Implement closure functions (#1442)

boa/examples/closures.rs

@@ -0,0 +1,20 @@
+use boa::{Context, JsString, Value};
+
+fn main() -> Result<(), Value> {
+    let mut context = Context::new();
+
+    let variable = JsString::new("I am a captured variable");
+
+    // We register a global closure function that has the name 'closure' with length 0.
+    context.register_global_closure("closure", 0, move |_, _, _| {
+        // This value is captured from main function.
+        Ok(variable.clone().into())
+    })?;
+
+    assert_eq!(
+        context.eval("closure()")?,
+        "I am a captured variable".into()
+    );
+
+    Ok(())
+}

boa/src/builtins/array/mod.rs

@@ -45,16 +45,14 @@ impl BuiltIn for Array {
 
         let symbol_iterator = WellKnownSymbols::iterator();
 
-        let get_species = FunctionBuilder::new(context, Self::get_species)
+        let get_species = FunctionBuilder::native(context, Self::get_species)
             .name("get [Symbol.species]")
             .constructable(false)
-            .callable(true)
             .build();
 
-        let values_function = FunctionBuilder::new(context, Self::values)
+        let values_function = FunctionBuilder::native(context, Self::values)
             .name("values")
             .length(0)
-            .callable(true)
             .constructable(false)
             .build();
 
@@ -166,7 +164,7 @@ impl Array {
                 // i. Let intLen be ! ToUint32(len).
                 let int_len = len.to_u32(context).unwrap();
                 // ii. If SameValueZero(intLen, len) is false, throw a RangeError exception.
-                if !Value::same_value_zero(&int_len.into(), &len) {
+                if !Value::same_value_zero(&int_len.into(), len) {
                     return Err(context.construct_range_error("invalid array length"));
                 }
                 int_len

boa/src/builtins/function/mod.rs

@@ -15,7 +15,7 @@ use crate::object::PROTOTYPE;
 use crate::{
     builtins::{Array, BuiltIn},
     environment::lexical_environment::Environment,
-    gc::{empty_trace, Finalize, Trace},
+    gc::{custom_trace, empty_trace, Finalize, Trace},
     object::{ConstructorBuilder, FunctionBuilder, GcObject, Object, ObjectData},
     property::{Attribute, DataDescriptor},
     syntax::ast::node::{FormalParameter, RcStatementList},
@@ -23,13 +23,17 @@ use crate::{
 };
 use bitflags::bitflags;
 use std::fmt::{self, Debug};
+use std::rc::Rc;
 
 #[cfg(test)]
 mod tests;
 
-/// _fn(this, arguments, context) -> ResultValue_ - The signature of a built-in function
+/// _fn(this, arguments, context) -> ResultValue_ - The signature of a native built-in function
 pub type NativeFunction = fn(&Value, &[Value], &mut Context) -> Result<Value>;
 
+/// _fn(this, arguments, context) -> ResultValue_ - The signature of a closure built-in function
+pub type ClosureFunction = dyn Fn(&Value, &[Value], &mut Context) -> Result<Value>;
+
 #[derive(Clone, Copy, Finalize)]
 pub struct BuiltInFunction(pub(crate) NativeFunction);
 
@@ -52,31 +56,12 @@ impl Debug for BuiltInFunction {
 bitflags! {
     #[derive(Finalize, Default)]
     pub struct FunctionFlags: u8 {
-        const CALLABLE = 0b0000_0001;
         const CONSTRUCTABLE = 0b0000_0010;
         const LEXICAL_THIS_MODE = 0b0000_0100;
     }
 }
 
 impl FunctionFlags {
-    pub(crate) fn from_parameters(callable: bool, constructable: bool) -> Self {
-        let mut flags = Self::default();
-
-        if callable {
-            flags |= Self::CALLABLE;
-        }
-        if constructable {
-            flags |= Self::CONSTRUCTABLE;
-        }
-
-        flags
-    }
-
-    #[inline]
-    pub(crate) fn is_callable(&self) -> bool {
-        self.contains(Self::CALLABLE)
-    }
-
     #[inline]
     pub(crate) fn is_constructable(&self) -> bool {
         self.contains(Self::CONSTRUCTABLE)
@@ -97,9 +82,16 @@ unsafe impl Trace for FunctionFlags {
 /// FunctionBody is specific to this interpreter, it will either be Rust code or JavaScript code (AST Node)
 ///
 /// <https://tc39.es/ecma262/#sec-ecmascript-function-objects>
-#[derive(Debug, Clone, Finalize, Trace)]
+#[derive(Finalize)]
 pub enum Function {
-    BuiltIn(BuiltInFunction, FunctionFlags),
+    Native {
+        function: BuiltInFunction,
+        constructable: bool,
+    },
+    Closure {
+        function: Rc<ClosureFunction>,
+        constructable: bool,
+    },
     Ordinary {
         flags: FunctionFlags,
         body: RcStatementList,
@@ -108,6 +100,24 @@ pub enum Function {
     },
 }
 
