diff --git a/boa_ast/src/operations.rs b/boa_ast/src/operations.rs
index 09d7634d06b..09dab5a6745 100644
--- a/boa_ast/src/operations.rs
+++ b/boa_ast/src/operations.rs
@@ -2156,3 +2156,63 @@ impl<'ast> Visitor<'ast> for ReturnsValueVisitor {
         ControlFlow::Continue(())
     }
 }
+
+/// Returns `true` if the given statement can optimize local variables.
+#[must_use]
+pub fn can_optimize_local_variables<'a, N>(node: &'a N) -> bool
+where
+    &'a N: Into<NodeRef<'a>>,
+{
+    CanOptimizeLocalVariables.visit(node.into()).is_continue()
+}
+
+/// The [`Visitor`] used for [`returns_value`].
+#[derive(Debug)]
+struct CanOptimizeLocalVariables;
+
+impl<'ast> Visitor<'ast> for CanOptimizeLocalVariables {
+    type BreakTy = ();
+
+    fn visit_with(&mut self, _node: &'ast crate::statement::With) -> ControlFlow<Self::BreakTy> {
+        ControlFlow::Break(())
+    }
+
+    fn visit_call(&mut self, node: &'ast crate::expression::Call) -> ControlFlow<Self::BreakTy> {
+        if let Expression::Identifier(identifier) = node.function() {
+            if identifier.sym() == Sym::EVAL {
+                return ControlFlow::Break(());
+            }
+        }
+
+        try_break!(node.function().visit_with(self));
+
+        for arg in node.args() {
+            try_break!(arg.visit_with(self));
+        }
+
+        ControlFlow::Continue(())
+    }
+
+    fn visit_function(&mut self, _node: &'ast Function) -> ControlFlow<Self::BreakTy> {
+        ControlFlow::Break(())
+    }
+
+    fn visit_arrow_function(&mut self, _node: &'ast ArrowFunction) -> ControlFlow<Self::BreakTy> {
+        ControlFlow::Break(())
+    }
+
+    fn visit_async_function(&mut self, _node: &'ast AsyncFunction) -> ControlFlow<Self::BreakTy> {
+        ControlFlow::Break(())
+    }
+
+    fn visit_async_arrow_function(
+        &mut self,
+        _node: &'ast AsyncArrowFunction,
+    ) -> ControlFlow<Self::BreakTy> {
+        ControlFlow::Break(())
+    }
+
+    fn visit_class(&mut self, _node: &'ast Class) -> ControlFlow<Self::BreakTy> {
+        ControlFlow::Break(())
+    }
+}
diff --git a/boa_engine/src/bytecompiler/class.rs b/boa_engine/src/bytecompiler/class.rs
index 1bc57de76ca..3902b50ae5e 100644
--- a/boa_engine/src/bytecompiler/class.rs
+++ b/boa_engine/src/bytecompiler/class.rs
@@ -30,7 +30,9 @@ impl ByteCompiler<'_, '_> {
             Some(name) if class.has_binding_identifier() => {
                 let env_index = self.push_compile_environment(false);
                 self.create_immutable_binding(name, true);
-                self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+                if !self.can_optimize_local_variables {
+                    self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+                }
                 true
             }
             _ => false,
@@ -39,7 +41,7 @@ impl ByteCompiler<'_, '_> {
         let mut compiler = ByteCompiler::new(
             class_name,
             true,
-            self.json_parse,
+            self.json_parse(),
             self.current_environment.clone(),
             self.context,
         );
@@ -276,7 +278,7 @@ impl ByteCompiler<'_, '_> {
                     let mut field_compiler = ByteCompiler::new(
                         Sym::EMPTY_STRING,
                         true,
-                        self.json_parse,
+                        self.json_parse(),
                         self.current_environment.clone(),
                         self.context,
                     );
@@ -310,7 +312,7 @@ impl ByteCompiler<'_, '_> {
                     let mut field_compiler = ByteCompiler::new(
                         class_name,
                         true,
-                        self.json_parse,
+                        self.json_parse(),
                         self.current_environment.clone(),
                         self.context,
                     );
@@ -354,7 +356,7 @@ impl ByteCompiler<'_, '_> {
                     let mut field_compiler = ByteCompiler::new(
                         class_name,
                         true,
-                        self.json_parse,
+                        self.json_parse(),
                         self.current_environment.clone(),
                         self.context,
                     );
@@ -591,7 +593,9 @@ impl ByteCompiler<'_, '_> {
 
         if class_env {
             self.pop_compile_environment();
-            self.emit_opcode(Opcode::PopEnvironment);
+            if !self.can_optimize_local_variables {
+                self.emit_opcode(Opcode::PopEnvironment);
+            }
         }
 
         self.emit_opcode(Opcode::PopPrivateEnvironment);
diff --git a/boa_engine/src/bytecompiler/declarations.rs b/boa_engine/src/bytecompiler/declarations.rs
index 2ebfdd7a405..582ff26a76d 100644
--- a/boa_engine/src/bytecompiler/declarations.rs
+++ b/boa_engine/src/bytecompiler/declarations.rs
@@ -570,9 +570,13 @@ impl ByteCompiler<'_, '_> {
 
                                     // ii. Perform ! varEnv.InitializeBinding(F, undefined).
                                     let binding = self.initialize_mutable_binding(f, true);
-                                    let index = self.get_or_insert_binding(binding);
                                     self.emit_opcode(Opcode::PushUndefined);
-                                    self.emit_with_varying_operand(Opcode::DefInitVar, index);
+                                    self.get_or_insert_binding(binding).emit(
+                                        Opcode::SetLocal,
+                                        Opcode::SetGlobalName,
+                                        Opcode::DefInitVar,
+                                        self,
+                                    );
                                 }
                             }
 
@@ -742,10 +746,12 @@ impl ByteCompiler<'_, '_> {
                 if binding_exists {
                     // 1. Perform ! varEnv.SetMutableBinding(fn, fo, false).
                     match self.set_mutable_binding(name) {
-                        Ok(binding) => {
-                            let index = self.get_or_insert_binding(binding);
-                            self.emit_with_varying_operand(Opcode::SetName, index);
-                        }
+                        Ok(binding) => self.get_or_insert_binding(binding).emit(
+                            Opcode::SetLocal,
+                            Opcode::SetGlobalName,
+                            Opcode::SetName,
+                            self,
+                        ),
                         Err(BindingLocatorError::MutateImmutable) => {
                             let index = self.get_or_insert_name(name);
                             self.emit_with_varying_operand(Opcode::ThrowMutateImmutable, index);
@@ -760,8 +766,12 @@ impl ByteCompiler<'_, '_> {
                     // 3. Perform ! varEnv.InitializeBinding(fn, fo).
                     self.create_mutable_binding(name, !strict);
                     let binding = self.initialize_mutable_binding(name, !strict);
-                    let index = self.get_or_insert_binding(binding);
-                    self.emit_with_varying_operand(Opcode::DefInitVar, index);
+                    self.get_or_insert_binding(binding).emit(
+                        Opcode::SetLocal,
+                        Opcode::SetGlobalName,
+                        Opcode::DefInitVar,
+                        self,
+                    );
                 }
             }
         }
@@ -785,9 +795,13 @@ impl ByteCompiler<'_, '_> {
                     // 3. Perform ! varEnv.InitializeBinding(vn, undefined).
                     self.create_mutable_binding(name, !strict);
                     let binding = self.initialize_mutable_binding(name, !strict);
-                    let index = self.get_or_insert_binding(binding);
                     self.emit_opcode(Opcode::PushUndefined);
-                    self.emit_with_varying_operand(Opcode::DefInitVar, index);
+                    self.get_or_insert_binding(binding).emit(
+                        Opcode::SetLocal,
+                        Opcode::SetGlobalName,
+                        Opcode::DefInitVar,
+                        self,
+                    );
                 }
             }
         }
@@ -919,6 +933,13 @@ impl ByteCompiler<'_, '_> {
         // NOTE(HalidOdat): Has been moved up, so "arguments" gets registed as
         //     the first binding in the environment with index 0.
         if arguments_object_needed {
+            if !strict {
+                self.can_optimize_local_variables = false;
+            }
+
+            let can_optimize_local_variables = self.can_optimize_local_variables;
+            self.can_optimize_local_variables = false;
+
             // Note: This happens at runtime.
             // a. If strict is true or simpleParameterList is false, then
             //     i. Let ao be CreateUnmappedArgumentsObject(argumentsList).
@@ -941,6 +962,10 @@ impl ByteCompiler<'_, '_> {
                 self.create_mutable_binding(arguments, false);
             }
 
+            let binding = self.get_binding_value(arguments);
+            self.get_or_insert_binding(binding);
+            self.can_optimize_local_variables = can_optimize_local_variables;
+
             self.code_block_flags |= CodeBlockFlags::NEEDS_ARGUMENTS_OBJECT;
         }
 
@@ -1017,7 +1042,7 @@ impl ByteCompiler<'_, '_> {
         }
 
         if generator {
-            self.emit(Opcode::Generator, &[Operand::U8(self.in_async().into())]);
+            self.emit(Opcode::Generator, &[Operand::Bool(self.is_async())]);
             self.emit_opcode(Opcode::Pop);
         }
 
@@ -1031,7 +1056,9 @@ impl ByteCompiler<'_, '_> {
             // b. Let varEnv be NewDeclarativeEnvironment(env).
             // c. Set the VariableEnvironment of calleeContext to varEnv.
             let env_index = self.push_compile_environment(false);
-            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+            if !self.can_optimize_local_variables {
+                self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+            }
             env_label = true;
 
             // d. Let instantiatedVarNames be a new empty List.
@@ -1056,15 +1083,23 @@ impl ByteCompiler<'_, '_> {
                     else {
                         // a. Let initialValue be ! env.GetBindingValue(n, false).
                         let binding = self.get_binding_value(n);
-                        let index = self.get_or_insert_binding(binding);
-                        self.emit_with_varying_operand(Opcode::GetName, index);
+                        self.get_or_insert_binding(binding).emit(
+                            Opcode::GetLocal,
+                            Opcode::GetGlobalName,
+                            Opcode::GetName,
+                            self,
+                        );
                     }
 
                     // 5. Perform ! varEnv.InitializeBinding(n, initialValue).
                     let binding = self.initialize_mutable_binding(n, true);
-                    let index = self.get_or_insert_binding(binding);
                     self.emit_opcode(Opcode::PushUndefined);
-                    self.emit_with_varying_operand(Opcode::DefInitVar, index);
+                    self.get_or_insert_binding(binding).emit(
+                        Opcode::SetLocal,
+                        Opcode::SetGlobalName,
+                        Opcode::DefInitVar,
+                        self,
+                    );
 
