script/dom/event/

eventtarget.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

use std::cell::{RefCell, RefMut};
use std::collections::hash_map::Entry::{Occupied, Vacant};
use std::default::Default;
use std::ffi::CString;
use std::mem;
use std::ops::{Deref, DerefMut};
use std::rc::Rc;
use std::sync::LazyLock;

use deny_public_fields::DenyPublicFields;
use devtools_traits::EventListenerInfo;
use dom_struct::dom_struct;
use js::context::JSContext;
use js::jsapi::{JS_GetFunctionObject, SupportUnscopables};
use js::jsval::JSVal;
use js::rust::wrappers2::CompileFunction;
use js::rust::{CompileOptionsWrapper, HandleObject, transform_u16_to_source_text};
use libc::c_char;
use rustc_hash::{FxBuildHasher, FxHashSet};
use script_bindings::callback::OwnerWindow;
use script_bindings::cell::DomRefCell;
use script_bindings::cformat;
use script_bindings::reflector::{DomObject, Reflector, reflect_dom_object_with_proto};
use servo_constellation_traits::ConstellationInterest;
use servo_url::ServoUrl;
use style::str::HTML_SPACE_CHARACTERS;
use stylo_atoms::Atom;

use crate::conversions::Convert;
use crate::dom::abortsignal::{AbortAlgorithm, RemovableDomEventListener};
use crate::dom::beforeunloadevent::BeforeUnloadEvent;
use crate::dom::bindings::callback::{CallbackContainer, CallbackFunction, ExceptionHandling};
use crate::dom::bindings::codegen::Bindings::BeforeUnloadEventBinding::BeforeUnloadEventMethods;
use crate::dom::bindings::codegen::Bindings::ErrorEventBinding::ErrorEventMethods;
use crate::dom::bindings::codegen::Bindings::EventBinding::EventMethods;
use crate::dom::bindings::codegen::Bindings::EventHandlerBinding::{
    EventHandlerNonNull, OnBeforeUnloadEventHandlerNonNull, OnErrorEventHandlerNonNull,
};
use crate::dom::bindings::codegen::Bindings::EventListenerBinding::EventListener;
use crate::dom::bindings::codegen::Bindings::EventTargetBinding::{
    AddEventListenerOptions, EventListenerOptions, EventTargetMethods,
};
use crate::dom::bindings::codegen::Bindings::NodeBinding::GetRootNodeOptions;
use crate::dom::bindings::codegen::Bindings::NodeBinding::Node_Binding::NodeMethods;
use crate::dom::bindings::codegen::Bindings::ShadowRootBinding::ShadowRoot_Binding::ShadowRootMethods;
use crate::dom::bindings::codegen::Bindings::WindowBinding::WindowMethods;
use crate::dom::bindings::codegen::GenericBindings::DocumentBinding::Document_Binding::DocumentMethods;
use crate::dom::bindings::codegen::UnionTypes::{
    AddEventListenerOptionsOrBoolean, EventListenerOptionsOrBoolean, EventOrString,
};
use crate::dom::bindings::error::{Error, Fallible, report_pending_exception};
use crate::dom::bindings::inheritance::Castable;
use crate::dom::bindings::reflector::DomGlobal;
use crate::dom::bindings::root::{Dom, DomRoot};
use crate::dom::bindings::str::DOMString;
use crate::dom::bindings::trace::HashMapTracedValues;
use crate::dom::csp::{CspReporting, InlineCheckType};
use crate::dom::document::Document;
use crate::dom::element::Element;
use crate::dom::errorevent::ErrorEvent;
use crate::dom::event::{Event, EventBubbles, EventCancelable, EventComposed};
use crate::dom::globalscope::GlobalScope;
use crate::dom::html::htmlformelement::FormControlElementHelpers;
use crate::dom::indexeddb::idbdatabase::IDBDatabase;
use crate::dom::indexeddb::idbrequest::IDBRequest;
use crate::dom::indexeddb::idbtransaction::IDBTransaction;
use crate::dom::node::virtualmethods::VirtualMethods;
use crate::dom::node::{Node, NodeTraits};
use crate::dom::shadowroot::ShadowRoot;
use crate::dom::window::Window;
use crate::dom::workerglobalscope::WorkerGlobalScope;
use crate::realms::enter_auto_realm;
use crate::runtime::script_runtime::IntroductionType;

/// <https://html.spec.whatwg.org/multipage/#event-handler-content-attributes>
/// Generated from WebIDL definitions of EventHandler attributes on interfaces
/// that inherit from Node.
pub(crate) static CONTENT_EVENT_HANDLER_NAMES: LazyLock<FxHashSet<&str>> = LazyLock::new(|| {
    FxHashSet::from_iter(include!(concat!(
        env!("OUT_DIR"),
        "/ContentEventHandlerNames.rs"
    )))
});

#[derive(Clone, JSTraceable, MallocSizeOf, PartialEq)]
#[expect(clippy::enum_variant_names)]
pub(crate) enum CommonEventHandler {
    EventHandler(#[conditional_malloc_size_of] Rc<EventHandlerNonNull>),