+impl Debug for Function {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Function {{ ... }}")
+    }
+}
+
+unsafe impl Trace for Function {
+    custom_trace!(this, {
+        match this {
+            Function::Native { .. } => {}
+            Function::Closure { .. } => {}
+            Function::Ordinary { environment, .. } => {
+                mark(environment);
+            }
+        }
+    });
+}
+
 impl Function {
     // Adds the final rest parameters to the Environment as an array
     pub(crate) fn add_rest_param(
@@ -154,18 +164,11 @@ impl Function {
             .expect("Failed to intialize binding");
     }
 
-    /// Returns true if the function object is callable.
-    pub fn is_callable(&self) -> bool {
-        match self {
-            Self::BuiltIn(_, flags) => flags.is_callable(),
-            Self::Ordinary { flags, .. } => flags.is_callable(),
-        }
-    }
-
     /// Returns true if the function object is constructable.
     pub fn is_constructable(&self) -> bool {
         match self {
-            Self::BuiltIn(_, flags) => flags.is_constructable(),
+            Self::Native { constructable, .. } => *constructable,
+            Self::Closure { constructable, .. } => *constructable,
             Self::Ordinary { flags, .. } => flags.is_constructable(),
         }
     }
@@ -230,7 +233,10 @@ pub fn make_builtin_fn<N>(
     let _timer = BoaProfiler::global().start_event(&format!("make_builtin_fn: {}", &name), "init");
 
     let mut function = Object::function(
-        Function::BuiltIn(function.into(), FunctionFlags::CALLABLE),
+        Function::Native {
+            function: function.into(),
+            constructable: false,
+        },
         interpreter
             .standard_objects()
             .function_object()
@@ -270,10 +276,10 @@ impl BuiltInFunctionObject {
             .expect("this should be an object")
             .set_prototype_instance(prototype.into());
 
-        this.set_data(ObjectData::Function(Function::BuiltIn(
-            BuiltInFunction(|_, _, _| Ok(Value::undefined())),
-            FunctionFlags::CALLABLE | FunctionFlags::CONSTRUCTABLE,
-        )));
+        this.set_data(ObjectData::Function(Function::Native {
+            function: BuiltInFunction(|_, _, _| Ok(Value::undefined())),
+            constructable: true,
+        }));
         Ok(this)
     }
 
@@ -342,10 +348,9 @@ impl BuiltIn for BuiltInFunctionObject {
         let _timer = BoaProfiler::global().start_event("function", "init");
 
         let function_prototype = context.standard_objects().function_object().prototype();
-        FunctionBuilder::new(context, Self::prototype)
+        FunctionBuilder::native(context, Self::prototype)
             .name("")
             .length(0)
-            .callable(true)
             .constructable(false)
             .build_function_prototype(&function_prototype);
 

boa/src/builtins/map/mod.rs

@@ -46,16 +46,14 @@ impl BuiltIn for Map {
         let to_string_tag = WellKnownSymbols::to_string_tag();
         let iterator_symbol = WellKnownSymbols::iterator();
 
-        let get_species = FunctionBuilder::new(context, Self::get_species)
+        let get_species = FunctionBuilder::native(context, Self::get_species)
             .name("get [Symbol.species]")
             .constructable(false)
-            .callable(true)
             .build();
 
