Source code

Revision control

Other Tools

/* -*- 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_Proxy_h
#define js_Proxy_h
#include "mozilla/Maybe.h"
#include "jstypes.h" // for JS_PUBLIC_API, JS_PUBLIC_DATA
#include "js/Array.h" // JS::IsArrayAnswer
#include "js/CallNonGenericMethod.h"
#include "js/Class.h"
#include "js/HeapAPI.h" // for ObjectIsMarkedBlack
#include "js/Id.h" // for jsid
#include "js/Object.h" // JS::GetClass
#include "js/RootingAPI.h" // for Handle, MutableHandle (ptr only)
#include "js/shadow/Object.h" // JS::shadow::Object
#include "js/TypeDecls.h" // for HandleObject, HandleId, HandleValue, MutableHandleIdVector, MutableHandleValue, MutableHand...
#include "js/Value.h" // for Value, AssertValueIsNotGray, UndefinedValue, ObjectOrNullValue
namespace js {
class RegExpShared;
class JS_PUBLIC_API Wrapper;
* [SMDOC] Proxy Objects
* A proxy is a JSObject with highly customizable behavior. ES6 specifies a
* single kind of proxy, but the customization mechanisms we use to implement
* ES6 Proxy objects are also useful wherever an object with weird behavior is
* wanted. Proxies are used to implement:
* - the scope objects used by the Debugger's frame.eval() method
* (see js::GetDebugEnvironment)
* - the khuey hack, whereby a whole compartment can be blown away
* even if other compartments hold references to objects in it
* (see js::NukeCrossCompartmentWrappers)
* - XPConnect security wrappers, which protect chrome from malicious content
* (js/xpconnect/wrappers)
* - DOM objects with special property behavior, like named getters
* (dom/bindings/ generates these proxies from WebIDL)
* ### Proxies and internal methods
* ES2019 specifies 13 internal methods. The runtime semantics of just about
* everything a script can do to an object is specified in terms of these
* internal methods. For example:
* JS code ES6 internal method that gets called
* --------------------------- --------------------------------
* obj.prop obj.[[Get]](obj, "prop")
* "prop" in obj obj.[[HasProperty]]("prop")
* new obj() obj.[[Construct]](<empty argument List>)
* With regard to the implementation of these internal methods, there are three
* very different kinds of object in SpiderMonkey.
* 1. Native objects cover most objects and contain both internal slots and
* properties. JSClassOps and ObjectOps may be used to override certain
* default behaviors.
* 2. Proxy objects are composed of internal slots and a ProxyHandler. The
* handler contains C++ methods that can implement these standard (and
* non-standard) internal methods. JSClassOps and ObjectOps for the base
* ProxyObject invoke the handler methods as appropriate.
* 3. Objects with custom layouts like TypedObjects. These rely on JSClassOps
* and ObjectOps to implement internal methods.
* Native objects with custom JSClassOps / ObjectOps are used when the object
* behaves very similar to a normal object such as the ArrayObject and it's
* length property. Most usages wrapping a C++ or other type should prefer
* using a Proxy. Using the proxy approach makes it much easier to create an
* ECMAScript and JIT compatible object, particularly if using an appropriate
* base class.
* Just about anything you do to a proxy will end up going through a C++
* virtual method call. Possibly several. There's no reason the JITs and ICs
* can't specialize for particular proxies, based on the handler; but currently
* we don't do much of this, so the virtual method overhead typically is
* actually incurred.
* ### The proxy handler hierarchy
* A major use case for proxies is to forward each internal method call to
* another object, known as its target. The target can be an arbitrary JS
* object. Not every proxy has the notion of a target, however.
* To minimize code duplication, a set of abstract proxy handler classes is
* provided, from which other handlers may inherit. These abstract classes are
* organized in the following hierarchy:
* BaseProxyHandler
* |
* ForwardingProxyHandler // has a target and forwards internal methods
* |
* Wrapper // can be unwrapped to reveal target
* | // (see js::CheckedUnwrap)
* |
* CrossCompartmentWrapper // target is in another compartment;
* // implements membrane between compartments
* Example: Some DOM objects (including all the arraylike DOM objects) are
* implemented as proxies. Since these objects don't need to forward operations
* to any underlying JS object, BaseDOMProxyHandler directly subclasses
* BaseProxyHandler.