    ErrorEventHandler(#[conditional_malloc_size_of] Rc<OnErrorEventHandlerNonNull>),

    BeforeUnloadEventHandler(#[conditional_malloc_size_of] Rc<OnBeforeUnloadEventHandlerNonNull>),
}

impl CommonEventHandler {
    fn parent(&self) -> &CallbackFunction<crate::DomTypeHolder> {
        match *self {
            CommonEventHandler::EventHandler(ref handler) => &handler.parent,
            CommonEventHandler::ErrorEventHandler(ref handler) => &handler.parent,
            CommonEventHandler::BeforeUnloadEventHandler(ref handler) => &handler.parent,
        }
    }
}

#[derive(Clone, Copy, Debug, JSTraceable, MallocSizeOf, PartialEq)]
pub(crate) enum ListenerPhase {
    Capturing,
    Bubbling,
}

/// <https://html.spec.whatwg.org/multipage/#internal-raw-uncompiled-handler>
#[derive(Clone, JSTraceable, MallocSizeOf, PartialEq)]
struct InternalRawUncompiledHandler {
    source: DOMString,
    #[no_trace]
    url: ServoUrl,
    line: usize,
}

/// A representation of an event handler, either compiled or uncompiled raw source, or null.
#[derive(Clone, JSTraceable, MallocSizeOf, PartialEq)]
enum InlineEventListener {
    Uncompiled(InternalRawUncompiledHandler),
    Compiled(CommonEventHandler),
    Null,
}

/// Get a compiled representation of this event handler, compiling it from its
/// raw source if necessary.
/// <https://html.spec.whatwg.org/multipage/#getting-the-current-value-of-the-event-handler>
fn get_compiled_handler(
    cx: &mut JSContext,
    inline_listener: &RefCell<InlineEventListener>,
    owner: &EventTarget,
    ty: &Atom,
) -> Option<CommonEventHandler> {
    let listener = mem::replace(
        &mut *inline_listener.borrow_mut(),
        InlineEventListener::Null,
    );
    let compiled = match listener {
        InlineEventListener::Null => None,
        InlineEventListener::Uncompiled(handler) => {
            owner.get_compiled_event_handler(cx, handler, ty)
        },
        InlineEventListener::Compiled(handler) => Some(handler),
    };
    if let Some(ref compiled) = compiled {
        *inline_listener.borrow_mut() = InlineEventListener::Compiled(compiled.clone());
    }
    compiled
}

#[derive(Clone, JSTraceable, MallocSizeOf, PartialEq)]
enum EventListenerType {
    Additive(#[conditional_malloc_size_of] Rc<EventListener>),
    Inline(RefCell<InlineEventListener>),
}

impl EventListenerType {
    fn get_compiled_listener(
        &self,
        cx: &mut JSContext,
        owner: &EventTarget,
        ty: &Atom,
    ) -> Option<CompiledEventListener> {
        match *self {
            EventListenerType::Inline(ref inline) => {
                get_compiled_handler(cx, inline, owner, ty).map(CompiledEventListener::Handler)
            },
            EventListenerType::Additive(ref listener) => {
                Some(CompiledEventListener::Listener(listener.clone()))
            },
        }
    }
}

/// A representation of an EventListener/EventHandler object that has previously
/// been compiled successfully, if applicable.
pub(crate) enum CompiledEventListener {
    Listener(Rc<EventListener>),
    Handler(CommonEventHandler),
}

impl CompiledEventListener {
    #[expect(unsafe_code)]
    pub(crate) fn associated_global(&self) -> DomRoot<GlobalScope> {
        let obj = match self {
            CompiledEventListener::Listener(listener) => listener.callback(),
            CompiledEventListener::Handler(CommonEventHandler::EventHandler(handler)) => {
                handler.callback()
            },
            CompiledEventListener::Handler(CommonEventHandler::ErrorEventHandler(handler)) => {
                handler.callback()
            },
            CompiledEventListener::Handler(CommonEventHandler::BeforeUnloadEventHandler(
                handler,
            )) => handler.callback(),
        };
        unsafe { GlobalScope::from_object(obj) }
    }

    // https://html.spec.whatwg.org/multipage/#the-event-handler-processing-algorithm
    pub(crate) fn call_or_handle_event(
        &self,
        cx: &mut JSContext,
        object: &EventTarget,
        event: &Event,
        exception_handle: ExceptionHandling,
    ) -> Fallible<()> {
        // Step 3
        match *self {
            CompiledEventListener::Listener(ref listener) => {
                listener.HandleEvent_(cx, object, event, exception_handle)
            },
            CompiledEventListener::Handler(ref handler) => {
                match *handler {
                    CommonEventHandler::ErrorEventHandler(ref handler) => {
                        if let Some(event) = event.downcast::<ErrorEvent>() &&
                            (object.is::<Window>() || object.is::<WorkerGlobalScope>())
                        {
                            rooted!(&in(cx) let mut error: JSVal);
                            event.Error(error.handle_mut());
                            rooted!(&in(cx) let mut rooted_return_value: JSVal);
                            let return_value = handler.Call_(
                                cx,
                                object,
                                EventOrString::String(event.Message()),
                                Some(event.Filename()),
                                Some(event.Lineno()),
                                Some(event.Colno()),
                                Some(error.handle()),
                                rooted_return_value.handle_mut(),
                                exception_handle,
                            );
                            // Step 4
                            if let Ok(()) = return_value &&
                                rooted_return_value.handle().is_boolean() &&
                                rooted_return_value.handle().to_boolean()
                            {
                                event.upcast::<Event>().PreventDefault();
                            }
                            return return_value;
                        }