-        let entries_function = FunctionBuilder::new(context, Self::entries)
+        let entries_function = FunctionBuilder::native(context, Self::entries)
             .name("entries")
             .length(0)
-            .callable(true)
             .constructable(false)
             .build();
 

boa/src/builtins/object/mod.rs

@@ -360,7 +360,7 @@ impl Object {
     /// Define a property in an object
     pub fn define_property(_: &Value, args: &[Value], context: &mut Context) -> Result<Value> {
         let object = args.get(0).cloned().unwrap_or_else(Value::undefined);
-        if let Some(mut object) = object.as_object() {
+        if let Some(object) = object.as_object() {
             let key = args
                 .get(1)
                 .unwrap_or(&Value::undefined())

boa/src/builtins/regexp/mod.rs

@@ -75,53 +75,44 @@ impl BuiltIn for RegExp {
     fn init(context: &mut Context) -> (&'static str, Value, Attribute) {
         let _timer = BoaProfiler::global().start_event(Self::NAME, "init");
 
-        let get_species = FunctionBuilder::new(context, Self::get_species)
+        let get_species = FunctionBuilder::native(context, Self::get_species)
             .name("get [Symbol.species]")
             .constructable(false)
-            .callable(true)
             .build();
 
         let flag_attributes = Attribute::CONFIGURABLE | Attribute::NON_ENUMERABLE;
 
-        let get_global = FunctionBuilder::new(context, Self::get_global)
+        let get_global = FunctionBuilder::native(context, Self::get_global)
             .name("get global")
             .constructable(false)
-            .callable(true)
             .build();
-        let get_ignore_case = FunctionBuilder::new(context, Self::get_ignore_case)
+        let get_ignore_case = FunctionBuilder::native(context, Self::get_ignore_case)
             .name("get ignoreCase")
             .constructable(false)
-            .callable(true)
             .build();
-        let get_multiline = FunctionBuilder::new(context, Self::get_multiline)
+        let get_multiline = FunctionBuilder::native(context, Self::get_multiline)
             .name("get multiline")
             .constructable(false)
-            .callable(true)
             .build();
-        let get_dot_all = FunctionBuilder::new(context, Self::get_dot_all)
+        let get_dot_all = FunctionBuilder::native(context, Self::get_dot_all)
             .name("get dotAll")
             .constructable(false)
-            .callable(true)
             .build();
-        let get_unicode = FunctionBuilder::new(context, Self::get_unicode)
+        let get_unicode = FunctionBuilder::native(context, Self::get_unicode)
             .name("get unicode")
             .constructable(false)
-            .callable(true)
             .build();
-        let get_sticky = FunctionBuilder::new(context, Self::get_sticky)
+        let get_sticky = FunctionBuilder::native(context, Self::get_sticky)
             .name("get sticky")
             .constructable(false)
-            .callable(true)
             .build();
-        let get_flags = FunctionBuilder::new(context, Self::get_flags)
+        let get_flags = FunctionBuilder::native(context, Self::get_flags)
             .name("get flags")
             .constructable(false)
-            .callable(true)
             .build();
-        let get_source = FunctionBuilder::new(context, Self::get_source)
+        let get_source = FunctionBuilder::native(context, Self::get_source)
             .name("get source")
             .constructable(false)
-            .callable(true)
             .build();
         let regexp_object = ConstructorBuilder::with_standard_object(
             context,

boa/src/builtins/set/mod.rs

@@ -39,14 +39,12 @@ impl BuiltIn for Set {
     fn init(context: &mut Context) -> (&'static str, Value, Attribute) {
         let _timer = BoaProfiler::global().start_event(Self::NAME, "init");
 
-        let get_species = FunctionBuilder::new(context, Self::get_species)
+        let get_species = FunctionBuilder::native(context, Self::get_species)
             .name("get [Symbol.species]")
             .constructable(false)
-            .callable(true)
             .build();
 
-        let size_getter = FunctionBuilder::new(context, Self::size_getter)
-            .callable(true)
+        let size_getter = FunctionBuilder::native(context, Self::size_getter)
             .constructable(false)
             .name("get size")
             .build();
@@ -55,10 +53,9 @@ impl BuiltIn for Set {
 
         let to_string_tag = WellKnownSymbols::to_string_tag();
 
-        let values_function = FunctionBuilder::new(context, Self::values)
+        let values_function = FunctionBuilder::native(context, Self::values)
             .name("values")
             .length(0)
-            .callable(true)
             .constructable(false)
             .build();
 

boa/src/builtins/symbol/mod.rs

@@ -97,10 +97,9 @@ impl BuiltIn for Symbol {
 
         let attribute = Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::PERMANENT;
 
