LibJS: Implement Temporal.Instant.fromEpochMilliseconds()

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/66ff7722543
Pull-request: https://github.com/SerenityOS/serenity/pull/8580

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -143,6 +143,7 @@ namespace JS {
     P(fromCharCode)                          \
     P(fromCodePoint)                         \
     P(fromEntries)                           \
+    P(fromEpochMilliseconds)                 \
     P(fromEpochSeconds)                      \
     P(fround)                                \
     P(gc)                                    \

Userland/Libraries/LibJS/Runtime/Temporal/InstantConstructor.cpp

@@ -28,6 +28,7 @@ void InstantConstructor::initialize(GlobalObject& global_object)
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.fromEpochSeconds, from_epoch_seconds, 1, attr);
+    define_native_function(vm.names.fromEpochMilliseconds, from_epoch_milliseconds, 1, attr);
 
     define_direct_property(vm.names.length, Value(1), Attribute::Configurable);
 }
@@ -90,4 +91,30 @@ JS_DEFINE_NATIVE_FUNCTION(InstantConstructor::from_epoch_seconds)
     return create_temporal_instant(global_object, *epoch_nanoseconds);
 }
 
+// 8.2.4 Temporal.Instant.fromEpochMilliseconds ( epochMilliseconds ), https://tc39.es/proposal-temporal/#sec-temporal.instant.fromepochmilliseconds
+JS_DEFINE_NATIVE_FUNCTION(InstantConstructor::from_epoch_milliseconds)
+{
+    // 1. Set epochMilliseconds to ? ToNumber(epochMilliseconds).
+    auto epoch_milliseconds_value = vm.argument(0).to_number(global_object);
+    if (vm.exception())
+        return {};
+
+    // 2. Set epochMilliseconds to ? NumberToBigInt(epochMilliseconds).
+    auto* epoch_milliseconds = number_to_bigint(global_object, epoch_milliseconds_value);
+    if (vm.exception())
+        return {};
+
+    // 3. Let epochNanoseconds be epochMilliseconds × 10^6ℤ.
+    auto* epoch_nanoseconds = js_bigint(vm.heap(), epoch_milliseconds->big_integer().multiplied_by(Crypto::UnsignedBigInteger { 1'000'000 }));
+
+    // 4. If ! IsValidEpochNanoseconds(epochNanoseconds) is false, throw a RangeError exception.
+    if (!is_valid_epoch_nanoseconds(*epoch_nanoseconds)) {
+        vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidEpochNanoseconds);
+        return {};
+    }
+
+    // 5. Return ? CreateTemporalInstant(epochNanoseconds).
+    return create_temporal_instant(global_object, *epoch_nanoseconds);
+}
+
 }

Userland/Libraries/LibJS/Runtime/Temporal/InstantConstructor.h

@@ -25,6 +25,7 @@ private:
     virtual bool has_constructor() const override { return true; }
 
     JS_DECLARE_NATIVE_FUNCTION(from_epoch_seconds);
+    JS_DECLARE_NATIVE_FUNCTION(from_epoch_milliseconds);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/Temporal/Instant/Instant.fromEpochMilliseconds.js

@@ -0,0 +1,52 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.Instant.fromEpochMilliseconds).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        expect(Temporal.Instant.fromEpochMilliseconds(0).epochMilliseconds).toBe(0);
+        expect(Temporal.Instant.fromEpochMilliseconds(1).epochMilliseconds).toBe(1);
+        expect(Temporal.Instant.fromEpochMilliseconds(999_999_999).epochMilliseconds).toBe(
+            999_999_999
+        );
+        expect(
+            Temporal.Instant.fromEpochMilliseconds(8_640_000_000_000_000).epochMilliseconds
+        ).toBe(8_640_000_000_000_000);
+
+        expect(Temporal.Instant.fromEpochMilliseconds(-0).epochMilliseconds).toBe(0);
+        expect(Temporal.Instant.fromEpochMilliseconds(-1).epochMilliseconds).toBe(-1);
+        expect(Temporal.Instant.fromEpochMilliseconds(-999_999_999).epochMilliseconds).toBe(
+            -999_999_999
+        );
+        expect(
+            Temporal.Instant.fromEpochMilliseconds(-8_640_000_000_000_000).epochMilliseconds
+        ).toBe(-8_640_000_000_000_000);
+    });
+});
+
+test("errors", () => {
+    test("argument must be coercible to BigInt", () => {
+        expect(() => {
+            Temporal.Instant.fromEpochMilliseconds(1.23);
+        }).toThrowWithMessage(RangeError, "Cannot convert non-integral number to BigInt");
+        // NOTE: ToNumber is called on the argument first, so this is effectively NaN.
+        expect(() => {
+            Temporal.Instant.fromEpochMilliseconds("foo");
+        }).toThrowWithMessage(RangeError, "Cannot convert non-integral number to BigInt");
+    });
+
+    test("out-of-range epoch milliseconds value", () => {
+        expect(() => {
+            Temporal.Instant.fromEpochMilliseconds(8_640_000_000_000_001);
+        }).toThrowWithMessage(
+            RangeError,
+            "Invalid epoch nanoseconds value, must be in range -86400 * 10^17 to 86400 * 10^17"
+        );
+        expect(() => {
+            Temporal.Instant.fromEpochMilliseconds(-8_640_000_000_000_001);
+        }).toThrowWithMessage(
+            RangeError,
+            "Invalid epoch nanoseconds value, must be in range -86400 * 10^17 to 86400 * 10^17"
+        );
+    });
+});