                        rooted!(&in(cx) let mut rooted_return_value: JSVal);
                        handler.Call_(
                            cx,
                            object,
                            EventOrString::Event(DomRoot::from_ref(event)),
                            None,
                            None,
                            None,
                            None,
                            rooted_return_value.handle_mut(),
                            exception_handle,
                        )
                    },

                    CommonEventHandler::BeforeUnloadEventHandler(ref handler) => {
                        if let Some(event) = event.downcast::<BeforeUnloadEvent>() {
                            // Step 5
                            match handler.Call_(
                                cx,
                                object,
                                event.upcast::<Event>(),
                                exception_handle,
                            ) {
                                Ok(value) => {
                                    let rv = event.ReturnValue();
                                    if let Some(v) = value {
                                        if rv.is_empty() {
                                            event.SetReturnValue(v);
                                        }
                                        event.upcast::<Event>().PreventDefault();
                                    }
                                    Ok(())
                                },
                                Err(err) => Err(err),
                            }
                        } else {
                            // Step 5, "Otherwise" clause
                            handler
                                .Call_(cx, object, event.upcast::<Event>(), exception_handle)
                                .map(|_| ())
                        }
                    },

                    CommonEventHandler::EventHandler(ref handler) => {
                        rooted!(&in(cx) let mut rooted_return_value: JSVal);
                        match handler.Call_(
                            cx,
                            object,
                            event,
                            rooted_return_value.handle_mut(),
                            exception_handle,
                        ) {
                            Ok(()) => {
                                let value = rooted_return_value.handle();

                                // Step 5
                                let should_cancel = value.is_boolean() && !value.to_boolean();

                                if should_cancel {
                                    // FIXME: spec says to set the cancelled flag directly
                                    // here, not just to prevent default;
                                    // can that ever make a difference?
                                    event.PreventDefault();
                                }
                                Ok(())
                            },
                            Err(err) => Err(err),
                        }
                    },
                }
            },
        }
    }
}

// https://dom.spec.whatwg.org/#concept-event-listener
// (as distinct from https://dom.spec.whatwg.org/#callbackdef-eventlistener)
#[derive(Clone, DenyPublicFields, JSTraceable, MallocSizeOf)]
/// A listener in a collection of event listeners.
pub(crate) struct EventListenerEntry {
    phase: ListenerPhase,
    listener: EventListenerType,
    once: bool,
    passive: bool,
    removed: bool,
}

impl EventListenerEntry {
    pub(crate) fn phase(&self) -> ListenerPhase {
        self.phase
    }

    pub(crate) fn once(&self) -> bool {
        self.once
    }

    pub(crate) fn removed(&self) -> bool {
        self.removed
    }

    /// <https://html.spec.whatwg.org/multipage/#getting-the-current-value-of-the-event-handler>
    pub(crate) fn get_compiled_listener(
        &self,
        cx: &mut JSContext,
        owner: &EventTarget,
        ty: &Atom,
    ) -> Option<CompiledEventListener> {
        self.listener.get_compiled_listener(cx, owner, ty)
    }
}

impl std::cmp::PartialEq for EventListenerEntry {
    fn eq(&self, other: &Self) -> bool {
        self.phase == other.phase && self.listener == other.listener
    }
}

#[derive(Clone, JSTraceable, MallocSizeOf)]
/// A mix of potentially uncompiled and compiled event listeners of the same type.
pub(crate) struct EventListeners(
    #[conditional_malloc_size_of] Vec<Rc<RefCell<EventListenerEntry>>>,
);

impl Deref for EventListeners {
    type Target = Vec<Rc<RefCell<EventListenerEntry>>>;
    fn deref(&self) -> &Vec<Rc<RefCell<EventListenerEntry>>> {
        &self.0
    }
}

impl DerefMut for EventListeners {
    fn deref_mut(&mut self) -> &mut Vec<Rc<RefCell<EventListenerEntry>>> {
        &mut self.0
    }
}

impl EventListeners {
    /// <https://html.spec.whatwg.org/multipage/#getting-the-current-value-of-the-event-handler>
    fn get_inline_listener(
        &self,
        cx: &mut JSContext,
        owner: &EventTarget,
        ty: &Atom,
    ) -> Option<CommonEventHandler> {
        for entry in &self.0 {
            if let EventListenerType::Inline(ref inline) = entry.borrow().listener {
                // Step 1.1-1.8 and Step 2
                return get_compiled_handler(cx, inline, owner, ty);
            }
        }

        // Step 2
        None
    }

    fn has_listeners(&self) -> bool {
        !self.0.is_empty()
    }
}

/// The set of event listeners registered on an [`EventTarget`], keyed by event type.
type EventListenerMap = HashMapTracedValues<Atom, EventListeners, FxBuildHasher>;

#[dom_struct]
pub struct EventTarget {
    reflector_: Reflector,
    handlers: DomRefCell<Option<Box<EventListenerMap>>>,
}

impl EventTarget {
    pub(crate) fn new_inherited() -> EventTarget {
        EventTarget {
            reflector_: Reflector::new(),
            handlers: DomRefCell::new(None),
        }
    }