-        let get_description = FunctionBuilder::new(context, Self::get_description)
+        let get_description = FunctionBuilder::native(context, Self::get_description)
             .name("get description")
             .constructable(false)
-            .callable(true)
             .build();
 
         let symbol_object = ConstructorBuilder::with_standard_object(

boa/src/context.rs

@@ -21,7 +21,7 @@ use crate::{
         },
         Parser,
     },
-    BoaProfiler, Executable, Result, Value,
+    BoaProfiler, Executable, JsString, Result, Value,
 };
 
 #[cfg(feature = "console")]
@@ -486,21 +486,24 @@ impl Context {
     }
 
     /// Utility to create a function Value for Function Declarations, Arrow Functions or Function Expressions
-    pub(crate) fn create_function<P, B>(
+    pub(crate) fn create_function<N, P, B>(
         &mut self,
+        name: N,
         params: P,
         body: B,
         flags: FunctionFlags,
     ) -> Result<Value>
     where
+        N: Into<JsString>,
         P: Into<Box<[FormalParameter]>>,
         B: Into<StatementList>,
     {
+        let name = name.into();
         let function_prototype: Value =
             self.standard_objects().function_object().prototype().into();
 
         // Every new function has a prototype property pre-made
-        let proto = Value::new_object(self);
+        let prototype = self.construct_object();
 
         let params = params.into();
         let params_len = params.len();
@@ -511,30 +514,48 @@ impl Context {
             environment: self.get_current_environment().clone(),
         };
 
-        let new_func = Object::function(func, function_prototype);
-
-        let val = Value::from(new_func);
+        let function = GcObject::new(Object::function(func, function_prototype));
 
         // Set constructor field to the newly created Value (function object)
-        proto.set_field("constructor", val.clone(), false, self)?;
+        let constructor = DataDescriptor::new(
+            function.clone(),
+            Attribute::WRITABLE | Attribute::NON_ENUMERABLE | Attribute::CONFIGURABLE,
+        );
+        prototype.define_property_or_throw("constructor", constructor, self)?;
 
-        val.set_field(PROTOTYPE, proto, false, self)?;
-        val.set_field("length", Value::from(params_len), false, self)?;
+        let prototype = DataDescriptor::new(
+            prototype,
+            Attribute::WRITABLE | Attribute::NON_ENUMERABLE | Attribute::PERMANENT,
+        );
+        function.define_property_or_throw(PROTOTYPE, prototype, self)?;
+        let length = DataDescriptor::new(
+            params_len,
+            Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::CONFIGURABLE,
+        );
+        function.define_property_or_throw("length", length, self)?;
+        let name = DataDescriptor::new(
+            name,
+            Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::CONFIGURABLE,
+        );
+        function.define_property_or_throw("name", name, self)?;
 
-        Ok(val)
+        Ok(function.into())
     }
 
-    /// Register a global function.
+    /// Register a global native function.
+    ///
+    /// This is more efficient that creating a closure function, since this does not allocate,
+    /// it is just a function pointer.
     ///
-    /// The function will be both `callable` and `constructable` (call with `new`).
+    /// The function will be both `constructable` (call with `new`).
     ///
     /// The function will be bound to the global object with `writable`, `non-enumerable`
     /// and `configurable` attributes. The same as when you create a function in JavaScript.
     ///
     /// # Note
     ///
-    /// If you want to make a function only `callable` or `constructable`, or wish to bind it differently
-    /// to the global object, you can create the function object with [`FunctionBuilder`](crate::object::FunctionBuilder).
+    /// If you want to make a function only `constructable`, or wish to bind it differently
+    /// to the global object, you can create the function object with [`FunctionBuilder`](crate::object::FunctionBuilder::native).
     /// And bind it to the global object with [`Context::register_global_property`](Context::register_global_property) method.
     #[inline]
     pub fn register_global_function(
@@ -543,10 +564,40 @@ impl Context {
         length: usize,
         body: NativeFunction,
     ) -> Result<()> {
-        let function = FunctionBuilder::new(self, body)
+        let function = FunctionBuilder::native(self, body)
+            .name(name)
+            .length(length)
+            .constructable(true)
+            .build();
+
+        self.global_object().insert_property(
+            name,
+            function,
+            Attribute::WRITABLE | Attribute::NON_ENUMERABLE | Attribute::CONFIGURABLE,
+        );
+        Ok(())
+    }
+
+    /// Register a global closure function.
+    ///
+    /// The function will be both `constructable` (call with `new`).
+    ///
+    /// The function will be bound to the global object with `writable`, `non-enumerable`
+    /// and `configurable` attributes. The same as when you create a function in JavaScript.
+    ///
+    /// # Note
+    ///
+    /// If you want to make a function only `constructable`, or wish to bind it differently
+    /// to the global object, you can create the function object with [`FunctionBuilder`](crate::object::FunctionBuilder::closure).
+    /// And bind it to the global object with [`Context::register_global_property`](Context::register_global_property) method.
+    #[inline]
+    pub fn register_global_closure<F>(&mut self, name: &str, length: usize, body: F) -> Result<()>
+    where
+        F: Fn(&Value, &[Value], &mut Context) -> Result<Value> + 'static,
+    {
+        let function = FunctionBuilder::closure(self, body)
             .name(name)
             .length(length)
-            .callable(true)
             .constructable(true)
             .build();
 