* Gecko's security wrappers are examples of cross-compartment wrappers.
* ### Proxy prototype chains
* While most ECMAScript internal methods are handled by simply calling the
* handler method, the [[GetPrototypeOf]] / [[SetPrototypeOf]] behaviors may
* follow one of two models:
* 1. A concrete prototype object (or null) is passed to object construction
* and ordinary prototype read and write applies. The prototype-related
* handler hooks are never called in this case. The [[Prototype]] slot is
* used to store the current prototype value.
* 2. TaggedProto::LazyProto is passed to NewProxyObject (or the
* ProxyOptions::lazyProto flag is set). Each read or write of the
* prototype will invoke the handler. This dynamic prototype behavior may
* be useful for wrapper-like objects. If this mode is used the
* getPrototype handler at a minimum must be implemented.
* NOTE: In this mode the [[Prototype]] internal slot is unavailable and
* must be simulated if needed. This is non-standard, but an
* appropriate handler can hide this implementation detail.
* One subtlety here is that ECMAScript has a notion of "ordinary" prototypes.
* An object that doesn't override [[GetPrototypeOf]] is considered to have an
* ordinary prototype. The getPrototypeIfOrdinary handler must be implemented
* by you or your base class. Typically model 1 will be considered "ordinary"
* and model 2 will not.
* BaseProxyHandler is the most generic kind of proxy handler. It does not make
* any assumptions about the target. Consequently, it does not provide any
* default implementation for most methods. As a convenience, a few high-level
* methods, like get() and set(), are given default implementations that work by
* calling the low-level methods, like getOwnPropertyDescriptor().
* Important: If you add a method here, you should probably also add a
* Proxy::foo entry point with an AutoEnterPolicy. If you don't, you need an
* explicit override for the method in SecurityWrapper. See bug 945826 comment
* 0.
class JS_PUBLIC_API BaseProxyHandler {
* Sometimes it's desirable to designate groups of proxy handlers as
* "similar". For this, we use the notion of a "family": A consumer-provided
* opaque pointer that designates the larger group to which this proxy
* belongs.
* If it will never be important to differentiate this proxy from others as
* part of a distinct group, nullptr may be used instead.
const void* mFamily;
* Proxy handlers can use mHasPrototype to request the following special
* treatment from the JS engine:
* - When mHasPrototype is true, the engine never calls these methods:
* has, set, enumerate, iterate. Instead, for these operations,
* it calls the "own" methods like getOwnPropertyDescriptor, hasOwn,
* defineProperty, getOwnEnumerablePropertyKeys, etc.,
* and consults the prototype chain if needed.
* - When mHasPrototype is true, the engine calls handler->get() only if
* handler->hasOwn() says an own property exists on the proxy. If not,
* it consults the prototype chain.
* This is useful because it frees the ProxyHandler from having to implement
* any behavior having to do with the prototype chain.
bool mHasPrototype;
* All proxies indicate whether they have any sort of interesting security
* policy that might prevent the caller from doing something it wants to
* the object. In the case of wrappers, this distinction is used to
* determine whether the caller may strip off the wrapper if it so desires.
bool mHasSecurityPolicy;
explicit constexpr BaseProxyHandler(const void* aFamily,
bool aHasPrototype = false,
bool aHasSecurityPolicy = false)
: mFamily(aFamily),
mHasSecurityPolicy(aHasSecurityPolicy) {}
bool hasPrototype() const { return mHasPrototype; }
bool hasSecurityPolicy() const { return mHasSecurityPolicy; }
inline const void* family() const { return mFamily; }
static size_t offsetOfFamily() { return offsetof(BaseProxyHandler, mFamily); }
virtual bool finalizeInBackground(const JS::Value& priv) const {
* Called on creation of a proxy to determine whether its finalize
* method can be finalized on the background thread.
return true;
virtual bool canNurseryAllocate() const {
* Nursery allocation is allowed if and only if it is safe to not
* run |finalize| when the ProxyObject dies.
return false;
/* Policy enforcement methods.
* enter() allows the policy to specify whether the caller may perform |act|
* on the proxy's |id| property. In the case when |act| is CALL, |id| is
* generally JSID_VOID. The |mayThrow| parameter indicates whether a
* handler that wants to throw custom exceptions when denying should do so
* or not.
* The |act| parameter to enter() specifies the action being performed.
