LibJS: Implement Function.prototype.bind()

Author: https://github.com/jack-karamanian
Commit: https://github.com/SerenityOS/serenity/commit/1fa0c7304d1
Pull-request: https://github.com/SerenityOS/serenity/pull/1863
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/linusg

Libraries/LibJS/AST.cpp

@@ -114,9 +114,8 @@ Value CallExpression::execute(Interpreter& interpreter) const
     auto& function = static_cast<Function&>(callee.as_object());
 
     MarkedValueList arguments(interpreter.heap());
-    for (auto bound_argument : function.bound_arguments()) {
-        arguments.append(bound_argument);
-    }
+    arguments.values().append(function.bound_arguments());
+
     for (size_t i = 0; i < m_arguments.size(); ++i) {
         auto value = m_arguments[i].execute(interpreter);
         if (interpreter.exception())

Libraries/LibJS/Forward.h

@@ -52,6 +52,7 @@
 namespace JS {
 
 class ASTNode;
+class BoundFunction;
 class Cell;
 class DeferGC;
 class Error;

Libraries/LibJS/Makefile

@@ -12,6 +12,7 @@ OBJS = \
     Runtime/BooleanConstructor.o \
     Runtime/BooleanObject.o \
     Runtime/BooleanPrototype.o \
+    Runtime/BoundFunction.o \
     Runtime/Cell.o \
     Runtime/ConsoleObject.o \
     Runtime/Date.o \

Libraries/LibJS/Runtime/BoundFunction.cpp

@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2020, Jack Karamanian <karamanian.jack@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <LibJS/Interpreter.h>
+#include <LibJS/Runtime/BoundFunction.h>
+#include <LibJS/Runtime/GlobalObject.h>
+
+namespace JS {
+
+BoundFunction::BoundFunction(Function& target_function, Value bound_this, Vector<Value> arguments, i32 length, Object* constructor_prototype)
+    : Function::Function(*interpreter().global_object().function_prototype(), bound_this, move(arguments))
+    , m_target_function(&target_function)
+    , m_constructor_prototype(constructor_prototype)
+    , m_name(String::format("bound %s", target_function.name().characters()))
+{
+    put("length", Value(length));
+}
+
+BoundFunction::~BoundFunction()
+{
+}
+
+Value BoundFunction::call(Interpreter& interpreter)
+{
+    return m_target_function->call(interpreter);
+}
+
+Value BoundFunction::construct(Interpreter& interpreter)
+{
+    if (auto this_value = interpreter.this_value(); m_constructor_prototype && this_value.is_object()) {
+        this_value.as_object().set_prototype(m_constructor_prototype);
+    }
+    return m_target_function->construct(interpreter);
+}
+
+LexicalEnvironment* BoundFunction::create_environment()
+{
+    return m_target_function->create_environment();
+}
+
+void BoundFunction::visit_children(Visitor& visitor)
+{
+    Function::visit_children(visitor);
+    visitor.visit(m_target_function);
+    visitor.visit(m_constructor_prototype);
+}
+
+}

Libraries/LibJS/Runtime/BoundFunction.h

@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2020, Jack Karamanian <karamanian.jack@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <LibJS/Runtime/Function.h>
+
+namespace JS {
+
+class BoundFunction final : public Function {
+public:
+    BoundFunction(Function& target_function, Value bound_this, Vector<Value> arguments, i32 length, Object* constructor_prototype);
+
+    virtual ~BoundFunction();
+
+    virtual Value call(Interpreter& interpreter) override;
+
+    virtual Value construct(Interpreter& interpreter) override;
+
+    virtual LexicalEnvironment* create_environment() override;
+
+    virtual void visit_children(Visitor&) override;
+
+    virtual const FlyString& name() const override
+    {
+        return m_name;
+    }
+
+    Function& target_function() const
+    {
+        return *m_target_function;
+    }
+
+private:
+    virtual bool is_bound_function() const override { return true; }
+    virtual const char* class_name() const override { return "BoundFunction"; }
+
+    Function* m_target_function = nullptr;
+    Object* m_constructor_prototype = nullptr;
+    FlyString m_name;
+};
+
+}