boa/src/object/gcobject.rs

@@ -5,7 +5,7 @@
 use super::{NativeObject, Object, PROTOTYPE};
 use crate::{
     builtins::function::{
-        create_unmapped_arguments_object, BuiltInFunction, Function, NativeFunction,
+        create_unmapped_arguments_object, ClosureFunction, Function, NativeFunction,
     },
     context::StandardConstructor,
     environment::{
@@ -26,6 +26,7 @@ use std::{
     collections::HashMap,
     error::Error,
     fmt::{self, Debug, Display},
+    rc::Rc,
     result::Result as StdResult,
 };
 
@@ -46,6 +47,7 @@ pub struct GcObject(Gc<GcCell<Object>>);
 enum FunctionBody {
     BuiltInFunction(NativeFunction),
     BuiltInConstructor(NativeFunction),
+    Closure(Rc<ClosureFunction>),
     Ordinary(RcStatementList),
 }
 
@@ -139,17 +141,19 @@ impl GcObject {
                     .display()
                     .to_string();
                 return context.throw_type_error(format!("{} is not a constructor", name));
-            } else if !construct && !function.is_callable() {
-                return context.throw_type_error("function object is not callable");
             } else {
                 match function {
-                    Function::BuiltIn(BuiltInFunction(function), flags) => {
-                        if flags.is_constructable() || construct {
-                            FunctionBody::BuiltInConstructor(*function)
+                    Function::Native {
+                        function,
+                        constructable,
+                    } => {
+                        if *constructable || construct {
+                            FunctionBody::BuiltInConstructor(function.0)
                         } else {
-                            FunctionBody::BuiltInFunction(*function)
+                            FunctionBody::BuiltInFunction(function.0)
                         }
                     }
+                    Function::Closure { function, .. } => FunctionBody::Closure(function.clone()),
                     Function::Ordinary {
                         body,
                         params,
@@ -298,6 +302,7 @@ impl GcObject {
                 function(&Value::undefined(), args, context)
             }
             FunctionBody::BuiltInFunction(function) => function(this_target, args, context),
+            FunctionBody::Closure(function) => (function)(this_target, args, context),
             FunctionBody::Ordinary(body) => {
                 let result = body.run(context);
                 let this = context.get_this_binding();

boa/src/object/internal_methods.rs

@@ -152,7 +152,7 @@ impl GcObject {
     /// [spec]: https://tc39.es/ecma262/#sec-definepropertyorthrow
     #[inline]
     pub fn define_property_or_throw<K, P>(
-        &mut self,
+        &self,
         key: K,
         desc: P,
         context: &mut Context,

boa/src/object/mod.rs

@@ -3,7 +3,7 @@
 use crate::{
     builtins::{
         array::array_iterator::ArrayIterator,
-        function::{BuiltInFunction, Function, FunctionFlags, NativeFunction},
+        function::{Function, NativeFunction},
         map::map_iterator::MapIterator,
         map::ordered_map::OrderedMap,
         regexp::regexp_string_iterator::RegExpStringIterator,
@@ -22,6 +22,7 @@ use std::{
     any::Any,
     fmt::{self, Debug, Display},
     ops::{Deref, DerefMut},
+    rc::Rc,
 };
 
 #[cfg(test)]
@@ -264,7 +265,7 @@ impl Object {
     /// [spec]: https://tc39.es/ecma262/#sec-iscallable
     #[inline]
     pub fn is_callable(&self) -> bool {
-        matches!(self.data, ObjectData::Function(ref f) if f.is_callable())
+        matches!(self.data, ObjectData::Function(_))
     }
 