                     // 6. NOTE: A var with the same name as a formal parameter initially has
                     //          the same value as the corresponding initialized parameter.
@@ -1089,9 +1124,13 @@ impl ByteCompiler<'_, '_> {
 
                     // 3. Perform ! env.InitializeBinding(n, undefined).
                     let binding = self.initialize_mutable_binding(n, true);
-                    let index = self.get_or_insert_binding(binding);
                     self.emit_opcode(Opcode::PushUndefined);
-                    self.emit_with_varying_operand(Opcode::DefInitVar, index);
+                    self.get_or_insert_binding(binding).emit(
+                        Opcode::SetLocal,
+                        Opcode::SetGlobalName,
+                        Opcode::DefInitVar,
+                        self,
+                    );
                 }
             }
 
@@ -1121,9 +1160,13 @@ impl ByteCompiler<'_, '_> {
 
                         // b. Perform ! varEnv.InitializeBinding(F, undefined).
                         let binding = self.initialize_mutable_binding(f, true);
-                        let index = self.get_or_insert_binding(binding);
                         self.emit_opcode(Opcode::PushUndefined);
-                        self.emit_with_varying_operand(Opcode::DefInitVar, index);
+                        self.get_or_insert_binding(binding).emit(
+                            Opcode::SetLocal,
+                            Opcode::SetGlobalName,
+                            Opcode::DefInitVar,
+                            self,
+                        );
 
                         // c. Append F to instantiatedVarNames.
                         instantiated_var_names.push(f);
diff --git a/boa_engine/src/bytecompiler/expression/assign.rs b/boa_engine/src/bytecompiler/expression/assign.rs
index 9efc49e2b23..0e18241de26 100644
--- a/boa_engine/src/bytecompiler/expression/assign.rs
+++ b/boa_engine/src/bytecompiler/expression/assign.rs
@@ -1,5 +1,5 @@
 use crate::{
-    bytecompiler::{Access, ByteCompiler, Operand},
+    bytecompiler::{Access, ByteCompiler, EnvironmentAccess, Operand},
     environments::BindingLocatorError,
     vm::{BindingOpcode, Opcode},
 };
@@ -56,14 +56,26 @@ impl ByteCompiler<'_, '_> {
             match access {
                 Access::Variable { name } => {
                     let binding = self.get_binding_value(name);
-                    let index = self.get_or_insert_binding(binding);
                     let lex = self.current_environment.is_lex_binding(name);
 
-                    if lex {
-                        self.emit_with_varying_operand(Opcode::GetName, index);
-                    } else {
-                        self.emit_with_varying_operand(Opcode::GetNameAndLocator, index);
-                    }
+                    let is_fast = match self.get_or_insert_binding(binding) {
+                        EnvironmentAccess::Fast { index } => {
+                            self.emit_with_varying_operand(Opcode::GetLocal, index);
+                            true
+                        }
+                        EnvironmentAccess::Global { index } => {
+                            self.emit_with_varying_operand(Opcode::GetGlobalName, index);
+                            true
+                        }
+                        EnvironmentAccess::Slow { index } => {
+                            if lex {
+                                self.emit_with_varying_operand(Opcode::GetName, index);
+                            } else {
+                                self.emit_with_varying_operand(Opcode::GetNameAndLocator, index);
+                            }
+                            false
+                        }
+                    };
 
                     if short_circuit {
                         early_exit = Some(self.emit_opcode_with_operand(opcode));
@@ -75,12 +87,14 @@ impl ByteCompiler<'_, '_> {
                     if use_expr {
                         self.emit_opcode(Opcode::Dup);
                     }
-                    if lex {
+                    if lex || is_fast {
                         match self.set_mutable_binding(name) {
-                            Ok(binding) => {
-                                let index = self.get_or_insert_binding(binding);
-                                self.emit_with_varying_operand(Opcode::SetName, index);
-                            }
+                            Ok(binding) => self.get_or_insert_binding(binding).emit(
+                                Opcode::SetLocal,
+                                Opcode::SetGlobalName,
+                                Opcode::SetName,
+                                self,
+                            ),
                             Err(BindingLocatorError::MutateImmutable) => {
                                 let index = self.get_or_insert_name(name);
                                 self.emit_with_varying_operand(Opcode::ThrowMutateImmutable, index);
diff --git a/boa_engine/src/bytecompiler/expression/mod.rs b/boa_engine/src/bytecompiler/expression/mod.rs
index a9ae59ce2ed..5a9867ca2d9 100644
--- a/boa_engine/src/bytecompiler/expression/mod.rs
+++ b/boa_engine/src/bytecompiler/expression/mod.rs
@@ -175,7 +175,7 @@ impl ByteCompiler<'_, '_> {
                 // stack: value
 
                 if r#yield.delegate() {
-                    if self.in_async() {
+                    if self.is_async() {
                         self.emit_opcode(Opcode::GetAsyncIterator);
                     } else {
                         self.emit_opcode(Opcode::GetIterator);
@@ -192,14 +192,14 @@ impl ByteCompiler<'_, '_> {
                     let (throw_method_undefined, return_method_undefined) =
                         self.emit_opcode_with_two_operands(Opcode::GeneratorDelegateNext);
 
-                    if self.in_async() {
+                    if self.is_async() {
                         self.emit_opcode(Opcode::Pop);
                         self.emit_opcode(Opcode::Await);
                     }
 
                     let (return_gen, exit) =
                         self.emit_opcode_with_two_operands(Opcode::GeneratorDelegateResume);
-                    if self.in_async() {
+                    if self.is_async() {
                         self.emit_opcode(Opcode::IteratorValue);
                         self.async_generator_yield();
                     } else {
@@ -210,7 +210,7 @@ impl ByteCompiler<'_, '_> {
 
                     self.patch_jump(return_gen);
                     self.patch_jump(return_method_undefined);
-                    if self.in_async() {
+                    if self.is_async() {
                         self.emit_opcode(Opcode::Await);
                         self.emit_opcode(Opcode::Pop);
                     }
@@ -219,7 +219,7 @@ impl ByteCompiler<'_, '_> {
                     self.r#return(true);
 
                     self.patch_jump(throw_method_undefined);
-                    self.iterator_close(self.in_async());
+                    self.iterator_close(self.is_async());
                     self.emit_opcode(Opcode::Throw);
 
                     self.patch_jump(exit);
diff --git a/boa_engine/src/bytecompiler/expression/object_literal.rs b/boa_engine/src/bytecompiler/expression/object_literal.rs
index 10dea9d1665..39451470e45 100644
--- a/boa_engine/src/bytecompiler/expression/object_literal.rs
+++ b/boa_engine/src/bytecompiler/expression/object_literal.rs
@@ -24,7 +24,7 @@ impl ByteCompiler<'_, '_> {
                     PropertyName::Literal(name) => {
                         self.compile_expr(expr, true);
                         let index = self.get_or_insert_name((*name).into());
-                        if *name == Sym::__PROTO__ && !self.json_parse {
+                        if *name == Sym::__PROTO__ && !self.json_parse() {
                             self.emit_opcode(Opcode::SetPrototype);
                         } else {
                             self.emit_with_varying_operand(Opcode::DefineOwnPropertyByName, index);
diff --git a/boa_engine/src/bytecompiler/expression/unary.rs b/boa_engine/src/bytecompiler/expression/unary.rs
index 662d403afc5..9efcc20a82c 100644
--- a/boa_engine/src/bytecompiler/expression/unary.rs
+++ b/boa_engine/src/bytecompiler/expression/unary.rs
@@ -28,8 +28,12 @@ impl ByteCompiler<'_, '_> {
                 match unary.target().flatten() {
                     Expression::Identifier(identifier) => {
                         let binding = self.get_binding_value(*identifier);
-                        let index = self.get_or_insert_binding(binding);
-                        self.emit_with_varying_operand(Opcode::GetNameOrUndefined, index);
+                        self.get_or_insert_binding(binding).emit(
+                            Opcode::GetLocal,
+                            Opcode::GetGlobalNameOrUndefined,
+                            Opcode::GetNameOrUndefined,
+                            self,
+                        );
                     }
                     expr => self.compile_expr(expr, true),
                 }
diff --git a/boa_engine/src/bytecompiler/expression/update.rs b/boa_engine/src/bytecompiler/expression/update.rs
index 110cc6b4400..8a1b099ccb4 100644
--- a/boa_engine/src/bytecompiler/expression/update.rs
+++ b/boa_engine/src/bytecompiler/expression/update.rs
@@ -1,5 +1,5 @@
 use crate::{
-    bytecompiler::{Access, ByteCompiler, Operand},
+    bytecompiler::{Access, ByteCompiler, EnvironmentAccess, Operand},
     environments::BindingLocatorError,
     vm::Opcode,
 };
@@ -24,14 +24,26 @@ impl ByteCompiler<'_, '_> {
         match Access::from_update_target(update.target()) {
             Access::Variable { name } => {
                 let binding = self.get_binding_value(name);
-                let index = self.get_or_insert_binding(binding);
                 let lex = self.current_environment.is_lex_binding(name);
 
-                if lex {
-                    self.emit_with_varying_operand(Opcode::GetName, index);
-                } else {
-                    self.emit_with_varying_operand(Opcode::GetNameAndLocator, index);
-                }
+                let is_fast = match self.get_or_insert_binding(binding) {
+                    EnvironmentAccess::Fast { index } => {
+                        self.emit_with_varying_operand(Opcode::GetLocal, index);
+                        true
+                    }
+                    EnvironmentAccess::Global { index } => {
+                        self.emit_with_varying_operand(Opcode::GetGlobalName, index);
+                        true
+                    }
+                    EnvironmentAccess::Slow { index } => {
+                        if lex {
+                            self.emit_with_varying_operand(Opcode::GetName, index);
+                        } else {
+                            self.emit_with_varying_operand(Opcode::GetNameAndLocator, index);
+                        }
+                        false
+                    }
+                };
 
                 self.emit_opcode(opcode);
                 if post {
@@ -40,12 +52,14 @@ impl ByteCompiler<'_, '_> {
                     self.emit_opcode(Opcode::Dup);
                 }
 
