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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* 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 */
#ifndef js_public_Object_h
#define js_public_Object_h
#include "js/shadow/Object.h" // JS::shadow::Object
#include "mozilla/Assertions.h" // MOZ_ASSERT
#include <stddef.h> // size_t
#include <stdint.h> // uint32_t
#include "jstypes.h" // JS_PUBLIC_API
#include "js/Class.h" // js::ESClass, JSCLASS_RESERVED_SLOTS
#include "js/Realm.h" // JS::GetCompartmentForRealm
#include "js/RootingAPI.h" // JS::{,Mutable}Handle
#include "js/Value.h" // JS::Value
struct JS_PUBLIC_API JSContext;
class JS_PUBLIC_API JSObject;
namespace JS {
class JS_PUBLIC_API Compartment;
* Determine the ECMAScript "class" -- Date, String, RegExp, and all the other
* builtin object types (described in ECMAScript in terms of an objecting having
* "an [[ArrayBufferData]] internal slot" or similar language for other kinds of
* object -- of the provided object.
* If this function is passed a wrapper that can be unwrapped, the determination
* is performed on that object. If the wrapper can't be unwrapped, and it's not
* a wrapper that prefers to treat this operation as a failure, this function
* will indicate that the object is |js::ESClass::Other|.
extern JS_PUBLIC_API bool GetBuiltinClass(JSContext* cx, Handle<JSObject*> obj,
js::ESClass* cls);
/** Get the |JSClass| of an object. */
inline const JSClass* GetClass(const JSObject* obj) {
return reinterpret_cast<const shadow::Object*>(obj)->shape->base->clasp;
* Get the |JS::Compartment*| of an object.
* Note that the compartment of an object in this realm, that is a
* cross-compartment wrapper around an object from another realm, is the
* compartment of this realm.
static MOZ_ALWAYS_INLINE Compartment* GetCompartment(JSObject* obj) {
Realm* realm = reinterpret_cast<shadow::Object*>(obj)->shape->base->realm;
return GetCompartmentForRealm(realm);
* Get the value stored in a reserved slot in an object.
* If |obj| is known to be a proxy and you're willing to use friend APIs,
* |js::GetProxyReservedSlot| in "js/Proxy.h" is very slightly more efficient.
inline const Value& GetReservedSlot(JSObject* obj, size_t slot) {
return reinterpret_cast<const shadow::Object*>(obj)->slotRef(slot);
namespace detail {
extern JS_PUBLIC_API void SetReservedSlotWithBarrier(JSObject* obj, size_t slot,
const Value& value);
} // namespace detail
* Store a value in an object's reserved slot.
* This can be used with both native objects and proxies. However, if |obj| is
* known to be a proxy, |js::SetProxyReservedSlot| in "js/Proxy.h" is very
* slightly more efficient.
inline void SetReservedSlot(JSObject* obj, size_t slot, const Value& value) {
auto* sobj = reinterpret_cast<shadow::Object*>(obj);
if (sobj->slotRef(slot).isGCThing() || value.isGCThing()) {
detail::SetReservedSlotWithBarrier(obj, slot, value);
} else {
sobj->slotRef(slot) = value;
* Helper function to get the pointer value (or nullptr if not set) from an
* object's reserved slot. The slot must contain either a PrivateValue(T*) or
* UndefinedValue.
template <typename T>
inline T* GetMaybePtrFromReservedSlot(JSObject* obj, size_t slot) {
Value v = GetReservedSlot(obj, slot);
return v.isUndefined() ? nullptr : static_cast<T*>(v.toPrivate());
* Helper function to get the pointer value (or nullptr if not set) from the
* object's first reserved slot. Must only be used for objects with a JSClass
* that has the JSCLASS_SLOT0_IS_NSISUPPORTS flag.
template <typename T>
inline T* GetObjectISupports(JSObject* obj) {
return GetMaybePtrFromReservedSlot<T>(obj, 0);
* Helper function to store |PrivateValue(nsISupportsValue)| in the object's
* first reserved slot. Must only be used for objects with a JSClass that has
* Note: the pointer is opaque to the JS engine (including the GC) so it's the
* embedding's responsibility to trace or free this value.
inline void SetObjectISupports(JSObject* obj, void* nsISupportsValue) {
SetReservedSlot(obj, 0, PrivateValue(nsISupportsValue));
} // namespace JS
// JSObject* is an aligned pointer, but this information isn't available in the
// public header. We specialize HasFreeLSB here so that JS::Result<JSObject*>
// compiles.
namespace mozilla {
namespace detail {
template <>
struct HasFreeLSB<JSObject*> {
static constexpr bool value = true;
} // namespace detail
} // namespace mozilla
#endif // js_public_Object_h