     /// It determines if Object is a function object with a `[[Construct]]` internal method.
@@ -682,24 +683,40 @@ where
 #[derive(Debug)]
 pub struct FunctionBuilder<'context> {
     context: &'context mut Context,
-    function: BuiltInFunction,
-    name: Option<String>,
+    function: Option<Function>,
+    name: JsString,
     length: usize,
-    callable: bool,
-    constructable: bool,
 }
 
 impl<'context> FunctionBuilder<'context> {
-    /// Create a new `FunctionBuilder`
+    /// Create a new `FunctionBuilder` for creating a native function.
     #[inline]
-    pub fn new(context: &'context mut Context, function: NativeFunction) -> Self {
+    pub fn native(context: &'context mut Context, function: NativeFunction) -> Self {
         Self {
             context,
+            function: Some(Function::Native {
                 function: function.into(),
-            name: None,
+                constructable: false,
+            }),
+            name: JsString::default(),
             length: 0,
-            callable: true,
+        }
+    }
+
+    /// Create a new `FunctionBuilder` for creating a closure function.
+    #[inline]
+    pub fn closure<F>(context: &'context mut Context, function: F) -> Self
+    where
+        F: Fn(&Value, &[Value], &mut Context) -> Result<Value, Value> + 'static,
+    {
+        Self {
+            context,
+            function: Some(Function::Closure {
+                function: Rc::new(function),
                 constructable: false,
+            }),
+            name: JsString::default(),
+            length: 0,
         }
     }
 
@@ -711,7 +728,7 @@ impl<'context> FunctionBuilder<'context> {
     where
         N: AsRef<str>,
     {
-        self.name = Some(name.as_ref().into());
+        self.name = name.as_ref().into();
         self
     }
 
@@ -726,21 +743,16 @@ impl<'context> FunctionBuilder<'context> {
         self
     }
 
-    /// Specify the whether the object function object can be called.
-    ///
-    /// The default is `true`.
-    #[inline]
-    pub fn callable(&mut self, yes: bool) -> &mut Self {
-        self.callable = yes;
-        self
-    }
-
     /// Specify the whether the object function object can be called with `new` keyword.
     ///
     /// The default is `false`.
     #[inline]
     pub fn constructable(&mut self, yes: bool) -> &mut Self {
-        self.constructable = yes;
+        match self.function.as_mut() {
+            Some(Function::Native { constructable, .. }) => *constructable = yes,
+            Some(Function::Closure { constructable, .. }) => *constructable = yes,
+            _ => unreachable!(),
+        }
         self
     }
 
@@ -748,10 +760,7 @@ impl<'context> FunctionBuilder<'context> {
     #[inline]
     pub fn build(&mut self) -> GcObject {
         let mut function = Object::function(
-            Function::BuiltIn(
-                self.function,
-                FunctionFlags::from_parameters(self.callable, self.constructable),
-            ),
+            self.function.take().unwrap(),
             self.context
                 .standard_objects()
                 .function_object()
@@ -759,11 +768,7 @@ impl<'context> FunctionBuilder<'context> {
                 .into(),
         );
         let attribute = Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::CONFIGURABLE;
-        if let Some(name) = self.name.take() {
-            function.insert_property("name", name, attribute);
-        } else {
-            function.insert_property("name", "", attribute);
-        }
+        function.insert_property("name", self.name.clone(), attribute);
         function.insert_property("length", self.length, attribute);
 
         GcObject::new(function)
@@ -772,10 +777,7 @@ impl<'context> FunctionBuilder<'context> {
     /// Initializes the `Function.prototype` function object.
     pub(crate) fn build_function_prototype(&mut self, object: &GcObject) {
         let mut object = object.borrow_mut();
-        object.data = ObjectData::Function(Function::BuiltIn(
-            self.function,
-            FunctionFlags::from_parameters(self.callable, self.constructable),
-        ));
+        object.data = ObjectData::Function(self.function.take().unwrap());
         object.set_prototype_instance(
             self.context
                 .standard_objects()
@@ -783,12 +785,8 @@ impl<'context> FunctionBuilder<'context> {
                 .prototype()
                 .into(),
         );
-        let attribute = Attribute::WRITABLE | Attribute::NON_ENUMERABLE | Attribute::PERMANENT;
-        if let Some(name) = self.name.take() {
-            object.insert_property("name", name, attribute);
-        } else {
-            object.insert_property("name", "", attribute);
-        }
+        let attribute = Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::CONFIGURABLE;
+        object.insert_property("name", self.name.clone(), attribute);
         object.insert_property("length", self.length, attribute);
     }
 }
@@ -836,10 +834,9 @@ impl<'context> ObjectInitializer<'context> {
         B: Into<FunctionBinding>,
     {
         let binding = binding.into();
-        let function = FunctionBuilder::new(self.context, function)
+        let function = FunctionBuilder::native(self.context, function)
             .name(binding.name)
             .length(length)
-            .callable(true)
             .constructable(false)
             .build();
 
