(d.getUTCMinutes()).toBeGreaterThanOrEqual(0);
     expect(d.getUTCMinutes()).toBeLessThanOrEqual(59);
+    expect(new Date(NaN).getUTCMinutes()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCMonth.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCMonth.js
index ed6ed64d97..48296f7084 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCMonth.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCMonth.js
@@ -6,6 +6,7 @@ test("basic functionality", () => {
     expect(d.getUTCMonth()).toBeLessThanOrEqual(11);
 
     expect(new Date(Date.UTC(2020, 11)).getUTCMonth()).toBe(11);
+    expect(new Date(NaN).getUTCMonth()).toBe(NaN);
 });
 
 test("leap years", () => {
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCSeconds.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCSeconds.js
index d087a3c4c8..9a9f5d3e19 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCSeconds.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.getUTCSeconds.js
@@ -4,4 +4,5 @@ test("basic functionality", () => {
     expect(d.getUTCSeconds()).not.toBeNaN();
     expect(d.getUTCSeconds()).toBeGreaterThanOrEqual(0);
     expect(d.getUTCSeconds()).toBeLessThanOrEqual(59);
+    expect(new Date(NaN).getUTCSeconds()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setFullYear.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setFullYear.js
new file mode 100644
index 0000000000..a9a957b0db
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setFullYear.js
@@ -0,0 +1,112 @@
+test("no arguments", () => {
+    let date = new Date(2021, 0, 1);
+    date.setFullYear();
+    expect(date.getTime()).toBe(NaN);
+});
+
+test("NaN or undefined as only argument", () => {
+    let date = new Date(2021, 0, 1);
+    date.setFullYear(NaN);
+    expect(date.getTime()).toBe(NaN);
+
+    date = new Date(2021, 0, 1);
+    date.setFullYear(undefined);
+    expect(date.getTime()).toBe(NaN);
+
+    date = new Date(2021, 0, 1);
+    date.setFullYear("");
+    expect(date.getFullYear()).toBe(0);
+
+    date = new Date(2021, 0, 1);
+    date.setFullYear("a");
+    expect(date.getTime()).toBe(NaN);
+});
+
+test("Only year as argument", () => {
+    let date = new Date(2021, 0, 1);
+
+    date.setFullYear(1992);
+    expect(date.getFullYear()).toBe(1992);
+    expect(date.getMonth()).toBe(0);
+    expect(date.getDate()).toBe(1);
+    expect(date.getHours()).toBe(0);
+    expect(date.getMinutes()).toBe(0);
+    expect(date.getSeconds()).toBe(0);
+    expect(date.getMilliseconds()).toBe(0);
+});
+
+test("Year and month as arguments", () => {
+    let date = new Date(2021, 0, 1);
+
+    date.setFullYear(2021, 3);
+    expect(date.getFullYear()).toBe(2021);
+    expect(date.getMonth()).toBe(2);
+    expect(date.getDate()).toBe(1);
+    expect(date.getHours()).toBe(0);
+    expect(date.getMinutes()).toBe(0);
+    expect(date.getSeconds()).toBe(0);
+    expect(date.getMilliseconds()).toBe(0);
+});
+
+test("Year, month, and day as arguments", () => {
+    let date = new Date(2021, 0, 1);
+
+    date.setFullYear(2021, 3, 16);
+    expect(date.getFullYear()).toBe(2021);
+    expect(date.getMonth()).toBe(2);
+    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("NaN or undefined in any arguments", () => {
+    let date = new Date(2021, 0, 1);
+    date.setFullYear(NaN, 3, 16);
+    expect(date.getTime()).toBe(NaN);
+
+    date = new Date(2021, 0, 1);
+    date.setFullYear(2021, NaN, 16);
+    expect(date.getTime()).toBe(NaN);
+
+    date = new Date(2021, 0, 1);
+    date.setFullYear(2021, 3, NaN);
+    expect(date.getTime()).toBe(NaN);
+
+    date = new Date(2021, 0, 1);
+    date.setFullYear(undefined, 3, 16);
+    expect(date.getTime()).toBe(NaN);
+
+    date = new Date(2021, 0, 1);
+    date.setFullYear(2021, undefined, 16);
+    expect(date.getTime()).toBe(NaN);
+
+    date = new Date(2021, 0, 1);
+    date.setFullYear(2021, 3, undefined);
+    expect(date.getTime()).toBe(NaN);
+
+    date.setFullYear(2021, 3, 16);
+    expect(date.getFullYear()).toBe(2021);
+    expect(date.getMonth()).toBe(2);
+    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.setFullYear(NaN, 3, 16);
+    expect(date.getTime()).toBe(NaN);
+
+    date.setFullYear(2021, 3, 16);
+    expect(date.getFullYear()).toBe(2021);
+    expect(date.getMonth()).toBe(2);
+    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.setHours.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setHours.js
index f85477aa23..78cee7e1cf 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setHours.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setHours.js
@@ -18,4 +18,10 @@ test("basic functionality", () => {
     expect(d.getMinutes()).toBe(30);
     expect(d.getSeconds()).toBe(50);
     expect(d.getMilliseconds()).toBe(600);
+
+    d.setHours("");
+    expect(d.getHours()).toBe(0);
+
+    d.setHours("a");
+    expect(d.getHours()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMilliseconds.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMilliseconds.js
index a750a35012..67b71cfcc7 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMilliseconds.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMilliseconds.js
@@ -3,4 +3,10 @@ test("basic functionality", () => {
 
     d.setMilliseconds(600);
     expect(d.getMilliseconds()).toBe(600);
+
+    d.setMilliseconds("");
+    expect(d.getMilliseconds()).toBe(0);
+
+    d.setMilliseconds("a");
+    expect(d.getMilliseconds()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMinutes.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMinutes.js
index 2c7232cbf9..d5243ecd08 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMinutes.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMinutes.js
@@ -12,4 +12,10 @@ test("basic functionality", () => {
     expect(d.getMinutes()).toBe(30);
     expect(d.getSeconds()).toBe(50);
     expect(d.getMilliseconds()).toBe(600);
+
+    d.setMinutes("");
+    expect(d.getMinutes()).toBe(0);
+
+    d.setMinutes("a");
+    expect(d.getMinutes()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setSeconds.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setSeconds.js
index 4fa5d39c30..06f7521a1e 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setSeconds.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setSeconds.js
@@ -7,4 +7,10 @@ test("basic functionality", () => {
     d.setSeconds(50, 600);
     expect(d.getSeconds()).toBe(50);
     expect(d.getMilliseconds()).toBe(600);
+
+    d.setSeconds("");
+    expect(d.getSeconds()).toBe(0);
+
+    d.setSeconds("a");
+    expect(d.getSeconds()).toBe(NaN);
 });
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toISOString.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toISOString.js
index 2b380fc24d..eae4622796 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toISOString.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toISOString.js
@@ -4,4 +4,8 @@ test("basic functionality", () => {
     expect(new Date(Date.UTC(1950)).toISOString()).toBe("1950-01-01T00:00:00.000Z");
     expect(new Date(Date.UTC(1800)).toISOString()).toBe("1800-01-01T00:00:00.000Z");
     expect(new Date(Date.UTC(-100)).toISOString()).toBe("-000100-01-01T00:00:00.000Z");
+
+    expect(() => {
+        new Date(NaN).toISOString();
+    }).toThrowWithMessage(RangeError, "Invalid time value");
 });