    /// Mutably borrow the listener map, allocating it if this target has none yet.
    fn ensure_handlers(&self) -> RefMut<'_, Box<EventListenerMap>> {
        RefMut::map(self.handlers.borrow_mut(), |handlers| {
            handlers.get_or_insert_with(Box::default)
        })
    }

    fn new(
        cx: &mut JSContext,
        global: &GlobalScope,
        proto: Option<HandleObject>,
    ) -> DomRoot<EventTarget> {
        reflect_dom_object_with_proto(cx, Box::new(EventTarget::new_inherited()), global, proto)
    }

    /// Returns the [`ConstellationInterest`] associated with a given event type
    /// on this specific target, if any. The mapping depends on the concrete type
    /// of the EventTarget since the same event name can be used in multiple contexts.
    fn interest_for_event_type(&self, ty: &Atom) -> Option<ConstellationInterest> {
        if self.is::<Window>() && *ty == atom!("storage") {
            return Some(ConstellationInterest::StorageEvent);
        }
        None
    }

    /// Notify the global about a listener being added for a given event type.
    fn notify_listener_added(&self, ty: &Atom) {
        if let Some(interest) = self.interest_for_event_type(ty) {
            self.global().register_interest(interest);
        }
    }

    /// Notify the global about a listener being removed for a given event type.
    fn notify_listener_removed(&self, ty: &Atom) {
        if let Some(interest) = self.interest_for_event_type(ty) {
            self.global().unregister_interest(interest);
        }
    }

    /// Determine if there are any listeners for a given event type.
    /// See <https://github.com/whatwg/dom/issues/453>.
    pub(crate) fn has_listeners_for(&self, type_: &Atom) -> bool {
        match self
            .handlers
            .borrow()
            .as_ref()
            .and_then(|handlers| handlers.get(type_))
        {
            Some(listeners) => listeners.has_listeners(),
            None => false,
        }
    }

    pub(crate) fn get_listeners_for(&self, type_: &Atom) -> EventListeners {
        self.handlers
            .borrow()
            .as_ref()
            .and_then(|handlers| handlers.get(type_))
            .map_or(EventListeners(vec![]), |listeners| listeners.clone())
    }

    pub(crate) fn remove_all_listeners(&self) {
        // Take the whole map out first, so the listener-removed notifications
        // below run without holding a borrow on `handlers`.
        let Some(handlers) = self.handlers.borrow_mut().take() else {
            return;
        };

        for (ty, entries) in handlers.iter() {
            entries
                .iter()
                .for_each(|entry| entry.borrow_mut().removed = true);
            self.notify_listener_removed(ty);
        }
    }

    /// <https://dom.spec.whatwg.org/#default-passive-value>
    fn default_passive_value(&self, ty: &Atom) -> bool {
        // Return true if all of the following are true:
        let event_type = ty.trim_matches(HTML_SPACE_CHARACTERS);

        // type is one of "touchstart", "touchmove", "wheel", or "mousewheel"
        let matches_event_type = event_type.eq_ignore_ascii_case("touchstart") ||
            event_type.eq_ignore_ascii_case("touchmove") ||
            event_type.eq_ignore_ascii_case("wheel") ||
            event_type.eq_ignore_ascii_case("mousewheel");

        if !matches_event_type {
            return false;
        }

        // eventTarget is a Window object
        if self.is::<Window>() {
            return true;
        }

        // or ...
        if let Some(node) = self.downcast::<Node>() {
            let node_document = node.owner_document();
            let event_target = self.upcast::<EventTarget>();

            // is a node whose node document is eventTarget
            return event_target == node_document.upcast::<EventTarget>()
                // or is a node whose node document’s document element is eventTarget
                || node_document.GetDocumentElement().is_some_and(|n| n.upcast::<EventTarget>() == event_target)
                // or is a node whose node document’s body element is eventTarget
                || node_document.GetBody().is_some_and(|n| n.upcast::<EventTarget>() == event_target);
        }

        false
    }

    /// <https://html.spec.whatwg.org/multipage/#event-handler-attributes:event-handlers-11>
    fn set_inline_event_listener(&self, ty: Atom, listener: Option<InlineEventListener>) {
        let mut handlers = self.ensure_handlers();
        let entries = match handlers.entry(ty.clone()) {
            Occupied(entry) => entry.into_mut(),
            Vacant(entry) => entry.insert(EventListeners(vec![])),
        };

        let idx = entries
            .iter()
            .position(|entry| matches!(entry.borrow().listener, EventListenerType::Inline(_)));

        match idx {
            Some(idx) => match listener {
                // Replace if there's something to replace with,
                // but remove entirely if there isn't.
                Some(listener) => {
                    entries[idx].borrow_mut().listener = EventListenerType::Inline(listener.into());
                },
                None => {
                    entries.remove(idx).borrow_mut().removed = true;
                    self.notify_listener_removed(&ty);
                },
            },
            None => {
                if let Some(listener) = listener {
                    entries.push(Rc::new(RefCell::new(EventListenerEntry {
                        phase: ListenerPhase::Bubbling,
                        listener: EventListenerType::Inline(listener.into()),
                        once: false,
                        passive: self.default_passive_value(&ty),
                        removed: false,
                    })));
                    self.notify_listener_added(&ty)
                }
            },
        }
    }

    pub(crate) fn remove_listener(&self, ty: &Atom, entry: &Rc<RefCell<EventListenerEntry>>) {
        let mut handlers = self.handlers.borrow_mut();

        if let Some(handlers) = handlers.as_mut() &&
            let Some(entries) = handlers.get_mut(ty) &&
            let Some(position) = entries.iter().position(|e| *e == *entry)
        {
            entries.remove(position).borrow_mut().removed = true;
            self.notify_listener_removed(ty);
        }
    }