@@ -876,7 +873,7 @@ pub struct ConstructorBuilder<'context> {
     constructor_function: NativeFunction,
     constructor_object: GcObject,
     prototype: GcObject,
-    name: Option<String>,
+    name: JsString,
     length: usize,
     callable: bool,
     constructable: bool,
@@ -907,7 +904,7 @@ impl<'context> ConstructorBuilder<'context> {
             constructor_object: GcObject::new(Object::default()),
             prototype: GcObject::new(Object::default()),
             length: 0,
-            name: None,
+            name: JsString::default(),
             callable: true,
             constructable: true,
             inherit: None,
@@ -926,7 +923,7 @@ impl<'context> ConstructorBuilder<'context> {
             constructor_object: object.constructor,
             prototype: object.prototype,
             length: 0,
-            name: None,
+            name: JsString::default(),
             callable: true,
             constructable: true,
             inherit: None,
@@ -940,10 +937,9 @@ impl<'context> ConstructorBuilder<'context> {
         B: Into<FunctionBinding>,
     {
         let binding = binding.into();
-        let function = FunctionBuilder::new(self.context, function)
+        let function = FunctionBuilder::native(self.context, function)
             .name(binding.name)
             .length(length)
-            .callable(true)
             .constructable(false)
             .build();
 
@@ -967,10 +963,9 @@ impl<'context> ConstructorBuilder<'context> {
         B: Into<FunctionBinding>,
     {
         let binding = binding.into();
-        let function = FunctionBuilder::new(self.context, function)
+        let function = FunctionBuilder::native(self.context, function)
             .name(binding.name)
             .length(length)
-            .callable(true)
             .constructable(false)
             .build();
 
@@ -1081,7 +1076,7 @@ impl<'context> ConstructorBuilder<'context> {
     where
         N: AsRef<str>,
     {
-        self.name = Some(name.as_ref().into());
+        self.name = name.as_ref().into();
         self
     }
 
@@ -1122,17 +1117,17 @@ impl<'context> ConstructorBuilder<'context> {
     /// Build the constructor function object.
     pub fn build(&mut self) -> GcObject {
         // Create the native function
-        let function = Function::BuiltIn(
-            self.constructor_function.into(),
-            FunctionFlags::from_parameters(self.callable, self.constructable),
-        );
+        let function = Function::Native {
+            function: self.constructor_function.into(),
+            constructable: self.constructable,
+        };
 
         let length = DataDescriptor::new(
             self.length,
             Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::CONFIGURABLE,
         );
         let name = DataDescriptor::new(
-            self.name.take().unwrap_or_else(|| String::from("[object]")),
+            self.name.clone(),
             Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::CONFIGURABLE,
         );
 

boa/src/syntax/ast/node/declaration/arrow_function_decl/mod.rs

@@ -74,11 +74,10 @@ impl ArrowFunctionDecl {
 impl Executable for ArrowFunctionDecl {
     fn run(&self, context: &mut Context) -> Result<Value> {
         context.create_function(
+            "",
             self.params().to_vec(),
             self.body().to_vec(),
-            FunctionFlags::CALLABLE
-                | FunctionFlags::CONSTRUCTABLE
-                | FunctionFlags::LEXICAL_THIS_MODE,
+            FunctionFlags::CONSTRUCTABLE | FunctionFlags::LEXICAL_THIS_MODE,
         )
     }
 }

boa/src/syntax/ast/node/declaration/function_decl/mod.rs

@@ -89,14 +89,12 @@ impl Executable for FunctionDecl {
     fn run(&self, context: &mut Context) -> Result<Value> {
         let _timer = BoaProfiler::global().start_event("FunctionDecl", "exec");
         let val = context.create_function(
+            self.name(),
             self.parameters().to_vec(),
             self.body().to_vec(),
-            FunctionFlags::CALLABLE | FunctionFlags::CONSTRUCTABLE,
+            FunctionFlags::CONSTRUCTABLE,
         )?;
 