* If |bp| is false, the method suggests that the caller throw (though it
* may still decide to squelch the error).
* We make these OR-able so that assertEnteredPolicy can pass a union of them.
* For example, get{,Own}PropertyDescriptor is invoked by calls to ::get()
* ::set(), in addition to being invoked on its own, so there are several
* valid Actions that could have been entered.
typedef uint32_t Action;
enum {
NONE = 0x00,
GET = 0x01,
SET = 0x02,
CALL = 0x04,
virtual bool enter(JSContext* cx, JS::HandleObject wrapper, JS::HandleId id,
Action act, bool mayThrow, bool* bp) const;
/* Standard internal methods. */
virtual bool getOwnPropertyDescriptor(
JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
JS::MutableHandle<mozilla::Maybe<JS::PropertyDescriptor>> desc) const = 0;
virtual bool defineProperty(JSContext* cx, JS::HandleObject proxy,
JS::HandleId id,
JS::Handle<JS::PropertyDescriptor> desc,
JS::ObjectOpResult& result) const = 0;
virtual bool ownPropertyKeys(JSContext* cx, JS::HandleObject proxy,
JS::MutableHandleIdVector props) const = 0;
virtual bool delete_(JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
JS::ObjectOpResult& result) const = 0;
* These methods are standard, but the engine does not normally call them.
* They're opt-in. See "Proxy prototype chains" above.
* getPrototype() crashes if called. setPrototype() throws a TypeError.
virtual bool getPrototype(JSContext* cx, JS::HandleObject proxy,
JS::MutableHandleObject protop) const;
virtual bool setPrototype(JSContext* cx, JS::HandleObject proxy,
JS::HandleObject proto,
JS::ObjectOpResult& result) const;
/* Non-standard but conceptual kin to {g,s}etPrototype, so these live here. */
virtual bool getPrototypeIfOrdinary(JSContext* cx, JS::HandleObject proxy,
bool* isOrdinary,
JS::MutableHandleObject protop) const = 0;
virtual bool setImmutablePrototype(JSContext* cx, JS::HandleObject proxy,
bool* succeeded) const;
virtual bool preventExtensions(JSContext* cx, JS::HandleObject proxy,
JS::ObjectOpResult& result) const = 0;
virtual bool isExtensible(JSContext* cx, JS::HandleObject proxy,
bool* extensible) const = 0;
* These standard internal methods are implemented, as a convenience, so
* that ProxyHandler subclasses don't have to provide every single method.
* The base-class implementations work by calling getOwnPropertyDescriptor()
* and going up the [[Prototype]] chain if necessary. The algorithm for this
* follows what is defined for Ordinary Objects in the ES spec.
* They do not follow any standard. When in doubt, override them.
virtual bool has(JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
bool* bp) const;
virtual bool get(JSContext* cx, JS::HandleObject proxy,
JS::HandleValue receiver, JS::HandleId id,
JS::MutableHandleValue vp) const;
virtual bool set(JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
JS::HandleValue v, JS::HandleValue receiver,
JS::ObjectOpResult& result) const;
// Use the ProxyExpando object for private fields, rather than taking the
// normal get/set/defineField paths.
virtual bool useProxyExpandoObjectForPrivateFields() const { return true; }
* [[Call]] and [[Construct]] are standard internal methods but according
* to the spec, they are not present on every object.
* SpiderMonkey never calls a proxy's call()/construct() internal method
* unless isCallable()/isConstructor() returns true for that proxy.
* BaseProxyHandler::isCallable()/isConstructor() always return false, and
* BaseProxyHandler::call()/construct() crash if called. So if you're
* creating a kind of that is never callable, you don't have to override
* anything, but otherwise you probably want to override all four.