    /// Determines the `passive` attribute of an associated event listener
    pub(crate) fn is_passive(&self, listener: &Rc<RefCell<EventListenerEntry>>) -> bool {
        listener.borrow().passive
    }

    /// Determines if there are any non-passive listeners for a given event type.
    pub(crate) fn has_non_passive_listener(&self, type_: &Atom) -> bool {
        self.get_listeners_for(type_)
            .iter()
            .any(|listener| !self.is_passive(listener))
    }

    fn get_inline_event_listener(
        &self,
        cx: &mut JSContext,
        ty: &Atom,
    ) -> Option<CommonEventHandler> {
        let handlers = self.handlers.borrow();
        handlers
            .as_ref()?
            .get(ty)
            .and_then(|entry| entry.get_inline_listener(cx, self, ty))
    }

    /// Store the raw uncompiled event handler for on-demand compilation later.
    /// <https://html.spec.whatwg.org/multipage/#event-handler-attributes:event-handler-content-attributes-3>
    pub(crate) fn set_event_handler_uncompiled(
        &self,
        cx: &mut JSContext,
        url: ServoUrl,
        line: usize,
        ty: &str,
        source: &str,
    ) {
        if let Some(element) = self.downcast::<Element>() {
            let doc = element.owner_document();
            let global = &doc.global();
            if global
                .get_csp_list()
                .should_elements_inline_type_behavior_be_blocked(
                    cx,
                    global,
                    element.upcast(),
                    InlineCheckType::ScriptAttribute,
                    source,
                    line as u32,
                )
            {
                return;
            }
        };

        let handler = InternalRawUncompiledHandler {
            source: DOMString::from(source),
            line,
            url,
        };
        self.set_inline_event_listener(
            Atom::from(ty),
            Some(InlineEventListener::Uncompiled(handler)),
        );
    }

    // https://html.spec.whatwg.org/multipage/#getting-the-current-value-of-the-event-handler
    // step 3
    #[expect(unsafe_code)]
    fn get_compiled_event_handler(
        &self,
        cx: &mut JSContext,
        handler: InternalRawUncompiledHandler,
        ty: &Atom,
    ) -> Option<CommonEventHandler> {
        // Step 3.1
        let element = self.downcast::<Element>();
        let document = match element {
            Some(element) => element.owner_document(),
            None => self.downcast::<Window>().unwrap().Document(),
        };

        // Step 3.2
        if !document.scripting_enabled() {
            return None;
        }

        // Step 3.3
        let body: Vec<u16> = handler.source.str().encode_utf16().collect();

        // Step 3.4 is handler.line

        // Step 3.5
        let form_owner = element
            .and_then(|e| e.as_maybe_form_control())
            .and_then(|f| f.form_owner());

        // Step 3.6 TODO: settings objects not implemented

        // Step 3.7 is written as though we call the parser separately
        // from the compiler; since we just call CompileFunction with
        // source text, we handle parse errors later

        // Step 3.8 TODO: settings objects not implemented
        let window = document.window();
        let mut realm = enter_auto_realm(cx, window);
        let cx = &mut realm.current_realm();

        // Step 3.9

        let name = CString::new(format!("on{}", &**ty)).unwrap();

        // Step 3.9, subsection ParameterList
        const ARG_NAMES: &[*const c_char] = &[c"event".as_ptr()];
        const ERROR_ARG_NAMES: &[*const c_char] = &[
            c"event".as_ptr(),
            c"source".as_ptr(),
            c"lineno".as_ptr(),
            c"colno".as_ptr(),
            c"error".as_ptr(),
        ];
        let is_error = ty == &atom!("error") && self.is::<Window>();
        let args = if is_error { ERROR_ARG_NAMES } else { ARG_NAMES };

        let url = cformat!("{}", handler.url);
        let mut options = CompileOptionsWrapper::new(cx, url, handler.line as u32);
        options.set_introduction_type(IntroductionType::EVENT_HANDLER);

        // Step 3.9, subsection Scope steps 1-6
        let scopechain = js::rust::EnvironmentChain::new(cx, SupportUnscopables::Yes);

        if let Some(element) = element {
            scopechain.append(document.reflector().get_jsobject().get());
            if let Some(form_owner) = form_owner {
                scopechain.append(form_owner.reflector().get_jsobject().get());
            }
            scopechain.append(element.reflector().get_jsobject().get());
        }

        rooted!(&in(cx) let mut handler = unsafe {
            CompileFunction(
                cx,
                scopechain.get(),
                options.ptr,
                name.as_ptr(),
                args.len() as u32,
                args.as_ptr(),
                &mut transform_u16_to_source_text(&body),
            )
        });
        if handler.get().is_null() {
            // Step 3.7
            let mut realm = enter_auto_realm(cx, self);
            report_pending_exception(&mut realm.current_realm());
            return None;
        }

