LibJS: Implement Number.prototype.valueOf()

Userland/Libraries/LibJS/Runtime/ErrorTypes.h

@@ -53,7 +53,7 @@
     M(NotASymbol, "{} is not a symbol")                                                                                                 \
     M(NotIterable, "{} is not iterable")                                                                                                \
     M(NonExtensibleDefine, "Cannot define property {} on non-extensible object")                                                        \
-    M(NumberIncompatibleThis, "Number.prototype.{} method called with incompatible this target")                                        \
+    M(NumberIncompatibleThis, "Number.prototype.{}() called with incompatible this target")                                             \
     M(ObjectDefinePropertyReturnedFalse, "Object's [[DefineProperty]] method returned false")                                           \
     M(ObjectFreezeFailed, "Could not freeze object")                                                                                    \
     M(ObjectSealFailed, "Could not seal object")                                                                                        \

Userland/Libraries/LibJS/Runtime/NumberPrototype.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -32,26 +33,33 @@ void NumberPrototype::initialize(GlobalObject& object)
 {
     auto& vm = this->vm();
     Object::initialize(object);
-    define_native_function(vm.names.toString, to_string, 1, Attribute::Configurable | Attribute::Writable);
+    u8 attr = Attribute::Configurable | Attribute::Writable;
+    define_native_function(vm.names.toString, to_string, 1, attr);
+    define_native_function(vm.names.valueOf, value_of, 0, attr);
 }
 
 NumberPrototype::~NumberPrototype()
 {
 }
 
+// https://tc39.es/ecma262/#thisnumbervalue
+static Value this_number_value(GlobalObject& global_object, StringView const& name)
+{
+    auto& vm = global_object.vm();
+    auto this_value = vm.this_value(global_object);
+    if (this_value.is_number())
+        return this_value;
+    if (this_value.is_object() && is<NumberObject>(this_value.as_object()))
+        return static_cast<NumberObject&>(this_value.as_object()).value_of();
+    vm.throw_exception<TypeError>(global_object, ErrorType::NumberIncompatibleThis, name);
+    return {};
+}
+
 JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_string)
 {
-    Value number_value;
-
-    auto this_value = vm.this_value(global_object);
-    if (this_value.is_number()) {
-        number_value = this_value;
-    } else if (this_value.is_object() && is<NumberObject>(this_value.as_object())) {
-        number_value = static_cast<NumberObject&>(this_value.as_object()).value_of();
-    } else {
-        vm.throw_exception<TypeError>(global_object, ErrorType::NumberIncompatibleThis, "toString");
+    auto number_value = this_number_value(global_object, "toString");
+    if (vm.exception())
         return {};
-    }
 
     int radix;
     auto argument = vm.argument(0);
@@ -123,4 +131,9 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_string)
     return js_string(vm, String(characters.data(), characters.size()));
 }
 
+JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::value_of)
+{
+    return this_number_value(global_object, "valueOf");
+}
+
 }

Userland/Libraries/LibJS/Runtime/NumberPrototype.h

@@ -19,6 +19,7 @@ public:
     virtual ~NumberPrototype() override;
 
     JS_DECLARE_NATIVE_FUNCTION(to_string);
+    JS_DECLARE_NATIVE_FUNCTION(value_of);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/Number/Number.prototype.toString.js

@@ -75,7 +75,10 @@ describe("correct behavior", () => {
 test("errors", () => {
     test("must be called with numeric |this|", () => {
         [true, [], {}, Symbol("foo"), "bar", 1n].forEach(value => {
-            expect(() => Number.prototype.toString.call(value)).toThrow(TypeError);
+            expect(() => Number.prototype.toString.call(value)).toThrowWithMessage(
+                TypeError,
+                "Number.prototype.toString() called with incompatible this target"
+            );
         });
     });
 

Userland/Libraries/LibJS/Tests/builtins/Number/Number.prototype.valueOf.js

@@ -0,0 +1,21 @@
+describe("correct behavior", () => {
+    test("length", () => {
+        expect(Number.prototype.valueOf).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        expect(new Number(42).valueOf()).toBe(42);
+        expect(Number.prototype.valueOf.call(42)).toBe(42);
+    });
+});
+
+test("errors", () => {
+    test("must be called with numeric |this|", () => {
+        [true, [], {}, Symbol("foo"), "bar", 1n].forEach(value => {
+            expect(() => Number.prototype.valueOf.call(value)).toThrowWithMessage(
+                TypeError,
+                "Number.prototype.valueOf() called with incompatible this target"
+            );
+        });
+    });
+});