From 412467cc70d66c02a9c6de44da019273ddb544a5 Mon Sep 17 00:00:00 2001
From: Zaggy1024 <Zaggy1024@gmail.com>
Date: Thu, 9 Oct 2025 16:58:17 -0500
Subject: [PATCH] LibWeb: Add a hook in EventLoop to call a task when reaching
 step 1

---
 Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp | 13 +++++++++++++
 Libraries/LibWeb/HTML/EventLoop/EventLoop.h   |  5 +++++
 2 files changed, 18 insertions(+)

diff --git a/Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp b/Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp
index 8801d05aed..73d00503ae 100644
--- a/Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp
+++ b/Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp
@@ -49,6 +49,7 @@ EventLoop::~EventLoop() = default;
 void EventLoop::visit_edges(Visitor& visitor)
 {
     Base::visit_edges(visitor);
+    visitor.visit(m_reached_step_1_tasks);
     visitor.visit(m_task_queue);
     visitor.visit(m_microtask_queue);
     visitor.visit(m_currently_running_task);
@@ -163,6 +164,12 @@ void EventLoop::process()
     GC::Ptr<Task> oldest_task;
     [[maybe_unused]] double task_start_time = 0;
 
+    // Some algorithms request that steps or states only occur once the event loop has reached step 1.
+    // Invoke a set of tasks that these algorithms request us to in order to achieve this.
+    auto reached_step_1_tasks = move(m_reached_step_1_tasks);
+    for (auto& reached_step_1_task : reached_step_1_tasks)
+        reached_step_1_task->function()();
+
     // 2. If the event loop has a task queue with at least one runnable task, then:
     if (m_task_queue->has_runnable_tasks()) {
         // 1. Let taskQueue be one such task queue, chosen in an implementation-defined manner.
@@ -508,6 +515,12 @@ void EventLoop::update_the_rendering()
     }
 }
 
+void run_when_event_loop_reaches_step_1(GC::Ref<GC::Function<void()>> steps)
+{
+    auto& event_loop = main_thread_event_loop();
+    event_loop.run_upon_reaching_step_1(steps);
+}
+
 // https://html.spec.whatwg.org/multipage/webappapis.html#queue-a-task
 TaskID queue_a_task(HTML::Task::Source source, GC::Ptr<EventLoop> event_loop, GC::Ptr<DOM::Document> document, GC::Ref<GC::Function<void()>> steps)
 {
diff --git a/Libraries/LibWeb/HTML/EventLoop/EventLoop.h b/Libraries/LibWeb/HTML/EventLoop/EventLoop.h
index 5d41e7ecda..9de3237f44 100644
--- a/Libraries/LibWeb/HTML/EventLoop/EventLoop.h
+++ b/Libraries/LibWeb/HTML/EventLoop/EventLoop.h
@@ -48,6 +48,8 @@ public:
 
     Type type() const { return m_type; }
 
+    void run_upon_reaching_step_1(GC::Ref<GC::Function<void()>> task) { m_reached_step_1_tasks.append(task); }
+
     TaskQueue& task_queue() { return *m_task_queue; }
     TaskQueue const& task_queue() const { return *m_task_queue; }
 
@@ -103,6 +105,8 @@ private:
 
     Type m_type { Type::Window };
 
+    Vector<GC::Ref<GC::Function<void()>>> m_reached_step_1_tasks;
+
     GC::Ptr<TaskQueue> m_task_queue;
     GC::Ptr<TaskQueue> m_microtask_queue;
 
@@ -142,6 +146,7 @@ private:
 };
 
 WEB_API EventLoop& main_thread_event_loop();
+WEB_API void run_when_event_loop_reaches_step_1(GC::Ref<GC::Function<void()>> steps);
 WEB_API TaskID queue_a_task(HTML::Task::Source, GC::Ptr<EventLoop>, GC::Ptr<DOM::Document>, GC::Ref<GC::Function<void()>> steps);
 WEB_API TaskID queue_global_task(HTML::Task::Source, JS::Object&, GC::Ref<GC::Function<void()>> steps);
 WEB_API void queue_a_microtask(DOM::Document const*, GC::Ref<GC::Function<void()>> steps);