        // Step 3.10 happens when we drop _ac

        // TODO Step 3.11

        // Step 3.12
        let funobj = unsafe { JS_GetFunctionObject(handler.get()) };
        assert!(!funobj.is_null());
        // Step 1.14
        if is_error {
            Some(CommonEventHandler::ErrorEventHandler(unsafe {
                OnErrorEventHandlerNonNull::new(cx, funobj)
            }))
        } else if ty == &atom!("beforeunload") {
            Some(CommonEventHandler::BeforeUnloadEventHandler(unsafe {
                OnBeforeUnloadEventHandlerNonNull::new(cx, funobj)
            }))
        } else {
            Some(CommonEventHandler::EventHandler(unsafe {
                EventHandlerNonNull::new(cx, funobj)
            }))
        }
    }

    #[expect(unsafe_code)]
    pub(crate) fn set_event_handler_common<T: CallbackContainer<crate::DomTypeHolder>>(
        &self,
        cx: &mut JSContext,
        ty: &str,
        listener: Option<Rc<T>>,
    ) {
        let event_listener = listener.map(|listener| {
            InlineEventListener::Compiled(CommonEventHandler::EventHandler(unsafe {
                EventHandlerNonNull::new(cx, listener.callback())
            }))
        });
        self.set_inline_event_listener(Atom::from(ty), event_listener);
    }

    #[expect(unsafe_code)]
    pub(crate) fn set_error_event_handler<T: CallbackContainer<crate::DomTypeHolder>>(
        &self,
        cx: &mut JSContext,
        ty: &str,
        listener: Option<Rc<T>>,
    ) {
        let event_listener = listener.map(|listener| {
            InlineEventListener::Compiled(CommonEventHandler::ErrorEventHandler(unsafe {
                OnErrorEventHandlerNonNull::new(cx, listener.callback())
            }))
        });
        self.set_inline_event_listener(Atom::from(ty), event_listener);
    }

    #[expect(unsafe_code)]
    pub(crate) fn set_beforeunload_event_handler<T: CallbackContainer<crate::DomTypeHolder>>(
        &self,
        cx: &mut JSContext,
        ty: &str,
        listener: Option<Rc<T>>,
    ) {
        let event_listener = listener.map(|listener| {
            InlineEventListener::Compiled(CommonEventHandler::BeforeUnloadEventHandler(unsafe {
                OnBeforeUnloadEventHandlerNonNull::new(cx, listener.callback())
            }))
        });
        self.set_inline_event_listener(Atom::from(ty), event_listener);
    }

    #[expect(unsafe_code)]
    pub(crate) fn get_event_handler_common<T: CallbackContainer<crate::DomTypeHolder>>(
        &self,
        cx: &mut JSContext,
        ty: &str,
    ) -> Option<Rc<T>> {
        let listener = self.get_inline_event_listener(cx, &Atom::from(ty));
        unsafe {
            listener.map(|listener| {
                CallbackContainer::new(cx, listener.parent().callback_holder().get())
            })
        }
    }

    pub(crate) fn has_handlers(&self) -> bool {
        self.handlers
            .borrow()
            .as_ref()
            .is_some_and(|handlers| !handlers.is_empty())
    }

    // https://dom.spec.whatwg.org/#concept-event-fire
    pub(crate) fn fire_event(&self, cx: &mut js::context::JSContext, name: Atom) -> bool {
        self.fire_event_with_params(
            cx,
            name,
            EventBubbles::DoesNotBubble,
            EventCancelable::NotCancelable,
            EventComposed::NotComposed,
        )
    }

    // https://dom.spec.whatwg.org/#concept-event-fire
    pub(crate) fn fire_bubbling_event(&self, cx: &mut js::context::JSContext, name: Atom) -> bool {
        self.fire_event_with_params(
            cx,
            name,
            EventBubbles::Bubbles,
            EventCancelable::NotCancelable,
            EventComposed::NotComposed,
        )
    }

    // https://dom.spec.whatwg.org/#concept-event-fire
    pub(crate) fn fire_cancelable_event(
        &self,
        cx: &mut js::context::JSContext,
        name: Atom,
    ) -> bool {
        self.fire_event_with_params(
            cx,
            name,
            EventBubbles::DoesNotBubble,
            EventCancelable::Cancelable,
            EventComposed::NotComposed,
        )
    }

    // https://dom.spec.whatwg.org/#concept-event-fire
    pub(crate) fn fire_bubbling_cancelable_event(
        &self,
        cx: &mut js::context::JSContext,
        name: Atom,
    ) -> bool {
        self.fire_event_with_params(
            cx,
            name,
            EventBubbles::Bubbles,
            EventCancelable::Cancelable,
            EventComposed::NotComposed,
        )
    }

    /// <https://dom.spec.whatwg.org/#concept-event-fire>
    pub(crate) fn fire_event_with_params(
        &self,
        cx: &mut js::context::JSContext,
        name: Atom,
        bubbles: EventBubbles,
        cancelable: EventCancelable,
        composed: EventComposed,
    ) -> bool {
        let event = Event::new(cx, &self.global(), name, bubbles, cancelable);
        event.set_composed(composed.into());
        event.fire(cx, self)
    }