-                if lex {
+                if lex || is_fast {
                     match self.set_mutable_binding(name) {
-                        Ok(binding) => {
-                            let index = self.get_or_insert_binding(binding);
-                            self.emit_with_varying_operand(Opcode::SetName, index);
-                        }
+                        Ok(binding) => self.get_or_insert_binding(binding).emit(
+                            Opcode::SetLocal,
+                            Opcode::SetGlobalName,
+                            Opcode::SetName,
+                            self,
+                        ),
                         Err(BindingLocatorError::MutateImmutable) => {
                             let index = self.get_or_insert_name(name);
                             self.emit_with_varying_operand(Opcode::ThrowMutateImmutable, index);
diff --git a/boa_engine/src/bytecompiler/function.rs b/boa_engine/src/bytecompiler/function.rs
index be072a6198a..f4fbdefe820 100644
--- a/boa_engine/src/bytecompiler/function.rs
+++ b/boa_engine/src/bytecompiler/function.rs
@@ -2,12 +2,15 @@ use std::rc::Rc;
 
 use crate::{
     builtins::function::ThisMode,
-    bytecompiler::ByteCompiler,
+    bytecompiler::{ByteCompiler, ByteCompilerFlags},
     environments::CompileTimeEnvironment,
     vm::{CodeBlock, CodeBlockFlags, Opcode},
     Context,
 };
-use boa_ast::function::{FormalParameterList, FunctionBody};
+use boa_ast::{
+    function::{FormalParameterList, FunctionBody},
+    operations::can_optimize_local_variables,
+};
 use boa_gc::Gc;
 use boa_interner::Sym;
 
@@ -21,6 +24,8 @@ pub(crate) struct FunctionCompiler {
     strict: bool,
     arrow: bool,
     binding_identifier: Option<Sym>,
+
+    can_optimize: bool,
 }
 
 impl FunctionCompiler {
@@ -33,6 +38,7 @@ impl FunctionCompiler {
             strict: false,
             arrow: false,
             binding_identifier: None,
+            can_optimize: true,
         }
     }
 
@@ -77,6 +83,12 @@ impl FunctionCompiler {
         self
     }
 
+    /// Indicate if the function can be optimized.
+    pub(crate) const fn can_optimize(mut self, can_optimize: bool) -> Self {
+        self.can_optimize = can_optimize;
+        self
+    }
+
     /// Compile a function statement list and it's parameters into bytecode.
     pub(crate) fn compile(
         mut self,
@@ -91,8 +103,11 @@ impl FunctionCompiler {
 
         let mut compiler = ByteCompiler::new(self.name, self.strict, false, outer_env, context);
         compiler.length = length;
-        compiler.in_async = self.r#async;
-        compiler.in_generator = self.generator;
+
+        compiler.flags.set(ByteCompilerFlags::ASYNC, self.r#async);
+        compiler
+            .flags
+            .set(ByteCompilerFlags::GENERATOR, self.generator);
 
         if self.arrow {
             compiler.this_mode = ThisMode::Lexical;
@@ -107,6 +122,9 @@ impl FunctionCompiler {
         // Function environment
         let _ = compiler.push_compile_environment(true);
 
+        compiler.function_environment_index =
+            Some(compiler.current_environment.environment_index());
+
         // Taken from:
         //  - 15.9.3 Runtime Semantics: EvaluateAsyncConciseBody: <https://tc39.es/ecma262/#sec-runtime-semantics-evaluateasyncconcisebody>
         //  - 15.8.4 Runtime Semantics: EvaluateAsyncFunctionBody: <https://tc39.es/ecma262/#sec-runtime-semantics-evaluateasyncfunctionbody>
@@ -115,7 +133,7 @@ impl FunctionCompiler {
         // `FunctionDeclarationInstantiation` (so they are propagated).
         //
         // See: 15.6.2 Runtime Semantics: EvaluateAsyncGeneratorBody: https://tc39.es/ecma262/#sec-runtime-semantics-evaluateasyncgeneratorbody
-        if compiler.in_async() && !compiler.in_generator() {
+        if compiler.is_async() && !compiler.is_generator() {
             // 1. Let promiseCapability be ! NewPromiseCapability(%Promise%).
             //
             // Note: If the promise capability is already set, then we do nothing.
@@ -123,6 +141,9 @@ impl FunctionCompiler {
             // ExecuteAsyncModule ( module ): <https://tc39.es/ecma262/#sec-execute-async-module>
             compiler.emit_opcode(Opcode::CreatePromiseCapability);
 
+            // Note: We set it to one so we don't pop return value when we return.
+            compiler.current_stack_value_count += 1;
+
             // 2. Let declResult be Completion(FunctionDeclarationInstantiation(functionObject, argumentsList)).
             //
             // Note: We push an exception handler so we catch exceptions that are thrown by the
@@ -132,6 +153,19 @@ impl FunctionCompiler {
             compiler.async_handler = Some(compiler.push_handler());
         }
 
+        let can_optimize_params = can_optimize_local_variables(parameters);
+        let can_optimize_body = can_optimize_local_variables(body);
+        // println!("Can optimize params: {can_optimize_params}");
+        // println!("Can optimize body: {can_optimize_body}");
+
+        let can_optimize =
+            can_optimize_params && can_optimize_body && parameters.is_simple() && self.can_optimize;
+
+        println!("Can optimize function: {can_optimize}");
+
+        compiler.can_optimize_local_variables =
+            can_optimize && compiler.function_environment_index.is_some();
+
         let (env_label, additional_env) = compiler.function_declaration_instantiation(
             body,
             parameters,
@@ -144,10 +178,10 @@ impl FunctionCompiler {
         // - 27.6.3.2 AsyncGeneratorStart ( generator, generatorBody ): <https://tc39.es/ecma262/#sec-asyncgeneratorstart>
         //
         // Note: We do handle exceptions thrown by generator body in `AsyncGeneratorStart`.
-        if compiler.in_generator() {
+        if compiler.is_generator() {
             assert!(compiler.async_handler.is_none());
 
-            if compiler.in_async() {
+            if compiler.is_async() {
                 // Patched in `ByteCompiler::finish()`.
                 compiler.async_handler = Some(compiler.push_handler());
             }
diff --git a/boa_engine/src/bytecompiler/jump_control.rs b/boa_engine/src/bytecompiler/jump_control.rs
index 85708c90a98..e0ac73fdbdc 100644
--- a/boa_engine/src/bytecompiler/jump_control.rs
+++ b/boa_engine/src/bytecompiler/jump_control.rs
@@ -102,6 +102,10 @@ impl JumpRecord {
                     return;
                 }
                 JumpRecordAction::PopEnvironments { count } => {
+                    if compiler.can_optimize_local_variables {
+                        continue;
+                    }
+
                     for _ in 0..count {
                         compiler.emit_opcode(Opcode::PopEnvironment);
                     }
@@ -129,7 +133,7 @@ impl JumpRecord {
                     compiler.emit_opcode(Opcode::SetReturnValue);
                 }
 
-                match (compiler.in_async(), compiler.in_generator()) {
+                match (compiler.is_async(), compiler.is_generator()) {
                     // Taken from:
                     //  - 27.6.3.2 AsyncGeneratorStart ( generator, generatorBody ): https://tc39.es/ecma262/#sec-asyncgeneratorstart
                     //
diff --git a/boa_engine/src/bytecompiler/mod.rs b/boa_engine/src/bytecompiler/mod.rs
index a8b734a8ada..160da883f00 100644
--- a/boa_engine/src/bytecompiler/mod.rs
+++ b/boa_engine/src/bytecompiler/mod.rs
@@ -23,6 +23,7 @@ use crate::{
     },
     Context, JsBigInt, JsString, JsValue,
 };
+use bitflags::bitflags;
 use boa_ast::{
     declaration::{Binding, LexicalDeclaration, VarDeclaration},
     expression::{
@@ -229,6 +230,58 @@ pub(crate) enum Operand {
     Varying(u32),
 }
 
+#[derive(Debug, Clone, Copy)]
+pub(crate) enum EnvironmentAccess {
+    Fast { index: u32 },
+    Global { index: u32 },
+    Slow { index: u32 },
+}
+
+impl EnvironmentAccess {
+    pub(crate) fn emit<L, G, S>(
+        self,
+        local: L,
+        global: G,
+        slow: S,
+        compiler: &mut ByteCompiler<'_, '_>,
+    ) where
+        L: Into<Option<Opcode>>,
+        G: Into<Option<Opcode>>,
+        S: Into<Option<Opcode>>,
+    {
+        let local = local.into();
+        let global = global.into();
+        let slow = slow.into();
+
+        match self {
+            Self::Fast { index } if local.is_some() => {
+                compiler
+                    .emit_with_varying_operand(local.expect("there should be an opcode"), index);
+            }
+            Self::Global { index } if global.is_some() => compiler
+                .emit_with_varying_operand(global.expect("there should be an opcode"), index),
+            Self::Slow { index } if slow.is_some() => {
+                compiler.emit_with_varying_operand(slow.expect("there should be an opcode"), index);
+            }
+            _ => {}
+        }
+    }
+}
+
+bitflags! {
+    /// Flags for [`ByteCompiler`].
+    #[derive(Clone, Copy, Debug)]
+    pub(crate) struct ByteCompilerFlags: u8 {
+        const ASYNC = 0b0000_0001;
+        const GENERATOR = 0b0000_0010;
+        const HAS_WITH_STATEMENT = 0b0000_0100;
+        const IN_WITH_STATEMENT = 0b0000_1000;
+        const IN_EVAL = 0b0001_0000;
+        const HAS_EVAL = 0b0010_0000;
+        const JSON_PARSE = 0b0100_0000;
+    }
+}
+
 /// The [`ByteCompiler`] is used to compile ECMAScript AST from [`boa_ast`] to bytecode.
 #[derive(Debug)]
 #[allow(clippy::struct_excessive_bools)]
@@ -272,16 +325,19 @@ pub struct ByteCompiler<'ctx, 'host> {
     handlers: ThinVec<Handler>,
     literals_map: FxHashMap<Literal, u32>,
     names_map: FxHashMap<Identifier, u32>,
-    bindings_map: FxHashMap<BindingLocator, u32>,
+    bindings_map: FxHashMap<BindingLocator, EnvironmentAccess>,
     jump_info: Vec<JumpControlInfo>,
-    pub(crate) in_async: bool,
-    in_generator: bool,
+
+    pub(crate) flags: ByteCompilerFlags,
+    can_optimize_local_variables: bool,
+    #[allow(dead_code)]
+    fast_local_variable_count: u32,
+    function_environment_index: Option<u32>,
 
     /// Used to handle exception throws that escape the async function types.
     ///
     /// Async functions and async generator functions, need to be closed and resolved.
     pub(crate) async_handler: Option<u32>,
-    json_parse: bool,
 