virtual bool call(JSContext* cx, JS::HandleObject proxy,
const JS::CallArgs& args) const;
virtual bool construct(JSContext* cx, JS::HandleObject proxy,
const JS::CallArgs& args) const;
/* SpiderMonkey extensions. */
virtual bool enumerate(JSContext* cx, JS::HandleObject proxy,
JS::MutableHandleIdVector props) const;
virtual bool hasOwn(JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
bool* bp) const;
virtual bool getOwnEnumerablePropertyKeys(
JSContext* cx, JS::HandleObject proxy,
JS::MutableHandleIdVector props) const;
virtual bool nativeCall(JSContext* cx, JS::IsAcceptableThis test,
JS::NativeImpl impl, const JS::CallArgs& args) const;
virtual bool hasInstance(JSContext* cx, JS::HandleObject proxy,
JS::MutableHandleValue v, bool* bp) const;
virtual bool getBuiltinClass(JSContext* cx, JS::HandleObject proxy,
ESClass* cls) const;
virtual bool isArray(JSContext* cx, JS::HandleObject proxy,
JS::IsArrayAnswer* answer) const;
virtual const char* className(JSContext* cx, JS::HandleObject proxy) const;
virtual JSString* fun_toString(JSContext* cx, JS::HandleObject proxy,
bool isToSource) const;
virtual RegExpShared* regexp_toShared(JSContext* cx,
JS::HandleObject proxy) const;
virtual bool boxedValue_unbox(JSContext* cx, JS::HandleObject proxy,
JS::MutableHandleValue vp) const;
virtual void trace(JSTracer* trc, JSObject* proxy) const;
virtual void finalize(JSFreeOp* fop, JSObject* proxy) const;
virtual size_t objectMoved(JSObject* proxy, JSObject* old) const;
// Allow proxies, wrappers in particular, to specify callability at runtime.
// Note: These do not take const JSObject*, but they do in spirit.
// We are not prepared to do this, as there's little const correctness
// in the external APIs that handle proxies.
virtual bool isCallable(JSObject* obj) const;
virtual bool isConstructor(JSObject* obj) const;
virtual bool getElements(JSContext* cx, JS::HandleObject proxy,
uint32_t begin, uint32_t end,
ElementAdder* adder) const;
virtual bool isScripted() const { return false; }
extern JS_PUBLIC_DATA const JSClass ProxyClass;
inline bool IsProxy(const JSObject* obj) {
return JS::GetClass(obj)->isProxyObject();
namespace detail {
// Proxy slot layout
// -----------------
// Every proxy has a ProxyValueArray that contains the following Values:
// - The expando slot. This is used to hold private fields should they be
// stamped into a non-forwarding proxy type.
// - The private slot.
// - The reserved slots. The number of slots is determined by the proxy's Class.
// Proxy objects store a pointer to the reserved slots (ProxyReservedSlots*).
// The ProxyValueArray and the private slot can be accessed using
// ProxyValueArray::fromReservedSlots or ProxyDataLayout::values.
// Storing a pointer to ProxyReservedSlots instead of ProxyValueArray has a
// number of advantages. In particular, it means JS::GetReservedSlot and
// JS::SetReservedSlot can be used with both proxies and native objects. This
// works because the ProxyReservedSlots* pointer is stored where native objects
// store their dynamic slots pointer.
struct ProxyReservedSlots {
JS::Value slots[1];
static inline int offsetOfPrivateSlot();
static inline int offsetOfSlot(size_t slot) {
return offsetof(ProxyReservedSlots, slots[0]) + slot * sizeof(JS::Value);
void init(size_t nreserved) {
for (size_t i = 0; i < nreserved; i++) {
slots[i] = JS::UndefinedValue();
ProxyReservedSlots(const ProxyReservedSlots&) = delete;
void operator=(const ProxyReservedSlots&) = delete;
struct ProxyValueArray {
JS::Value expandoSlot;
JS::Value privateSlot;
ProxyReservedSlots reservedSlots;
void init(size_t nreserved) {
expandoSlot = JS::ObjectOrNullValue(nullptr);
privateSlot = JS::UndefinedValue();
static size_t sizeOf(size_t nreserved) {
return offsetOfReservedSlots() + nreserved * sizeof(JS::Value);
static MOZ_ALWAYS_INLINE ProxyValueArray* fromReservedSlots(
ProxyReservedSlots* slots) {
uintptr_t p = reinterpret_cast<uintptr_t>(slots);
return reinterpret_cast<ProxyValueArray*>(p - offsetOfReservedSlots());
static size_t offsetOfReservedSlots() {
return offsetof(ProxyValueArray, reservedSlots);
ProxyValueArray(const ProxyValueArray&) = delete;
void operator=(const ProxyValueArray&) = delete;
/* static */ inline int ProxyReservedSlots::offsetOfPrivateSlot() {
return -int(ProxyValueArray::offsetOfReservedSlots()) +
offsetof(ProxyValueArray, privateSlot);
// All proxies share the same data layout. Following the object's shape and
// type, the proxy has a ProxyDataLayout structure with a pointer to an array
// of values and the proxy's handler. This is designed both so that proxies can
// be easily swapped with other objects (via RemapWrapper) and to mimic the
// layout of other objects (proxies and other objects have the same size) so
// that common code can access either type of object.