Libraries/LibJS/Runtime/Function.cpp

@@ -25,7 +25,9 @@
  */
 
 #include <LibJS/Interpreter.h>
+#include <LibJS/Runtime/BoundFunction.h>
 #include <LibJS/Runtime/Function.h>
+#include <LibJS/Runtime/GlobalObject.h>
 
 namespace JS {
 
@@ -41,6 +43,50 @@ Function::Function(Object& prototype, Optional<Value> bound_this, Vector<Value>
 {
 }
 
+BoundFunction* Function::bind(Value bound_this_value, Vector<Value> arguments)
+{
+
+    Function& target_function = is_bound_function() ? static_cast<BoundFunction&>(*this).target_function() : *this;
+
+    auto bound_this_object
+        = [bound_this_value, this]() -> Value {
+        if (bound_this().has_value()) {
+            return bound_this().value();
+        }
+        switch (bound_this_value.type()) {
+        case Value::Type::Undefined:
+        case Value::Type::Null:
+            // FIXME: Null or undefined should be passed through in strict mode.
+            return &interpreter().global_object();
+        default:
+            return bound_this_value.to_object(interpreter().heap());
+        }
+    }();
+
+    i32 computed_length = 0;
+    auto length_property = get("length");
+    if (interpreter().exception()) {
+        return nullptr;
+    }
+    if (length_property.has_value() && length_property.value().is_number()) {
+        computed_length = max(0, length_property.value().to_i32() - static_cast<i32>(arguments.size()));
+    }
+
+    Object* constructor_prototype = nullptr;
+    auto prototype_property = target_function.get("prototype");
+    if (interpreter().exception()) {
+        return nullptr;
+    }
+    if (prototype_property.has_value() && prototype_property.value().is_object()) {
+        constructor_prototype = &prototype_property.value().as_object();
+    }
+
+    auto all_bound_arguments = bound_arguments();
+    all_bound_arguments.append(move(arguments));
+
+    return interpreter().heap().allocate<BoundFunction>(target_function, bound_this_object, move(all_bound_arguments), computed_length, constructor_prototype);
+}
+
 void Function::visit_children(Visitor& visitor)
 {
     Object::visit_children(visitor);

Libraries/LibJS/Runtime/Function.h

@@ -42,6 +42,8 @@ public:
 
     virtual void visit_children(Visitor&) override;
 
+    BoundFunction* bind(Value bound_this_value, Vector<Value> arguments);
+
     Optional<Value> bound_this() const
     {
         return m_bound_this;

Libraries/LibJS/Runtime/FunctionPrototype.cpp

@@ -28,6 +28,7 @@
 #include <AK/StringBuilder.h>
 #include <LibJS/AST.h>
 #include <LibJS/Interpreter.h>
+#include <LibJS/Runtime/BoundFunction.h>
 #include <LibJS/Runtime/Error.h>
 #include <LibJS/Runtime/Function.h>
 #include <LibJS/Runtime/FunctionPrototype.h>
@@ -84,8 +85,19 @@ Value FunctionPrototype::bind(Interpreter& interpreter)
     auto* this_object = interpreter.this_value().to_object(interpreter.heap());
     if (!this_object)
         return {};
-    // FIXME: Implement me :^)
-    ASSERT_NOT_REACHED();
+    if (!this_object->is_function())
+        return interpreter.throw_exception<TypeError>("Not a Function object");
+
+    auto& this_function = static_cast<Function&>(*this_object);
+    auto bound_this_arg = interpreter.argument(0);
+
+    Vector<Value> arguments;
+    if (interpreter.argument_count() > 1) {
+        arguments = interpreter.call_frame().arguments;
+        arguments.remove(0);
+    }
+
+    return this_function.bind(bound_this_arg, move(arguments));
 }
 
 Value FunctionPrototype::call(Interpreter& interpreter)
@@ -117,7 +129,7 @@ Value FunctionPrototype::to_string(Interpreter& interpreter)
     String function_parameters = "";
     String function_body;
 
-    if (this_object->is_native_function()) {
+    if (this_object->is_native_function() || this_object->is_bound_function()) {
         function_body = String::format("  [%s]", this_object->class_name());
     } else {
         auto& parameters = static_cast<ScriptFunction*>(this_object)->parameters();