     // TODO: remove when we separate scripts from the context
     context: &'ctx mut Context<'host>,
@@ -307,6 +363,9 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
     ) -> ByteCompiler<'ctx, 'host> {
         let mut code_block_flags = CodeBlockFlags::empty();
         code_block_flags.set(CodeBlockFlags::STRICT, strict);
+
+        let mut flags = ByteCompilerFlags::empty();
+        flags.set(ByteCompilerFlags::JSON_PARSE, json_parse);
         Self {
             function_name: name,
             length: 0,
@@ -328,13 +387,15 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
             names_map: FxHashMap::default(),
             bindings_map: FxHashMap::default(),
             jump_info: Vec::new(),
-            in_async: false,
-            in_generator: false,
+            can_optimize_local_variables: false,
+            fast_local_variable_count: 0,
+            function_environment_index: None,
             async_handler: None,
-            json_parse,
             current_environment,
             context,
 
+            flags,
+
             #[cfg(feature = "annex-b")]
             annex_b_function_names: Vec::new(),
         }
@@ -344,16 +405,20 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
         self.code_block_flags.contains(CodeBlockFlags::STRICT)
     }
 
-    pub(crate) const fn in_async(&self) -> bool {
-        self.in_async
+    pub(crate) const fn is_async(&self) -> bool {
+        self.flags.contains(ByteCompilerFlags::ASYNC)
     }
 
-    pub(crate) const fn in_generator(&self) -> bool {
-        self.in_generator
+    pub(crate) const fn is_generator(&self) -> bool {
+        self.flags.contains(ByteCompilerFlags::GENERATOR)
     }
 
-    pub(crate) const fn in_async_generator(&self) -> bool {
-        self.in_async() && self.in_generator()
+    pub(crate) const fn is_async_generator(&self) -> bool {
+        self.is_async() && self.is_generator()
+    }
+
+    pub(crate) const fn json_parse(&self) -> bool {
+        self.flags.contains(ByteCompilerFlags::JSON_PARSE)
     }
 
     pub(crate) fn interner(&self) -> &Interner {
@@ -394,31 +459,55 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
     }
 
     #[inline]
-    pub(crate) fn get_or_insert_binding(&mut self, binding: BindingLocator) -> u32 {
+    pub(crate) fn get_or_insert_binding(&mut self, binding: BindingLocator) -> EnvironmentAccess {
         if let Some(index) = self.bindings_map.get(&binding) {
             return *index;
         }
 
+        if let Some(function_environment_index) = self.function_environment_index {
+            if !binding.is_global()
+                && self.can_optimize_local_variables
+                && function_environment_index <= binding.environment_index()
+            {
+                let index = self.fast_local_variable_count;
+                self.fast_local_variable_count += 1;
+
+                println!("Fast binding {binding:?} at {index}");
+
+                self.bindings_map
+                    .insert(binding, EnvironmentAccess::Fast { index });
+                return EnvironmentAccess::Fast { index };
+            }
+
+            if binding.is_global() && !binding.is_lex() && self.can_optimize_local_variables {
+                let index = self.get_or_insert_name(binding.name());
+                return EnvironmentAccess::Global { index };
+            }
+        }
+
         let index = self.bindings.len() as u32;
         self.bindings.push(binding);
-        self.bindings_map.insert(binding, index);
-        index
+        self.bindings_map
+            .insert(binding, EnvironmentAccess::Slow { index });
+        EnvironmentAccess::Slow { index }
     }
 
     fn emit_binding(&mut self, opcode: BindingOpcode, name: Identifier) {
         match opcode {
             BindingOpcode::Var => {
                 let binding = self.initialize_mutable_binding(name, true);
-                let index = self.get_or_insert_binding(binding);
-                self.emit_with_varying_operand(Opcode::DefVar, index);
+                self.get_or_insert_binding(binding)
+                    .emit(None, None, Opcode::DefVar, self);
             }
             BindingOpcode::InitVar => {
                 if self.has_binding(name) {
                     match self.set_mutable_binding(name) {
-                        Ok(binding) => {
-                            let index = self.get_or_insert_binding(binding);
-                            self.emit_with_varying_operand(Opcode::DefInitVar, index);
-                        }
+                        Ok(binding) => self.get_or_insert_binding(binding).emit(
+                            Opcode::SetLocal,
+                            Opcode::SetGlobalName,
+                            Opcode::DefInitVar,
+                            self,
+                        ),
                         Err(BindingLocatorError::MutateImmutable) => {
                             let index = self.get_or_insert_name(name);
                             self.emit_with_varying_operand(Opcode::ThrowMutateImmutable, index);
@@ -429,25 +518,39 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
                     }
                 } else {
                     let binding = self.initialize_mutable_binding(name, true);
-                    let index = self.get_or_insert_binding(binding);
-                    self.emit_with_varying_operand(Opcode::DefInitVar, index);
+                    self.get_or_insert_binding(binding).emit(
+                        Opcode::SetLocal,
+                        Opcode::SetGlobalName,
+                        Opcode::DefInitVar,
+                        self,
+                    );
                 };
             }
             BindingOpcode::InitLet => {
                 let binding = self.initialize_mutable_binding(name, false);
-                let index = self.get_or_insert_binding(binding);
-                self.emit_with_varying_operand(Opcode::PutLexicalValue, index);
+                self.get_or_insert_binding(binding).emit(
+                    Opcode::SetLocal,
+                    Opcode::SetGlobalName,
+                    Opcode::PutLexicalValue,
+                    self,
+                );
             }
             BindingOpcode::InitConst => {
                 let binding = self.initialize_immutable_binding(name);
-                let index = self.get_or_insert_binding(binding);
-                self.emit_with_varying_operand(Opcode::PutLexicalValue, index);
+                self.get_or_insert_binding(binding).emit(
+                    Opcode::SetLocal,
+                    Opcode::SetGlobalName,
+                    Opcode::PutLexicalValue,
+                    self,
+                );
             }
             BindingOpcode::SetName => match self.set_mutable_binding(name) {
-                Ok(binding) => {
-                    let index = self.get_or_insert_binding(binding);
-                    self.emit_with_varying_operand(Opcode::SetName, index);
-                }
+                Ok(binding) => self.get_or_insert_binding(binding).emit(
+                    Opcode::SetLocal,
+                    Opcode::SetGlobalName,
+                    Opcode::SetName,
+                    self,
+                ),
                 Err(BindingLocatorError::MutateImmutable) => {
                     let index = self.get_or_insert_name(name);
                     self.emit_with_varying_operand(Opcode::ThrowMutateImmutable, index);
@@ -699,8 +802,12 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
         match access {
             Access::Variable { name } => {
                 let binding = self.get_binding_value(name);
-                let index = self.get_or_insert_binding(binding);
-                self.emit_with_varying_operand(Opcode::GetName, index);
+                self.get_or_insert_binding(binding).emit(
+                    Opcode::GetLocal,
+                    Opcode::GetGlobalName,
+                    Opcode::GetName,
+                    self,
+                );
             }
             Access::Property { access } => match access {
                 PropertyAccess::Simple(access) => match access.field() {
@@ -764,24 +871,32 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
         match access {
             Access::Variable { name } => {
                 let binding = self.get_binding_value(name);
-                let index = self.get_or_insert_binding(binding);
                 let lex = self.current_environment.is_lex_binding(name);
 
-                if !lex {
-                    self.emit_with_varying_operand(Opcode::GetLocator, index);
-                }
+                let is_fast = match self.get_or_insert_binding(binding) {
+                    EnvironmentAccess::Fast { index: _ }
+                    | EnvironmentAccess::Global { index: _ } => true,
+                    EnvironmentAccess::Slow { index } => {
+                        if !lex {
+                            self.emit_with_varying_operand(Opcode::GetLocator, index);
+                        }
+                        false
+                    }
+                };
 
                 expr_fn(self, 0);
                 if use_expr {
                     self.emit(Opcode::Dup, &[]);
                 }
 
-                if lex {
+                if lex || is_fast {
                     match self.set_mutable_binding(name) {
-                        Ok(binding) => {
-                            let index = self.get_or_insert_binding(binding);
-                            self.emit_with_varying_operand(Opcode::SetName, index);
-                        }
+                        Ok(binding) => self.get_or_insert_binding(binding).emit(
+                            Opcode::SetLocal,
+                            Opcode::SetGlobalName,
+                            Opcode::SetName,
+                            self,
+                        ),
                         Err(BindingLocatorError::MutateImmutable) => {
                             let index = self.get_or_insert_name(name);
                             self.emit_with_varying_operand(Opcode::ThrowMutateImmutable, index);
@@ -877,8 +992,15 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
             },
             Access::Variable { name } => {
                 let binding = self.get_binding_value(name);
-                let index = self.get_or_insert_binding(binding);
-                self.emit_with_varying_operand(Opcode::DeleteName, index);
+                match self.get_or_insert_binding(binding) {
+                    EnvironmentAccess::Fast { index: _ } => self.emit_opcode(Opcode::PushFalse),
+                    EnvironmentAccess::Global { index } => {
+                        self.emit_with_varying_operand(Opcode::DeleteGlobalName, index);
+                    }
+                    EnvironmentAccess::Slow { index } => {
+                        self.emit_with_varying_operand(Opcode::DeleteName, index);
+                    }
+                }
             }
             Access::This => {
                 self.emit_opcode(Opcode::PushTrue);
@@ -1192,14 +1314,20 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
                     .expect("function declaration must have name");
                 if self.annex_b_function_names.contains(&name) {
                     let binding = self.get_binding_value(name);
-                    let index = self.get_or_insert_binding(binding);
-                    self.emit_with_varying_operand(Opcode::GetName, index);
+                    self.get_or_insert_binding(binding).emit(
+                        Opcode::GetLocal,
+                        Opcode::GetGlobalName,
+                        Opcode::GetName,
+                        self,
+                    );
 
                     match self.set_mutable_binding_var(name) {
-                        Ok(binding) => {
-                            let index = self.get_or_insert_binding(binding);
-                            self.emit_with_varying_operand(Opcode::SetName, index);
-                        }
+                        Ok(binding) => self.get_or_insert_binding(binding).emit(
+                            Opcode::SetLocal,
+                            Opcode::SetGlobalName,
+                            Opcode::SetName,
+                            self,
+                        ),
                         Err(BindingLocatorError::MutateImmutable) => {
                             let index = self.get_or_insert_name(name);
                             self.emit_with_varying_operand(Opcode::ThrowMutateImmutable, index);
@@ -1249,6 +1377,7 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
             .strict(self.strict())
             .arrow(arrow)
             .binding_identifier(binding_identifier)
+            .can_optimize(self.can_optimize_local_variables)
             .compile(
                 parameters,
                 body,
@@ -1533,6 +1662,12 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
             .utf16()
             .into();
 
