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LibJS: Implement Function.prototype.bind() according to the spec :^)
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4 changed files with 66 additions and 20 deletions
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@ -11,23 +11,37 @@
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namespace JS {
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BoundFunction::BoundFunction(GlobalObject& global_object, FunctionObject& bound_target_function, Value bound_this, Vector<Value> bound_arguments, i32 length)
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: FunctionObject(*global_object.function_prototype())
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// 10.4.1.3 BoundFunctionCreate ( targetFunction, boundThis, boundArgs ), https://tc39.es/ecma262/multipage/ordinary-and-exotic-objects-behaviours.html#sec-boundfunctioncreate
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ThrowCompletionOr<BoundFunction*> BoundFunction::create(GlobalObject& global_object, FunctionObject& target_function, Value bound_this, Vector<Value> bound_arguments)
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{
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// 1. Let proto be ? targetFunction.[[GetPrototypeOf]]().
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auto* prototype = TRY(target_function.internal_get_prototype_of());
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// 2. Let internalSlotsList be the list-concatenation of « [[Prototype]], [[Extensible]] » and the internal slots listed in Table 33.
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// 3. Let obj be ! MakeBasicObject(internalSlotsList).
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// 4. Set obj.[[Prototype]] to proto.
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// 5. Set obj.[[Call]] as described in 10.4.1.1.
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// 6. If IsConstructor(targetFunction) is true, then
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// a. Set obj.[[Construct]] as described in 10.4.1.2.
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// 7. Set obj.[[BoundTargetFunction]] to targetFunction.
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// 8. Set obj.[[BoundThis]] to boundThis.
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// 9. Set obj.[[BoundArguments]] to boundArgs.
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auto* object = global_object.heap().allocate<BoundFunction>(global_object, global_object, target_function, bound_this, move(bound_arguments), prototype);
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// 10. Return obj.
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return object;
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}
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BoundFunction::BoundFunction(GlobalObject& global_object, FunctionObject& bound_target_function, Value bound_this, Vector<Value> bound_arguments, Object* prototype)
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: FunctionObject(global_object, prototype)
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, m_bound_target_function(&bound_target_function)
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, m_bound_this(bound_this)
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, m_bound_arguments(move(bound_arguments))
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// FIXME: Non-standard and redundant, remove.
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, m_name(String::formatted("bound {}", bound_target_function.name()))
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, m_length(length)
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{
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}
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void BoundFunction::initialize(GlobalObject& global_object)
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{
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auto& vm = this->vm();
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Base::initialize(global_object);
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define_direct_property(vm.names.length, Value(m_length), Attribute::Configurable);
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}
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BoundFunction::~BoundFunction()
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{
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}
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@ -6,6 +6,7 @@
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#pragma once
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#include <LibJS/Runtime/Completion.h>
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#include <LibJS/Runtime/FunctionObject.h>
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namespace JS {
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@ -14,8 +15,9 @@ class BoundFunction final : public FunctionObject {
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JS_OBJECT(BoundFunction, FunctionObject);
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public:
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BoundFunction(GlobalObject&, FunctionObject& target_function, Value bound_this, Vector<Value> bound_arguments, i32 length);
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virtual void initialize(GlobalObject&) override;
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static ThrowCompletionOr<BoundFunction*> create(GlobalObject&, FunctionObject& target_function, Value bound_this, Vector<Value> bound_arguments);
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BoundFunction(GlobalObject&, FunctionObject& target_function, Value bound_this, Vector<Value> bound_arguments, Object* prototype);
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virtual ~BoundFunction();
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virtual ThrowCompletionOr<Value> internal_call(Value this_argument, MarkedVector<Value> arguments_list) override;
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@ -37,7 +39,6 @@ private:
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Vector<Value> m_bound_arguments; // [[BoundArguments]]
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FlyString m_name;
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i32 m_length { 0 };
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};
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}
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@ -16,6 +16,7 @@
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#include <LibJS/Runtime/FunctionPrototype.h>
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#include <LibJS/Runtime/GlobalObject.h>
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#include <LibJS/Runtime/NativeFunction.h>
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#include <LibJS/Runtime/ShadowRealm.h>
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namespace JS {
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@ -58,13 +59,19 @@ JS_DEFINE_NATIVE_FUNCTION(FunctionPrototype::apply)
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}
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// 20.2.3.2 Function.prototype.bind ( thisArg, ...args ), https://tc39.es/ecma262/#sec-function.prototype.bind
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// 3.1.2.1 Function.prototype.bind ( thisArg, ...args ), https://tc39.es/proposal-shadowrealm/#sec-function.prototype.bind
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JS_DEFINE_NATIVE_FUNCTION(FunctionPrototype::bind)
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{
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auto* this_object = TRY(vm.this_value(global_object).to_object(global_object));
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if (!this_object->is_function())
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return vm.throw_completion<TypeError>(global_object, ErrorType::NotAnObjectOfType, "Function");
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auto& this_function = static_cast<FunctionObject&>(*this_object);
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auto bound_this_arg = vm.argument(0);
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auto this_argument = vm.argument(0);
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// 1. Let Target be the this value.
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auto target_value = vm.this_value(global_object);
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// 2. If IsCallable(Target) is false, throw a TypeError exception.
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if (!target_value.is_function())
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return vm.throw_completion<TypeError>(global_object, ErrorType::NotAFunction, target_value.to_string_without_side_effects());
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auto& target = static_cast<FunctionObject&>(target_value.as_object());
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Vector<Value> arguments;
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if (vm.argument_count() > 1) {
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@ -72,7 +79,17 @@ JS_DEFINE_NATIVE_FUNCTION(FunctionPrototype::bind)
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arguments.remove(0);
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}
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return TRY(this_function.bind(bound_this_arg, move(arguments)));
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// 3. Let F be ? BoundFunctionCreate(Target, thisArg, args).
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auto* function = TRY(BoundFunction::create(global_object, target, this_argument, move(arguments)));
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// 4. Let argCount be the number of elements in args.
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auto arg_count = vm.argument_count() - 1;
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// 5. Perform ? CopyNameAndLength(F, Target, "bound", argCount).
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TRY(copy_name_and_length(global_object, *function, target, "bound"sv, arg_count));
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// 6. Return F.
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return function;
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}
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// 20.2.3.3 Function.prototype.call ( thisArg, ...args ), https://tc39.es/ecma262/#sec-function.prototype.call
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@ -33,6 +33,20 @@ describe("basic behavior", () => {
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)
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).toBe(12);
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});
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test("name has 'bound' prefix", () => {
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function foo() {}
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const boundFoo = foo.bind(123);
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expect(foo.name).toBe("foo");
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expect(boundFoo.name).toBe("bound foo");
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});
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test("prototype is inherited from target function", () => {
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function foo() {}
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Object.setPrototypeOf(foo, Array.prototype);
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const boundFoo = Function.prototype.bind.call(foo, 123);
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expect(Object.getPrototypeOf(boundFoo)).toBe(Array.prototype);
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});
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});
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describe("bound function arguments", () => {
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@ -144,6 +158,6 @@ describe("errors", () => {
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test("does not accept non-function values", () => {
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expect(() => {
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Function.prototype.bind.call("foo");
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}).toThrowWithMessage(TypeError, "Not an object of type Function");
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}).toThrowWithMessage(TypeError, "foo is not a function");
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});
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});
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