Libraries/LibJS/Runtime/Object.h

@@ -72,6 +72,7 @@ public:
     virtual bool is_error() const { return false; }
     virtual bool is_function() const { return false; }
     virtual bool is_native_function() const { return false; }
+    virtual bool is_bound_function() const { return false; }
     virtual bool is_native_property() const { return false; }
     virtual bool is_string_object() const { return false; }
 

Libraries/LibJS/Tests/Function.prototype.bind.js

@@ -0,0 +1,112 @@
+load("test-common.js");
+
+try {
+    assert(Function.prototype.bind.length === 1);
+
+    var charAt = String.prototype.charAt.bind("bar");
+    assert(charAt(0) + charAt(1) + charAt(2) === "bar");
+
+    function getB() {
+        return this.toUpperCase().charAt(0);
+    }
+    assert(getB.bind("bar")() === "B");
+
+    function sum(a, b, c) {
+        return a + b + c;
+    }
+
+    // Arguments should be able to be bound to a function.
+    var boundSum = sum.bind(null, 10, 5);
+    assert(isNaN(boundSum()));
+
+    assert(boundSum(5) === 20);
+    assert(boundSum(5, 6, 7) === 20);
+
+    // Arguments should be appended to a BoundFunction's bound arguments.
+    assert(boundSum.bind(null, 5)() === 20);
+
+    // A BoundFunction's length property should be adjusted based on the number
+    // of bound arguments.
+    assert(sum.length === 3);
+    assert(boundSum.length === 1);
+    assert(boundSum.bind(null, 5).length === 0);
+    assert(boundSum.bind(null, 5, 6, 7, 8).length === 0);
+
+    function identity() {
+        return this;
+    }
+
+    // It should capture the global object if the |this| value is null or undefined.
+    assert(identity.bind()() === globalThis);
+    assert(identity.bind(null)() === globalThis);
+    assert(identity.bind(undefined)() === globalThis);
+
+    function Foo() {
+        assert(identity.bind()() === globalThis);
+        assert(identity.bind(this)() === this);
+    }
+    new Foo();
+
+    // Primitive |this| values should be converted to objects.
+    assert(identity.bind("foo")() instanceof String);
+    assert(identity.bind(123)() instanceof Number);
+    assert(identity.bind(true)() instanceof Boolean);
+
+    // It should retain |this| values passed to it.
+    var obj = { foo: "bar" };
+
+    assert(identity.bind(obj)() === obj);
+
+    // The bound |this| can not be changed once set
+    assert(identity.bind("foo").bind(123)() instanceof String);
+
+    // The bound |this| value should have no effect on a constructor.
+    function Bar() {
+        this.x = 3;
+        this.y = 4;
+    }
+    Bar.prototype.baz = "baz";
+
+    var BoundBar = Bar.bind({ u: 5, v: 6 });
+
+    var bar = new BoundBar();
+    assert(bar.x === 3);
+    assert(bar.y === 4);
+    assert(typeof bar.u === "undefined");
+    assert(typeof bar.v === "undefined");
+    // Objects constructed from BoundFunctions should retain the prototype of the original function.
+    assert(bar.baz === "baz");
+    // BoundFunctions should not have a prototype property.
+    assert(typeof BoundBar.prototype === "undefined");
+
+    // Function.prototype.bind should not accept non-function values.
+    assertThrowsError(() => {
+        Function.prototype.bind.call("foo");
+    }, {
+        error: TypeError,
+        message: "Not a Function object"
+    });
+
+    // A constructor's arguments should be able to be bound.
+    var Make5 = Number.bind(null, 5);
+    assert(Make5() === 5);
+    assert(new Make5().valueOf() === 5);
+
+    // FIXME: Uncomment me when strict mode is implemented
+    //     function strictIdentity() {
+    //         return this;
+    //     }
+
+    //     assert(strictIdentity.bind()() === undefined);
+    //     assert(strictIdentity.bind(null)() === null);
+    //     assert(strictIdentity.bind(undefined)() === undefined);
+    // })();
+
+    // FIXME: Uncomment me when arrow functions have the correct |this| value.
+    // // Arrow functions can not have their |this| value set.
+    // assert((() => this).bind("foo")() === globalThis)
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}