+        if self.can_optimize_local_variables {
+            for handler in &mut self.handlers {
+                handler.stack_count += self.fast_local_variable_count;
+            }
+        }
+
         CodeBlock {
             name,
             length: self.length,
@@ -1546,6 +1681,7 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
             compile_environments: self.compile_environments.into_boxed_slice(),
             handlers: self.handlers,
             flags: Cell::new(self.code_block_flags),
+            local_variable_count: self.fast_local_variable_count,
         }
     }
 
diff --git a/boa_engine/src/bytecompiler/statement/block.rs b/boa_engine/src/bytecompiler/statement/block.rs
index 5982dfd0731..219fc9492f2 100644
--- a/boa_engine/src/bytecompiler/statement/block.rs
+++ b/boa_engine/src/bytecompiler/statement/block.rs
@@ -5,12 +5,16 @@ impl ByteCompiler<'_, '_> {
     /// Compile a [`Block`] `boa_ast` node
     pub(crate) fn compile_block(&mut self, block: &Block, use_expr: bool) {
         let env_index = self.push_compile_environment(false);
-        self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+        if !self.can_optimize_local_variables {
+            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+        }
 
         self.block_declaration_instantiation(block);
         self.compile_statement_list(block.statement_list(), use_expr, true);
 
         self.pop_compile_environment();
-        self.emit_opcode(Opcode::PopEnvironment);
+        if !self.can_optimize_local_variables {
+            self.emit_opcode(Opcode::PopEnvironment);
+        }
     }
 }
diff --git a/boa_engine/src/bytecompiler/statement/loop.rs b/boa_engine/src/bytecompiler/statement/loop.rs
index 4088a7e3b1c..3d28ab8b2e3 100644
--- a/boa_engine/src/bytecompiler/statement/loop.rs
+++ b/boa_engine/src/bytecompiler/statement/loop.rs
@@ -32,7 +32,12 @@ impl ByteCompiler<'_, '_> {
                 }
                 ForLoopInitializer::Lexical(decl) => {
                     let env_index = self.push_compile_environment(false);
-                    self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+                    if !self.can_optimize_local_variables {
+                        self.emit_with_varying_operand(
+                            Opcode::PushDeclarativeEnvironment,
+                            env_index,
+                        );
+                    }
                     has_lexical_environment_binding = true;
 
                     let names = bound_names(decl);
@@ -66,16 +71,28 @@ impl ByteCompiler<'_, '_> {
             .expect("jump_control must exist as it was just pushed")
             .set_start_address(start_address);
 
-        if let Some((let_binding_indices, env_index)) = &let_binding_indices {
-            for index in let_binding_indices {
-                self.emit_with_varying_operand(Opcode::GetName, *index);
-            }
+        if !self.can_optimize_local_variables {
+            if let Some((let_binding_indices, env_index)) = &let_binding_indices {
+                for index in let_binding_indices {
+                    index.emit(
+                        Opcode::GetLocal,
+                        Opcode::GetGlobalName,
+                        Opcode::GetName,
+                        self,
+                    );
+                }
 
-            self.emit_opcode(Opcode::PopEnvironment);
-            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, *env_index);
+                self.emit_opcode(Opcode::PopEnvironment);
+                self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, *env_index);
 
-            for index in let_binding_indices.iter().rev() {
-                self.emit_with_varying_operand(Opcode::PutLexicalValue, *index);
+                for index in let_binding_indices.iter().rev() {
+                    index.emit(
+                        Opcode::SetLocal,
+                        Opcode::SetGlobalName,
+                        Opcode::PutLexicalValue,
+                        self,
+                    );
+                }
             }
         }
 
@@ -103,7 +120,9 @@ impl ByteCompiler<'_, '_> {
 
         if has_lexical_environment_binding {
             self.pop_compile_environment();
-            self.emit_opcode(Opcode::PopEnvironment);
+            if !self.can_optimize_local_variables {
+                self.emit_opcode(Opcode::PopEnvironment);
+            }
         }
     }
 
@@ -131,7 +150,9 @@ impl ByteCompiler<'_, '_> {
             self.compile_expr(for_in_loop.target(), true);
         } else {
             let env_index = self.push_compile_environment(false);
-            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+            if !self.can_optimize_local_variables {
+                self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+            }
 
             for name in &initializer_bound_names {
                 self.create_mutable_binding(*name, false);
@@ -139,7 +160,9 @@ impl ByteCompiler<'_, '_> {
             self.compile_expr(for_in_loop.target(), true);
 
             self.pop_compile_environment();
-            self.emit_opcode(Opcode::PopEnvironment);
+            if !self.can_optimize_local_variables {
+                self.emit_opcode(Opcode::PopEnvironment);
+            }
         }
 
         let early_exit = self.jump_if_null_or_undefined();
@@ -157,7 +180,9 @@ impl ByteCompiler<'_, '_> {
 
         if !initializer_bound_names.is_empty() {
             let env_index = self.push_compile_environment(false);
-            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+            if !self.can_optimize_local_variables {
+                self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+            }
         }
 
         match for_in_loop.initializer() {
@@ -212,7 +237,9 @@ impl ByteCompiler<'_, '_> {
 
         if !initializer_bound_names.is_empty() {
             self.pop_compile_environment();
-            self.emit_opcode(Opcode::PopEnvironment);
+            if !self.can_optimize_local_variables {
+                self.emit_opcode(Opcode::PopEnvironment);
+            }
         }
 
         self.emit(Opcode::Jump, &[Operand::U32(start_address)]);
@@ -243,7 +270,9 @@ impl ByteCompiler<'_, '_> {
             self.compile_expr(for_of_loop.iterable(), true);
         } else {
             let env_index = self.push_compile_environment(false);
-            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+            if !self.can_optimize_local_variables {
+                self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+            }
 
             for name in &initializer_bound_names {
                 self.create_mutable_binding(*name, false);
@@ -251,7 +280,9 @@ impl ByteCompiler<'_, '_> {
             self.compile_expr(for_of_loop.iterable(), true);
 
             self.pop_compile_environment();
-            self.emit_opcode(Opcode::PopEnvironment);
+            if !self.can_optimize_local_variables {
+                self.emit_opcode(Opcode::PopEnvironment);
+            }
         }
 
         if for_of_loop.r#await() {
@@ -281,17 +312,22 @@ impl ByteCompiler<'_, '_> {
 
         if !initializer_bound_names.is_empty() {
             let env_index = self.push_compile_environment(false);
-            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+
+            if !self.can_optimize_local_variables {
+                self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+            }
         };
 
         let mut handler_index = None;
         match for_of_loop.initializer() {
             IterableLoopInitializer::Identifier(ref ident) => {
                 match self.set_mutable_binding(*ident) {
-                    Ok(binding) => {
-                        let index = self.get_or_insert_binding(binding);
-                        self.emit_with_varying_operand(Opcode::DefInitVar, index);
-                    }
+                    Ok(binding) => self.get_or_insert_binding(binding).emit(
+                        Opcode::SetLocal,
+                        Opcode::SetGlobalName,
+                        Opcode::DefInitVar,
+                        self,
+                    ),
                     Err(BindingLocatorError::MutateImmutable) => {
                         let index = self.get_or_insert_name(*ident);
                         self.emit_with_varying_operand(Opcode::ThrowMutateImmutable, index);
@@ -377,7 +413,9 @@ impl ByteCompiler<'_, '_> {
 
         if !initializer_bound_names.is_empty() {
             self.pop_compile_environment();
-            self.emit_opcode(Opcode::PopEnvironment);
+            if !self.can_optimize_local_variables {
+                self.emit_opcode(Opcode::PopEnvironment);
+            }
         }
 
         self.emit(Opcode::Jump, &[Operand::U32(start_address)]);
diff --git a/boa_engine/src/bytecompiler/statement/mod.rs b/boa_engine/src/bytecompiler/statement/mod.rs
index 81f7b3d45aa..91c332ea6a7 100644
--- a/boa_engine/src/bytecompiler/statement/mod.rs
+++ b/boa_engine/src/bytecompiler/statement/mod.rs
@@ -65,7 +65,7 @@ impl ByteCompiler<'_, '_> {
             Statement::Return(ret) => {
                 if let Some(expr) = ret.target() {
                     self.compile_expr(expr, true);
-                    if self.in_async_generator() {
+                    if self.is_async_generator() {
                         self.emit_opcode(Opcode::Await);
                         self.emit_opcode(Opcode::GeneratorNext);
                     }
diff --git a/boa_engine/src/bytecompiler/statement/switch.rs b/boa_engine/src/bytecompiler/statement/switch.rs
index fd007840671..bf203e121c8 100644
--- a/boa_engine/src/bytecompiler/statement/switch.rs
+++ b/boa_engine/src/bytecompiler/statement/switch.rs
@@ -7,7 +7,9 @@ impl ByteCompiler<'_, '_> {
         self.compile_expr(switch.val(), true);
 
         let env_index = self.push_compile_environment(false);
-        self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+        if !self.can_optimize_local_variables {
+            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+        }
 
         self.block_declaration_instantiation(switch);
 
@@ -51,6 +53,8 @@ impl ByteCompiler<'_, '_> {
         self.pop_switch_control_info();
 
         self.pop_compile_environment();
-        self.emit_opcode(Opcode::PopEnvironment);
+        if !self.can_optimize_local_variables {
+            self.emit_opcode(Opcode::PopEnvironment);
+        }
     }
 }
diff --git a/boa_engine/src/bytecompiler/statement/try.rs b/boa_engine/src/bytecompiler/statement/try.rs
index 07a6bb1b1c4..888d8b66595 100644
--- a/boa_engine/src/bytecompiler/statement/try.rs
+++ b/boa_engine/src/bytecompiler/statement/try.rs
@@ -38,7 +38,7 @@ impl ByteCompiler<'_, '_> {
 
         // If it has a finally but no catch and we are in a generator, then we still need it
         // to handle `return()` call on generators.
-        let catch_handler = if has_finally && (self.in_generator() || has_catch) {
+        let catch_handler = if has_finally && (self.is_generator() || has_catch) {
             self.current_stack_value_count += 2;
             Some(self.push_handler())
         } else {
@@ -50,7 +50,7 @@ impl ByteCompiler<'_, '_> {
             self.compile_catch_stmt(catch, has_finally, use_expr);
         } else {
             // Note: implicit !has_catch
-            if self.in_generator() && has_finally {
+            if self.is_generator() && has_finally {
                 // Is this a generator `return()` empty exception?
                 //
                 // This is false because when the `Exception` opcode is executed,
@@ -77,7 +77,7 @@ impl ByteCompiler<'_, '_> {
             }
 