    /// <https://dom.spec.whatwg.org/#dom-eventtarget-addeventlistener>
    /// and <https://dom.spec.whatwg.org/#add-an-event-listener>
    pub(crate) fn add_event_listener(
        &self,
        ty: DOMString,
        listener: Option<Rc<EventListener>>,
        options: AddEventListenerOptions,
    ) {
        if let Some(signal) = options.signal.as_ref() {
            // Step 2. If listener’s signal is not null and is aborted, then return.
            if signal.aborted() {
                return;
            }
            // Step 6. If listener’s signal is not null, then add the following abort steps to it:
            signal.add(&AbortAlgorithm::DomEventListener(
                RemovableDomEventListener {
                    event_target: Dom::from_ref(self),
                    ty: ty.clone(),
                    listener: listener.clone(),
                    options: options.parent.clone(),
                },
            ));
        }
        // Step 3. If listener’s callback is null, then return.
        let listener = match listener {
            Some(l) => l,
            None => return,
        };
        let ty = Atom::from(ty);
        let mut handlers = self.ensure_handlers();
        let entries = match handlers.entry(ty.clone()) {
            Occupied(entry) => entry.into_mut(),
            Vacant(entry) => entry.insert(EventListeners(vec![])),
        };

        let phase = if options.parent.capture {
            ListenerPhase::Capturing
        } else {
            ListenerPhase::Bubbling
        };
        // Step 4. If listener’s passive is null, then set it to the default passive value given listener’s type and eventTarget.
        let new_entry = Rc::new(RefCell::new(EventListenerEntry {
            phase,
            listener: EventListenerType::Additive(listener),
            once: options.once,
            passive: options.passive.unwrap_or(self.default_passive_value(&ty)),
            removed: false,
        }));

        // Step 5. If eventTarget’s event listener list does not contain
        // an event listener whose type is listener’s type, callback is listener’s callback,
        // and capture is listener’s capture, then append listener to eventTarget’s event listener list.
        if !entries.contains(&new_entry) {
            entries.push(new_entry);
            self.notify_listener_added(&ty);
        }
    }

    /// <https://dom.spec.whatwg.org/#dom-eventtarget-removeeventlistener>
    /// and <https://dom.spec.whatwg.org/#remove-an-event-listener>
    pub(crate) fn remove_event_listener(
        &self,
        ty: DOMString,
        listener: &Option<Rc<EventListener>>,
        options: &EventListenerOptions,
    ) {
        let Some(listener) = listener else {
            return;
        };
        let ty_atom = Atom::from(ty);
        let mut handlers = self.handlers.borrow_mut();
        if let Some(handlers) = handlers.as_mut() &&
            let Some(entries) = handlers.get_mut(&ty_atom)
        {
            let phase = if options.capture {
                ListenerPhase::Capturing
            } else {
                ListenerPhase::Bubbling
            };
            let listener_type = EventListenerType::Additive(listener.clone());
            if let Some(position) = entries
                .iter()
                .position(|e| e.borrow().listener == listener_type && e.borrow().phase == phase)
            {
                // Step 2. Set listener’s removed to true and remove listener from eventTarget’s event listener list.
                entries.remove(position).borrow_mut().removed = true;
                self.notify_listener_removed(&ty_atom);
            }
        }
    }

    /// <https://dom.spec.whatwg.org/#get-the-parent>
    pub(crate) fn get_the_parent(&self, event: &Event) -> Option<DomRoot<EventTarget>> {
        if let Some(document) = self.downcast::<Document>() {
            if event.type_() == atom!("load") || !document.has_browsing_context() {
                return None;
            } else {
                return Some(DomRoot::from_ref(document.window().upcast::<EventTarget>()));
            }
        }

        if let Some(shadow_root) = self.downcast::<ShadowRoot>() {
            if event.should_pass_shadow_boundary(shadow_root) {
                let host = shadow_root.Host();
                return Some(DomRoot::from_ref(host.upcast::<EventTarget>()));
            } else {
                return None;
            }
        }

        if let Some(node) = self.downcast::<Node>() {
            // > A node’s get the parent algorithm, given an event, returns the node’s assigned slot,
            // > if node is assigned; otherwise node’s parent.
            return node.assigned_slot().map(DomRoot::upcast).or_else(|| {
                node.GetParentNode()
                    .map(|parent| DomRoot::from_ref(parent.upcast::<EventTarget>()))
            });
        }

        // https://w3c.github.io/IndexedDB/#events
        // The get the parent algorithm for an IDBRequest returns the request's transaction.
        if let Some(request) = self.downcast::<IDBRequest>() {
            return request
                .transaction()
                .map(|tx| DomRoot::from_ref(tx.upcast::<EventTarget>()));
        }

        // The get the parent algorithm for an IDBTransaction returns the transaction's connection.
        if let Some(transaction) = self.downcast::<IDBTransaction>() {
            return Some(DomRoot::from_ref(
                transaction.get_db().upcast::<EventTarget>(),
            ));
        }