-        // Set the name and assign it in the current environment
-        val.set_field("name", self.name(), false, context)?;
-
         if context.has_binding(self.name()) {
             context.set_mutable_binding(self.name(), val, true)?;
         } else {

boa/src/syntax/ast/node/declaration/function_expr/mod.rs

@@ -100,15 +100,12 @@ impl FunctionExpr {
 impl Executable for FunctionExpr {
     fn run(&self, context: &mut Context) -> Result<Value> {
         let val = context.create_function(
+            self.name().unwrap_or(""),
             self.parameters().to_vec(),
             self.body().to_vec(),
-            FunctionFlags::CALLABLE | FunctionFlags::CONSTRUCTABLE,
+            FunctionFlags::CONSTRUCTABLE,
         )?;
 
-        if let Some(name) = self.name() {
-            val.set_field("name", Value::from(name), false, context)?;
-        }
-
         Ok(val)
     }
 }

boa/src/value/operations.rs

@@ -11,9 +11,6 @@ impl Value {
             (Self::Integer(x), Self::Rational(y)) => Self::rational(f64::from(*x) + y),
             (Self::Rational(x), Self::Integer(y)) => Self::rational(x + f64::from(*y)),
 
-            (Self::String(ref x), Self::String(ref y)) => Self::string(format!("{}{}", x, y)),
-            (Self::String(ref x), y) => Self::string(format!("{}{}", x, y.to_string(context)?)),
-            (x, Self::String(ref y)) => Self::string(format!("{}{}", x.to_string(context)?, y)),
             (Self::String(ref x), Self::String(ref y)) => Self::from(JsString::concat(x, y)),
             (Self::String(ref x), y) => Self::from(JsString::concat(x, y.to_string(context)?)),
             (x, Self::String(ref y)) => Self::from(JsString::concat(x.to_string(context)?, y)),

boa/src/vm/mod.rs

@@ -289,13 +289,13 @@ impl<'a> Vm<'a> {
                 let value = self.pop();
                 let name = &self.code.names[index as usize];
 
-                self.context.initialize_binding(&name, value)?;
+                self.context.initialize_binding(name, value)?;
             }
             Opcode::GetName => {
                 let index = self.read::<u32>();
                 let name = &self.code.names[index as usize];
 
-                let value = self.context.get_binding_value(&name)?;
+                let value = self.context.get_binding_value(name)?;
                 self.push(value);
             }
             Opcode::SetName => {
@@ -303,16 +303,16 @@ impl<'a> Vm<'a> {
                 let value = self.pop();
                 let name = &self.code.names[index as usize];
 
-                if self.context.has_binding(&name) {
+                if self.context.has_binding(name) {
                     // Binding already exists
-                    self.context.set_mutable_binding(&name, value, true)?;
+                    self.context.set_mutable_binding(name, value, true)?;
                 } else {
                     self.context.create_mutable_binding(
                         name.to_string(),
                         true,
                         VariableScope::Function,
                     )?;
-                    self.context.initialize_binding(&name, value)?;
+                    self.context.initialize_binding(name, value)?;
                 }
             }
             Opcode::Jump => {

boa_tester/src/exec/mod.rs

@@ -137,7 +137,7 @@ impl Test {
                 Outcome::Positive => {
                     // TODO: implement async and add `harness/doneprintHandle.js` to the includes.
 
-                    match self.set_up_env(&harness, strict) {
+                    match self.set_up_env(harness, strict) {
                         Ok(mut context) => {
                             let res = context.eval(&self.content.as_ref());
 
@@ -183,7 +183,7 @@ impl Test {
                     if let Err(e) = parse(&self.content.as_ref(), strict) {
                         (false, format!("Uncaught {}", e))
                     } else {
-                        match self.set_up_env(&harness, strict) {
+                        match self.set_up_env(harness, strict) {
                             Ok(mut context) => match context.eval(&self.content.as_ref()) {
                                 Ok(res) => (false, format!("{}", res.display())),
                                 Err(e) => {