             // Note: implicit has_finally
-            if !has_catch && self.in_generator() {
+            if !has_catch && self.is_generator() {
                 // Is this a generator `return()` empty exception?
                 self.emit_opcode(Opcode::PushTrue);
             }
@@ -110,9 +110,10 @@ impl ByteCompiler<'_, '_> {
 
     pub(crate) fn compile_catch_stmt(&mut self, catch: &Catch, _has_finally: bool, use_expr: bool) {
         // stack: exception
-
         let env_index = self.push_compile_environment(false);
-        self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+        if !self.can_optimize_local_variables {
+            self.emit_with_varying_operand(Opcode::PushDeclarativeEnvironment, env_index);
+        }
 
         if let Some(binding) = catch.parameter() {
             match binding {
@@ -134,7 +135,9 @@ impl ByteCompiler<'_, '_> {
         self.compile_catch_finally_block(catch.block(), use_expr);
 
         self.pop_compile_environment();
-        self.emit_opcode(Opcode::PopEnvironment);
+        if !self.can_optimize_local_variables {
+            self.emit_opcode(Opcode::PopEnvironment);
+        }
     }
 
     pub(crate) fn compile_finally_stmt(&mut self, finally: &Finally, has_catch: bool) {
@@ -150,7 +153,7 @@ impl ByteCompiler<'_, '_> {
 
         if has_catch {
             self.emit_opcode(Opcode::ReThrow);
-        } else if self.in_generator() {
+        } else if self.is_generator() {
             let is_generator_exit = self.jump_if_true();
             self.emit_opcode(Opcode::Throw);
             self.patch_jump(is_generator_exit);
diff --git a/boa_engine/src/bytecompiler/utils.rs b/boa_engine/src/bytecompiler/utils.rs
index 6ba4335fe2c..8319fb31a42 100644
--- a/boa_engine/src/bytecompiler/utils.rs
+++ b/boa_engine/src/bytecompiler/utils.rs
@@ -50,7 +50,7 @@ impl ByteCompiler<'_, '_> {
         let start = self.next_opcode_location();
         self.emit_opcode(Opcode::IteratorStackEmpty);
         let empty = self.jump_if_true();
-        self.iterator_close(self.in_async_generator());
+        self.iterator_close(self.is_async_generator());
         self.emit(Opcode::Jump, &[Operand::U32(start)]);
         self.patch_jump(empty);
     }
@@ -65,7 +65,7 @@ impl ByteCompiler<'_, '_> {
     /// [yield]: https://tc39.es/ecma262/#sec-yield
     pub(super) fn r#yield(&mut self) {
         // 1. Let generatorKind be GetGeneratorKind().
-        if self.in_async() {
+        if self.is_async() {
             // 2. If generatorKind is async, return ? AsyncGeneratorYield(? Await(value)).
             self.emit_opcode(Opcode::Await);
             self.emit_opcode(Opcode::GeneratorNext);
diff --git a/boa_engine/src/environments/compile.rs b/boa_engine/src/environments/compile.rs
index f0dad91db2a..d911a322222 100644
--- a/boa_engine/src/environments/compile.rs
+++ b/boa_engine/src/environments/compile.rs
@@ -94,20 +94,19 @@ impl CompileTimeEnvironment {
 
     /// Get the locator for a binding name.
     pub(crate) fn get_binding(&self, name: Identifier) -> Option<BindingLocator> {
-        self.bindings
-            .borrow()
-            .get(&name)
-            .map(|binding| BindingLocator::declarative(name, self.environment_index, binding.index))
+        self.bindings.borrow().get(&name).map(|binding| {
+            BindingLocator::declarative(name, self.environment_index, binding.index, binding.lex)
+        })
     }
 
     /// Get the locator for a binding name in this and all outer environments.
     pub(crate) fn get_binding_recursive(&self, name: Identifier) -> BindingLocator {
         if let Some(binding) = self.bindings.borrow().get(&name) {
-            BindingLocator::declarative(name, self.environment_index, binding.index)
+            BindingLocator::declarative(name, self.environment_index, binding.index, binding.lex)
         } else if let Some(outer) = &self.outer {
             outer.get_binding_recursive(name)
         } else {
-            BindingLocator::global(name)
+            BindingLocator::global(name, false)
         }
     }
 
@@ -223,12 +222,19 @@ impl CompileTimeEnvironment {
             }
             self.bindings.borrow().get(&name).map_or_else(
                 || outer.initialize_mutable_binding(name, function_scope),
-                |binding| BindingLocator::declarative(name, self.environment_index, binding.index),
+                |binding| {
+                    BindingLocator::declarative(
+                        name,
+                        self.environment_index,
+                        binding.index,
+                        binding.lex,
+                    )
+                },
             )
         } else if let Some(binding) = self.bindings.borrow().get(&name) {
-            BindingLocator::declarative(name, self.environment_index, binding.index)
+            BindingLocator::declarative(name, self.environment_index, binding.index, binding.lex)
         } else {
-            BindingLocator::global(name)
+            BindingLocator::global(name, false)
         }
     }
 
@@ -240,7 +246,7 @@ impl CompileTimeEnvironment {
     pub(crate) fn initialize_immutable_binding(&self, name: Identifier) -> BindingLocator {
         let bindings = self.bindings.borrow();
         let binding = bindings.get(&name).expect("binding must exist");
-        BindingLocator::declarative(name, self.environment_index, binding.index)
+        BindingLocator::declarative(name, self.environment_index, binding.index, binding.lex)
     }
 
     /// Return the binding locator for a mutable binding.
@@ -249,13 +255,16 @@ impl CompileTimeEnvironment {
         name: Identifier,
     ) -> Result<BindingLocator, BindingLocatorError> {
         Ok(match self.bindings.borrow().get(&name) {
-            Some(binding) if binding.mutable => {
-                BindingLocator::declarative(name, self.environment_index, binding.index)
-            }
+            Some(binding) if binding.mutable => BindingLocator::declarative(
+                name,
+                self.environment_index,
+                binding.index,
+                binding.lex,
+            ),
             Some(binding) if binding.strict => return Err(BindingLocatorError::MutateImmutable),
             Some(_) => return Err(BindingLocatorError::Silent),
             None => self.outer.as_ref().map_or_else(
-                || Ok(BindingLocator::global(name)),
+                || Ok(BindingLocator::global(name, false)),
                 |outer| outer.set_mutable_binding_recursive(name),
             )?,
         })
@@ -269,19 +278,22 @@ impl CompileTimeEnvironment {
     ) -> Result<BindingLocator, BindingLocatorError> {
         if !self.is_function() {
             return self.outer.as_ref().map_or_else(
-                || Ok(BindingLocator::global(name)),
+                || Ok(BindingLocator::global(name, false)),
                 |outer| outer.set_mutable_binding_var_recursive(name),
             );
         }
 
         Ok(match self.bindings.borrow().get(&name) {
-            Some(binding) if binding.mutable => {
-                BindingLocator::declarative(name, self.environment_index, binding.index)
-            }
+            Some(binding) if binding.mutable => BindingLocator::declarative(
+                name,
+                self.environment_index,
+                binding.index,
+                binding.lex,
+            ),
             Some(binding) if binding.strict => return Err(BindingLocatorError::MutateImmutable),
             Some(_) => return Err(BindingLocatorError::Silent),
             None => self.outer.as_ref().map_or_else(
-                || Ok(BindingLocator::global(name)),
+                || Ok(BindingLocator::global(name, false)),
                 |outer| outer.set_mutable_binding_var_recursive(name),
             )?,
         })
@@ -291,4 +303,8 @@ impl CompileTimeEnvironment {
     pub(crate) fn outer(&self) -> Option<Rc<Self>> {
         self.outer.clone()
     }
+
+    pub(crate) const fn environment_index(&self) -> u32 {
+        self.environment_index
+    }
 }
diff --git a/boa_engine/src/environments/runtime/mod.rs b/boa_engine/src/environments/runtime/mod.rs
index d89a01a6b58..c0f0d3ccbc0 100644
--- a/boa_engine/src/environments/runtime/mod.rs
+++ b/boa_engine/src/environments/runtime/mod.rs
@@ -474,6 +474,7 @@ pub(crate) struct BindingLocator {
     environment_index: u32,
     binding_index: u32,
     global: bool,
+    lex: bool,
 }
 
 unsafe impl Trace for BindingLocator {
@@ -486,22 +487,25 @@ impl BindingLocator {
         name: Identifier,
         environment_index: u32,
         binding_index: u32,
+        lex: bool,
     ) -> Self {
         Self {
             name,
             environment_index,
             binding_index,
             global: false,
+            lex,
         }
     }
 
     /// Creates a binding locator that indicates that the binding is on the global object.
-    pub(super) const fn global(name: Identifier) -> Self {
+    pub(super) const fn global(name: Identifier, lex: bool) -> Self {
         Self {
             name,
             environment_index: 0,
             binding_index: 0,
             global: true,
+            lex,
         }
     }
 
@@ -515,6 +519,11 @@ impl BindingLocator {
         self.global
     }
 
+    /// Returns if the binding is a lexical binding.
+    pub(crate) const fn is_lex(&self) -> bool {
+        self.lex
+    }
+
     /// Returns the environment index of the binding.
     pub(crate) const fn environment_index(&self) -> u32 {
         self.environment_index
diff --git a/boa_engine/src/module/source.rs b/boa_engine/src/module/source.rs
index 068ba259efa..1d086f29313 100644
--- a/boa_engine/src/module/source.rs
+++ b/boa_engine/src/module/source.rs
@@ -22,7 +22,7 @@ use rustc_hash::{FxHashMap, FxHashSet, FxHasher};
 
 use crate::{
     builtins::{promise::PromiseCapability, Promise},
-    bytecompiler::{ByteCompiler, FunctionSpec},
+    bytecompiler::{ByteCompiler, ByteCompilerFlags, FunctionSpec},
     environments::{BindingLocator, CompileTimeEnvironment, EnvironmentStack},
     module::ModuleKind,
     object::{FunctionObjectBuilder, JsPromise, RecursionLimiter},
@@ -1415,7 +1415,7 @@ impl SourceTextModule {
         let mut compiler =
             ByteCompiler::new(Sym::MAIN, true, false, module_compile_env.clone(), context);
 