        // The get the parent algorithm for an IDBDatabase returns null.
        if self.is::<IDBDatabase>() {
            return None;
        }

        None
    }

    // FIXME: This algorithm operates on "objects", which may not be event targets.
    // All our current use-cases only work on event targets, but this might change in the future
    /// <https://dom.spec.whatwg.org/#retarget>
    pub(crate) fn retarget(&self, b: &Self) -> DomRoot<EventTarget> {
        // To retarget an object A against an object B, repeat these steps until they return an object:
        let mut a = DomRoot::from_ref(self);
        loop {
            // Step 1. If one of the following is true
            // * A is not a node
            // * A’s root is not a shadow root
            // * B is a node and A’s root is a shadow-including inclusive ancestor of B
            // then return A.
            let Some(a_node) = a.downcast::<Node>() else {
                return a;
            };
            let a_root = a_node.GetRootNode(&GetRootNodeOptions::empty());
            if !a_root.is::<ShadowRoot>() {
                return a;
            }
            if let Some(b_node) = b.downcast::<Node>() &&
                a_root.is_shadow_including_inclusive_ancestor_of(b_node)
            {
                return a;
            }

            // Step 2. Set A to A’s root’s host.
            a = DomRoot::from_ref(
                a_root
                    .downcast::<ShadowRoot>()
                    .unwrap()
                    .Host()
                    .upcast::<EventTarget>(),
            );
        }
    }

    /// <https://html.spec.whatwg.org/multipage/#event-handler-content-attributes>
    pub(crate) fn is_content_event_handler(name: &str) -> bool {
        CONTENT_EVENT_HANDLER_NAMES.contains(&name)
    }

    pub(crate) fn summarize_event_listeners_for_devtools(&self) -> Vec<EventListenerInfo> {
        let handlers = self.handlers.borrow();
        let Some(handlers) = handlers.as_ref() else {
            return Vec::new();
        };
        let mut listener_infos = Vec::with_capacity(handlers.0.len());
        for (event_type, event_listeners) in &handlers.0 {
            for event_listener in event_listeners.iter() {
                let event_listener_entry = event_listener.borrow();
                listener_infos.push(EventListenerInfo {
                    event_type: event_type.to_string(),
                    capturing: event_listener_entry.phase() == ListenerPhase::Capturing,
                });
            }
        }

        listener_infos
    }
}

impl EventTargetMethods<crate::DomTypeHolder> for EventTarget {
    /// <https://dom.spec.whatwg.org/#dom-eventtarget-eventtarget>
    fn Constructor(
        cx: &mut JSContext,
        global: &GlobalScope,
        proto: Option<HandleObject>,
    ) -> Fallible<DomRoot<EventTarget>> {
        Ok(EventTarget::new(cx, global, proto))
    }

    /// <https://dom.spec.whatwg.org/#dom-eventtarget-addeventlistener>
    fn AddEventListener(
        &self,
        ty: DOMString,
        listener: Option<Rc<EventListener>>,
        options: AddEventListenerOptionsOrBoolean,
    ) {
        self.add_event_listener(ty, listener, options.convert())
    }

    /// <https://dom.spec.whatwg.org/#dom-eventtarget-removeeventlistener>
    fn RemoveEventListener(
        &self,
        ty: DOMString,
        listener: Option<Rc<EventListener>>,
        options: EventListenerOptionsOrBoolean,
    ) {
        self.remove_event_listener(ty, &listener, &options.convert())
    }

    /// <https://dom.spec.whatwg.org/#dom-eventtarget-dispatchevent>
    fn DispatchEvent(&self, cx: &mut JSContext, event: &Event) -> Fallible<bool> {
        if event.dispatching() || !event.initialized() {
            return Err(Error::InvalidState(None));
        }
        event.set_trusted(false);
        Ok(event.dispatch(cx, self, false))
    }
}

impl VirtualMethods for EventTarget {
    fn super_type(&self) -> Option<&dyn VirtualMethods> {
        None
    }
}

impl Convert<AddEventListenerOptions> for AddEventListenerOptionsOrBoolean {
    /// <https://dom.spec.whatwg.org/#event-flatten-more>
    fn convert(self) -> AddEventListenerOptions {
        // Step 1. Let capture be the result of flattening options.
        // Step 5. Return capture, passive, once, and signal.
        match self {
            // Step 4. If options is a dictionary:
            AddEventListenerOptionsOrBoolean::AddEventListenerOptions(options) => options,
            AddEventListenerOptionsOrBoolean::Boolean(capture) => AddEventListenerOptions {
                parent: EventListenerOptions { capture },
                // Step 2. Let once be false.
                once: false,
                // Step 3. Let passive and signal be null.
                passive: None,
                signal: None,
            },
        }
    }
}

impl Convert<EventListenerOptions> for EventListenerOptionsOrBoolean {
    fn convert(self) -> EventListenerOptions {
        match self {
            EventListenerOptionsOrBoolean::EventListenerOptions(options) => options,
            EventListenerOptionsOrBoolean::Boolean(capture) => EventListenerOptions { capture },
        }
    }
}

impl OwnerWindow<crate::DomTypeHolder> for EventTarget {
    fn owner_window(&self) -> Option<DomRoot<Window>> {
        self.downcast::<Node>().map(|node| node.owner_window())
    }
}