From 5ec468bfdd234e5c0c5b8804fdfb76915c9c9ec8 Mon Sep 17 00:00:00 2001
From: Tim Ledbetter <tim.ledbetter@ladybird.org>
Date: Fri, 19 Jun 2026 15:07:27 +0100
Subject: [PATCH] LibJS: Store module indirect bindings in a HashMap

Previously, these were stored in a vector that was linearly scanned.
For large sites this vector could contain hundreds of entries, so
a HashMap gives a significant speedup.
---
 Libraries/LibJS/Runtime/ModuleEnvironment.cpp | 18 +++++++-----------
 Libraries/LibJS/Runtime/ModuleEnvironment.h   |  5 ++---
 2 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/Libraries/LibJS/Runtime/ModuleEnvironment.cpp b/Libraries/LibJS/Runtime/ModuleEnvironment.cpp
index 33b63eb2d2..37f21c0b1e 100644
--- a/Libraries/LibJS/Runtime/ModuleEnvironment.cpp
+++ b/Libraries/LibJS/Runtime/ModuleEnvironment.cpp
@@ -74,10 +74,8 @@ ThrowCompletionOr<void> ModuleEnvironment::create_import_binding(Utf16FlyString
     // FIXME: I don't know what this means or how to check it.
 
     // 3. Create an immutable indirect binding in envRec for N that references M and N2 as its target binding and record that the binding is initialized.
-    // Note: We use the fact that the binding is in this list as it being initialized.
-    m_indirect_bindings.append({ move(name),
-        module,
-        move(binding_name) });
+    // Note: We use the fact that the binding is in this map as it being initialized.
+    m_indirect_bindings.set(move(name), IndirectBinding { module, move(binding_name) });
 
     // 4. Return unused.
     return {};
@@ -85,13 +83,11 @@ ThrowCompletionOr<void> ModuleEnvironment::create_import_binding(Utf16FlyString
 
 ModuleEnvironment::IndirectBinding const* ModuleEnvironment::get_indirect_binding(Utf16FlyString const& name) const
 {
-    auto binding_or_end = m_indirect_bindings.find_if([&](IndirectBinding const& binding) {
-        return binding.name == name;
-    });
-    if (binding_or_end.is_end())
+    auto it = m_indirect_bindings.find(name);
+    if (it == m_indirect_bindings.end())
         return nullptr;
 
-    return &(*binding_or_end);
+    return &it->value;
 }
 
 Optional<ModuleEnvironment::BindingAndIndex> ModuleEnvironment::find_binding_and_index(Utf16FlyString const& name) const
@@ -131,14 +127,14 @@ Optional<ModuleEnvironment::BindingAndIndex> ModuleEnvironment::find_binding_and
 size_t ModuleEnvironment::external_memory_size() const
 {
     auto size = DeclarativeEnvironment::external_memory_size();
-    size = saturating_add_external_memory_size(size, vector_external_memory_size(m_indirect_bindings));
+    size = saturating_add_external_memory_size(size, hash_map_external_memory_size(m_indirect_bindings));
     return size;
 }
 
 void ModuleEnvironment::visit_edges(Visitor& visitor)
 {
     Base::visit_edges(visitor);
-    for (auto& indirect_binding : m_indirect_bindings)
+    for (auto& [_, indirect_binding] : m_indirect_bindings)
         visitor.visit(indirect_binding.module);
 }
 
diff --git a/Libraries/LibJS/Runtime/ModuleEnvironment.h b/Libraries/LibJS/Runtime/ModuleEnvironment.h
index bdbc29c7ce..6102ac0e6e 100644
--- a/Libraries/LibJS/Runtime/ModuleEnvironment.h
+++ b/Libraries/LibJS/Runtime/ModuleEnvironment.h
@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <AK/HashMap.h>
 #include <LibJS/Module.h>
 #include <LibJS/Runtime/DeclarativeEnvironment.h>
 #include <LibJS/Runtime/Environment.h>
@@ -35,7 +36,6 @@ private:
     virtual size_t external_memory_size() const override;
 
     struct IndirectBinding {
-        Utf16FlyString name;
         GC::Ptr<Module> module;
         Utf16FlyString binding_name;
     };
@@ -43,8 +43,7 @@ private:
 
     virtual Optional<BindingAndIndex> find_binding_and_index(Utf16FlyString const& name) const override;
 
-    // FIXME: Since we always access this via the name this could be a map.
-    Vector<IndirectBinding> m_indirect_bindings;
+    HashMap<Utf16FlyString, IndirectBinding> m_indirect_bindings;
 };
 
 }