-        compiler.in_async = true;
+        compiler.flags |= ByteCompilerFlags::ASYNC;
         compiler.async_handler = Some(compiler.push_handler());
 
         let mut imports = Vec::new();
@@ -1499,9 +1499,13 @@ impl SourceTextModule {
                         compiler.create_mutable_binding(name, false);
                         // 2. Perform ! env.InitializeBinding(dn, undefined).
                         let binding = compiler.initialize_mutable_binding(name, false);
-                        let index = compiler.get_or_insert_binding(binding);
                         compiler.emit_opcode(Opcode::PushUndefined);
-                        compiler.emit_with_varying_operand(Opcode::DefInitVar, index);
+                        compiler.get_or_insert_binding(binding).emit(
+                            Opcode::SetLocal,
+                            Opcode::SetGlobalName,
+                            Opcode::DefInitVar,
+                            &mut compiler,
+                        );
                         // 3. Append dn to declaredVarNames.
                         declared_var_names.push(name);
                     }
diff --git a/boa_engine/src/vm/code_block.rs b/boa_engine/src/vm/code_block.rs
index df17b441e38..503b8467599 100644
--- a/boa_engine/src/vm/code_block.rs
+++ b/boa_engine/src/vm/code_block.rs
@@ -163,6 +163,8 @@ pub struct CodeBlock {
     // TODO(#3034): Maybe changing this to Gc after garbage collection would be better than Rc.
     #[unsafe_ignore_trace]
     pub(crate) compile_environments: Box<[Rc<CompileTimeEnvironment>]>,
+
+    pub(crate) local_variable_count: u32,
 }
 
 /// ---- `CodeBlock` public API ----
@@ -185,6 +187,7 @@ impl CodeBlock {
             params: FormalParameterList::default(),
             handlers: ThinVec::default(),
             compile_environments: Box::default(),
+            local_variable_count: 0,
         }
     }
 
@@ -428,8 +431,6 @@ impl CodeBlock {
             | Instruction::SetPropertySetterByName { index }
             | Instruction::DefineClassStaticSetterByName { index }
             | Instruction::DefineClassSetterByName { index }
-            | Instruction::InPrivate { index }
-            | Instruction::ThrowMutateImmutable { index }
             | Instruction::DeletePropertyByName { index }
             | Instruction::SetPrivateField { index }
             | Instruction::DefinePrivateField { index }
@@ -440,7 +441,13 @@ impl CodeBlock {
             | Instruction::PushClassFieldPrivate { index }
             | Instruction::PushClassPrivateGetter { index }
             | Instruction::PushClassPrivateSetter { index }
-            | Instruction::PushClassPrivateMethod { index } => {
+            | Instruction::PushClassPrivateMethod { index }
+            | Instruction::InPrivate { index }
+            | Instruction::ThrowMutateImmutable { index }
+            | Instruction::GetGlobalName { index }
+            | Instruction::GetGlobalNameOrUndefined { index }
+            | Instruction::SetGlobalName { index }
+            | Instruction::DeleteGlobalName { index } => {
                 format!(
                     "{:04}: '{}'",
                     index.value(),
@@ -463,6 +470,9 @@ impl CodeBlock {
             Instruction::CreateIteratorResult { done } => {
                 format!("done: {done}")
             }
+            Instruction::GetLocal { index } | Instruction::SetLocal { index } => {
+                index.value().to_string()
+            }
             Instruction::Pop
             | Instruction::Dup
             | Instruction::Swap
@@ -637,13 +647,7 @@ impl CodeBlock {
             | Instruction::Reserved49
             | Instruction::Reserved50
             | Instruction::Reserved51
-            | Instruction::Reserved52
-            | Instruction::Reserved53
-            | Instruction::Reserved54
-            | Instruction::Reserved55
-            | Instruction::Reserved56
-            | Instruction::Reserved57
-            | Instruction::Reserved58 => unreachable!("Reserved opcodes are unrechable"),
+            | Instruction::Reserved52 => unreachable!("Reserved opcodes are unrechable"),
         }
     }
 }
@@ -1123,6 +1127,7 @@ impl JsObject {
 
         let argument_count = args.len();
         let parameters_count = code.params.as_ref().len();
+        let local_variable_count = code.local_variable_count;
 
         let frame = CallFrame::new(code, script_or_module, Some(self.clone()))
             .with_argument_count(argument_count as u32)
@@ -1130,6 +1135,10 @@ impl JsObject {
 
         context.vm.push_frame(frame);
 
+        for _ in 0..local_variable_count {
+            context.vm.push(JsValue::undefined());
+        }
+
         // Push function arguments to the stack.
         for _ in argument_count..parameters_count {
             context.vm.push(JsValue::undefined());
@@ -1274,6 +1283,7 @@ impl JsObject {
 
         let argument_count = args.len();
         let parameters_count = code.params.as_ref().len();
+        let local_variable_count = code.local_variable_count;
 
         context.vm.push_frame(
             CallFrame::new(code, script_or_module, Some(self.clone()))
@@ -1281,6 +1291,10 @@ impl JsObject {
                 .with_env_fp(environments_len as u32),
         );
 
+        for _ in 0..local_variable_count {
+            context.vm.push(JsValue::undefined());
+        }
+
         // Push function arguments to the stack.
         for _ in argument_count..parameters_count {
             context.vm.push(JsValue::undefined());
diff --git a/boa_engine/src/vm/flowgraph/mod.rs b/boa_engine/src/vm/flowgraph/mod.rs
index 5152f1b200d..3ad3deb7798 100644
--- a/boa_engine/src/vm/flowgraph/mod.rs
+++ b/boa_engine/src/vm/flowgraph/mod.rs
@@ -260,7 +260,9 @@ impl CodeBlock {
                 | Instruction::GetNameAndLocator { .. }
                 | Instruction::GetNameOrUndefined { .. }
                 | Instruction::SetName { .. }
-                | Instruction::DeleteName { .. } => {
+                | Instruction::DeleteName { .. }
+                | Instruction::GetLocal { .. }
+                | Instruction::SetLocal { .. } => {
                     graph.add_node(previous_pc, NodeShape::None, label.into(), Color::None);
                     graph.add_edge(previous_pc, pc, None, Color::None, EdgeStyle::Line);
                 }
@@ -287,7 +289,11 @@ impl CodeBlock {
                 | Instruction::PushClassPrivateSetter { .. }
                 | Instruction::PushClassPrivateMethod { .. }
                 | Instruction::InPrivate { .. }
-                | Instruction::ThrowMutateImmutable { .. } => {
+                | Instruction::ThrowMutateImmutable { .. }
+                | Instruction::GetGlobalName { .. }
+                | Instruction::SetGlobalName { .. }
+                | Instruction::GetGlobalNameOrUndefined { .. }
+                | Instruction::DeleteGlobalName { .. } => {
                     graph.add_node(previous_pc, NodeShape::None, label.into(), Color::None);
                     graph.add_edge(previous_pc, pc, None, Color::None, EdgeStyle::Line);
                 }
@@ -516,13 +522,7 @@ impl CodeBlock {
                 | Instruction::Reserved49
                 | Instruction::Reserved50
                 | Instruction::Reserved51
-                | Instruction::Reserved52
-                | Instruction::Reserved53
-                | Instruction::Reserved54
-                | Instruction::Reserved55
-                | Instruction::Reserved56
-                | Instruction::Reserved57
-                | Instruction::Reserved58 => unreachable!("Reserved opcodes are unrechable"),
+                | Instruction::Reserved52 => unreachable!("Reserved opcodes are unrechable"),
             }
         }
 
diff --git a/boa_engine/src/vm/opcode/control_flow/return.rs b/boa_engine/src/vm/opcode/control_flow/return.rs
index 8db9cab8707..4ecdd2be140 100644
--- a/boa_engine/src/vm/opcode/control_flow/return.rs
+++ b/boa_engine/src/vm/opcode/control_flow/return.rs
@@ -54,3 +54,79 @@ impl Operation for SetReturnValue {
         Ok(CompletionType::Normal)
     }
 }
+
+/// `GetLocal` implements the Opcode Operation for `Opcode::GetLocal`
+///
+/// Operation:
+///  - Sets the return value of a function.
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct GetLocal;
+
+impl GetLocal {
+    #[allow(clippy::unnecessary_wraps)]
+    fn operation(context: &mut Context<'_>, offset: usize) -> JsResult<CompletionType> {
+        let index = context.vm.frame().fp as usize + offset;
+
+        let value = context.vm.stack[index].clone();
+        context.vm.push(value);
+        Ok(CompletionType::Normal)
+    }
+}
+
+impl Operation for GetLocal {
+    const NAME: &'static str = "GetLocal";
+    const INSTRUCTION: &'static str = "INST - GetLocal";
+
+    fn execute(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let offset = context.vm.read::<u8>() as usize;
+        Self::operation(context, offset)
+    }
+
+    fn execute_with_u16_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let offset = context.vm.read::<u16>() as usize;
+        Self::operation(context, offset)
+    }
+
+    fn execute_with_u32_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let offset = context.vm.read::<u32>() as usize;
+        Self::operation(context, offset)
+    }
+}
+
+/// `SetLocal` implements the Opcode Operation for `Opcode::SetLocal`
+///
+/// Operation:
+///  - Sets the return value of a function.
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct SetLocal;
+
+impl SetLocal {
+    #[allow(clippy::unnecessary_wraps)]
+    fn operation(context: &mut Context<'_>, offset: usize) -> JsResult<CompletionType> {
+        let index = context.vm.frame().fp as usize + offset;
+
+        let value = context.vm.pop();
+        context.vm.stack[index] = value;
+        Ok(CompletionType::Normal)
+    }
+}
+
+impl Operation for SetLocal {
+    const NAME: &'static str = "SetLocal";
+    const INSTRUCTION: &'static str = "INST - SetLocal";
+
+    fn execute(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let offset = context.vm.read::<u8>() as usize;
+        Self::operation(context, offset)
+    }
+
+    fn execute_with_u16_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let offset = context.vm.read::<u16>() as usize;
+        Self::operation(context, offset)
+    }
+
+    fn execute_with_u32_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let offset = context.vm.read::<u32>() as usize;
+        Self::operation(context, offset)
+    }
+}
diff --git a/boa_engine/src/vm/opcode/delete/mod.rs b/boa_engine/src/vm/opcode/delete/mod.rs
index ddeb0ec1d60..aec52b26ef8 100644
--- a/boa_engine/src/vm/opcode/delete/mod.rs
+++ b/boa_engine/src/vm/opcode/delete/mod.rs
@@ -99,8 +99,45 @@ impl Operation for DeleteName {
     const INSTRUCTION: &'static str = "INST - DeleteName";
 
     fn execute(context: &mut Context<'_>) -> JsResult<CompletionType> {
-        let index = context.vm.read::<u8>();
-        Self::operation(context, index as usize)
+        let index = context.vm.read::<u8>() as usize;
+        Self::operation(context, index)
+    }
+
+    fn execute_with_u16_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let index = context.vm.read::<u16>() as usize;
+        Self::operation(context, index)
+    }
+
+    fn execute_with_u32_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let index = context.vm.read::<u32>() as usize;
+        Self::operation(context, index)
+    }
+}
+
+/// `DeleteGlobalName` implements the Opcode Operation for `Opcode::DeleteGlobalName`
+///
+/// Operation:
+///  - Deletes a global property.
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct DeleteGlobalName;
+
+impl DeleteGlobalName {
+    fn operation(context: &mut Context<'_>, index: usize) -> JsResult<CompletionType> {
+        let key = context.vm.frame().code_block().names[index].clone().into();
+        let deleted = context.global_object().__delete__(&key, context)?;
+
+        context.vm.push(deleted);
+        Ok(CompletionType::Normal)
+    }
+}
+
+impl Operation for DeleteGlobalName {
+    const NAME: &'static str = "DeleteGlobalName";
+    const INSTRUCTION: &'static str = "INST - DeleteGlobalName";
+
+    fn execute(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let index = context.vm.read::<u8>() as usize;
+        Self::operation(context, index)
     }
 
     fn execute_with_u16_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
@@ -109,8 +146,8 @@ impl Operation for DeleteName {
     }
 
     fn execute_with_u32_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
-        let index = context.vm.read::<u32>();
-        Self::operation(context, index as usize)
+        let index = context.vm.read::<u32>() as usize;
+        Self::operation(context, index)
     }
 }
 
diff --git a/boa_engine/src/vm/opcode/get/name.rs b/boa_engine/src/vm/opcode/get/name.rs
index 31812939706..b269c08321f 100644
--- a/boa_engine/src/vm/opcode/get/name.rs
+++ b/boa_engine/src/vm/opcode/get/name.rs
@@ -33,8 +33,8 @@ impl Operation for GetName {
     const INSTRUCTION: &'static str = "INST - GetName";
 
     fn execute(context: &mut Context<'_>) -> JsResult<CompletionType> {
-        let index = context.vm.read::<u8>();
-        Self::operation(context, index as usize)
+        let index = context.vm.read::<u8>() as usize;
+        Self::operation(context, index)
     }
 
     fn execute_with_u16_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
@@ -43,8 +43,93 @@ impl Operation for GetName {
     }
 
     fn execute_with_u32_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
-        let index = context.vm.read::<u32>();
-        Self::operation(context, index as usize)
+        let index = context.vm.read::<u32>() as usize;
+        Self::operation(context, index)
+    }
+}
+
+/// `GetGlobalName` implements the Opcode Operation for `Opcode::GetGlobalName`
+///
+/// Operation:
+///  - TODO: doc
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct GetGlobalName;
+
+impl GetGlobalName {
+    fn operation(context: &mut Context<'_>, index: usize) -> JsResult<CompletionType> {
+        let key = context.vm.frame().code_block().names[index].clone();
+        let global = context.global_object();
+        if !global.has_property(key.clone(), context)? {
+            return Err(JsNativeError::reference()
+                .with_message(format!("{} is not defined", key.to_std_string_escaped()))
+                .into());
+        }
+
+        let value = global.get(key, context)?;
+        context.vm.push(value);
+        Ok(CompletionType::Normal)
+    }
+}
+
+impl Operation for GetGlobalName {
+    const NAME: &'static str = "GetGlobalName";
+    const INSTRUCTION: &'static str = "INST - GetGlobalName";
+
+    fn execute(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let index = context.vm.read::<u8>() as usize;
+        Self::operation(context, index)
+    }
+
+    fn execute_with_u16_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let index = context.vm.read::<u16>() as usize;
+        Self::operation(context, index)
+    }
+
+    fn execute_with_u32_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let index = context.vm.read::<u32>() as usize;
+        Self::operation(context, index)
+    }
+}
+
+/// `GetGlobalNameOrUndefined` implements the Opcode Operation for `Opcode::GetGlobalNameOrUndefined`
+///
+/// Operation:
+///  - TODO: doc
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct GetGlobalNameOrUndefined;
+
+impl GetGlobalNameOrUndefined {
+    fn operation(context: &mut Context<'_>, index: usize) -> JsResult<CompletionType> {
+        let key = context.vm.frame().code_block().names[index].clone();
+        let global = context.global_object();
+        if !global.has_property(key.clone(), context)? {
+            context.vm.push(JsValue::undefined());
+            return Ok(CompletionType::Normal);
+        }
+
+        let value = global.get(key, context)?;
+        context.vm.push(value);
+        Ok(CompletionType::Normal)
+    }
+}
+
+impl Operation for GetGlobalNameOrUndefined {
+    const NAME: &'static str = "GetGlobalNameOrUndefined";
+    const INSTRUCTION: &'static str = "INST - GetGlobalNameOrUndefined";
+
+    fn execute(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let index = context.vm.read::<u8>() as usize;
+        Self::operation(context, index)
+    }
+
+    fn execute_with_u16_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let index = context.vm.read::<u16>() as usize;
+        Self::operation(context, index)
+    }
+
+    fn execute_with_u32_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let index = context.vm.read::<u32>() as usize;
+        Self::operation(context, index)
     }
 }
 
diff --git a/boa_engine/src/vm/opcode/mod.rs b/boa_engine/src/vm/opcode/mod.rs
index c7279be5fb1..52b48579af6 100644
--- a/boa_engine/src/vm/opcode/mod.rs
+++ b/boa_engine/src/vm/opcode/mod.rs
@@ -2036,6 +2036,48 @@ generate_opcodes! {
     /// Stack: **=>**
     PopPrivateEnvironment,
 
+    /// Delete global variable.
+    ///
+    /// Operands: index: `VaryingOperand`
+    ///
+    /// Stack: **=>**
+    DeleteGlobalName { index: VaryingOperand },
+
+    /// Get global variable.
+    ///
+    /// Operands: index: `VaryingOperand`
+    ///
+    /// Stack: **=>** value
+    GetGlobalName { index: VaryingOperand },
+
+    /// Get global variable or undefined if it does not exist.
+    ///
+    /// Operands: index: `VaryingOperand`
+    ///
+    /// Stack: **=>** value
+    GetGlobalNameOrUndefined { index: VaryingOperand },
+
+    /// Set global variable.
+    ///
+    /// Operands: index: `VaryingOperand`
+    ///
+    /// Stack: value **=>**
+    SetGlobalName { index: VaryingOperand },
+
+    /// Get fast local variable.
+    ///
+    /// Operands: index: `VaryingOperand`
+    ///
+    /// Stack: **=>** value
+    GetLocal { index: VaryingOperand },
+
+    /// Get fast local variable.
+    ///
+    /// Operands: index: `VaryingOperand`
+    ///
+    /// Stack: value **=>**
+    SetLocal { index: VaryingOperand },
+
     /// No-operation instruction, does nothing.
     ///
     /// Operands:
@@ -2161,18 +2203,6 @@ generate_opcodes! {
     Reserved51 => Reserved,
     /// Reserved [`Opcode`].
     Reserved52 => Reserved,
-    /// Reserved [`Opcode`].
-    Reserved53 => Reserved,
-    /// Reserved [`Opcode`].
-    Reserved54 => Reserved,
-    /// Reserved [`Opcode`].
-    Reserved55 => Reserved,
-    /// Reserved [`Opcode`].
-    Reserved56 => Reserved,
-    /// Reserved [`Opcode`].
-    Reserved57 => Reserved,
-    /// Reserved [`Opcode`].
-    Reserved58 => Reserved,
 }
 
 /// Specific opcodes for bindings.
diff --git a/boa_engine/src/vm/opcode/set/name.rs b/boa_engine/src/vm/opcode/set/name.rs
index d292d56bbd8..e8b5cc3f7f0 100644
--- a/boa_engine/src/vm/opcode/set/name.rs
+++ b/boa_engine/src/vm/opcode/set/name.rs
@@ -29,8 +29,8 @@ impl Operation for ThrowMutateImmutable {
     const INSTRUCTION: &'static str = "INST - ThrowMutateImmutable";
 
     fn execute(context: &mut Context<'_>) -> JsResult<CompletionType> {
-        let index = context.vm.read::<u8>();
-        Self::operation(context, index as usize)
+        let index = context.vm.read::<u8>() as usize;
+        Self::operation(context, index)
     }
 
     fn execute_with_u16_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
@@ -39,8 +39,59 @@ impl Operation for ThrowMutateImmutable {
     }
 
     fn execute_with_u32_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
-        let index = context.vm.read::<u32>();
-        Self::operation(context, index as usize)
+        let index = context.vm.read::<u32>() as usize;
+        Self::operation(context, index)
+    }
+}
+
+/// `SetGlobalName` implements the Opcode Operation for `Opcode::SetGlobalName`
+///
+/// Operation:
+///  - Set global name.
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct SetGlobalName;
+
+impl SetGlobalName {
+    fn operation(context: &mut Context<'_>, index: usize) -> JsResult<CompletionType> {
+        let value = context.vm.pop();
+
+        let strict = context.vm.frame().code_block.strict();
+        let key = context.vm.frame().code_block().names[index].clone();
+
+        let global = context.global_object();
+        let has_property = global.has_property(key.clone(), context)?;
+        if !has_property && strict {
+            return Err(JsNativeError::reference()
+                .with_message(format!(
+                    "cannot assign to uninitialized global property `{}`",
+                    key.to_std_string_escaped()
+                ))
+                .into());
+        }
+
+        global.set(key, value, strict, context)?;
+
+        Ok(CompletionType::Normal)
+    }
+}
+
+impl Operation for SetGlobalName {
+    const NAME: &'static str = "SetGlobalName";
+    const INSTRUCTION: &'static str = "INST - SetGlobalName";
+
+    fn execute(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let index = context.vm.read::<u8>() as usize;
+        Self::operation(context, index)
+    }
+
+    fn execute_with_u16_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let index = context.vm.read::<u16>() as usize;
+        Self::operation(context, index)
+    }
+
+    fn execute_with_u32_operands(context: &mut Context<'_>) -> JsResult<CompletionType> {
+        let index = context.vm.read::<u32>() as usize;
+        Self::operation(context, index)
     }
 }