// See GetReservedOrProxyPrivateSlot below.
struct ProxyDataLayout {
ProxyReservedSlots* reservedSlots;
const BaseProxyHandler* handler;
MOZ_ALWAYS_INLINE ProxyValueArray* values() const {
return ProxyValueArray::fromReservedSlots(reservedSlots);
#ifdef JS_64BIT
constexpr uint32_t ProxyDataOffset = 1 * sizeof(void*);
constexpr uint32_t ProxyDataOffset = 2 * sizeof(void*);
inline ProxyDataLayout* GetProxyDataLayout(JSObject* obj) {
return reinterpret_cast<ProxyDataLayout*>(reinterpret_cast<uint8_t*>(obj) +
inline const ProxyDataLayout* GetProxyDataLayout(const JSObject* obj) {
return reinterpret_cast<const ProxyDataLayout*>(
reinterpret_cast<const uint8_t*>(obj) + ProxyDataOffset);
JS_PUBLIC_API void SetValueInProxy(JS::Value* slot, const JS::Value& value);
inline void SetProxyReservedSlotUnchecked(JSObject* obj, size_t n,
const JS::Value& extra) {
JS::Value* vp = &GetProxyDataLayout(obj)->reservedSlots->slots[n];
// Trigger a barrier before writing the slot.
if (vp->isGCThing() || extra.isGCThing()) {
SetValueInProxy(vp, extra);
} else {
*vp = extra;
} // namespace detail
inline const BaseProxyHandler* GetProxyHandler(const JSObject* obj) {
return detail::GetProxyDataLayout(obj)->handler;
inline const JS::Value& GetProxyPrivate(const JSObject* obj) {
return detail::GetProxyDataLayout(obj)->values()->privateSlot;
inline const JS::Value& GetProxyExpando(const JSObject* obj) {
return detail::GetProxyDataLayout(obj)->values()->expandoSlot;
inline JSObject* GetProxyTargetObject(const JSObject* obj) {
return GetProxyPrivate(obj).toObjectOrNull();
inline const JS::Value& GetProxyReservedSlot(const JSObject* obj, size_t n) {
return detail::GetProxyDataLayout(obj)->reservedSlots->slots[n];
inline void SetProxyHandler(JSObject* obj, const BaseProxyHandler* handler) {
detail::GetProxyDataLayout(obj)->handler = handler;
inline void SetProxyReservedSlot(JSObject* obj, size_t n,
const JS::Value& extra) {
#ifdef DEBUG
if (gc::detail::ObjectIsMarkedBlack(obj)) {
detail::SetProxyReservedSlotUnchecked(obj, n, extra);
inline void SetProxyPrivate(JSObject* obj, const JS::Value& value) {
#ifdef DEBUG
if (gc::detail::ObjectIsMarkedBlack(obj)) {
JS::Value* vp = &detail::GetProxyDataLayout(obj)->values()->privateSlot;
// Trigger a barrier before writing the slot.
if (vp->isGCThing() || value.isGCThing()) {
detail::SetValueInProxy(vp, value);
} else {
*vp = value;
inline bool IsScriptedProxy(const JSObject* obj) {
return IsProxy(obj) && GetProxyHandler(obj)->isScripted();
class MOZ_STACK_CLASS ProxyOptions {
/* protected constructor for subclass */
explicit ProxyOptions(bool lazyProtoArg)
: lazyProto_(lazyProtoArg), clasp_(&ProxyClass) {}
ProxyOptions() : ProxyOptions(false) {}
bool lazyProto() const { return lazyProto_; }
ProxyOptions& setLazyProto(bool flag) {
lazyProto_ = flag;
return *this;
const JSClass* clasp() const { return clasp_; }
ProxyOptions& setClass(const JSClass* claspArg) {
clasp_ = claspArg;
return *this;
bool lazyProto_;
const JSClass* clasp_;
JS_PUBLIC_API JSObject* NewProxyObject(
JSContext* cx, const BaseProxyHandler* handler, JS::HandleValue priv,
JSObject* proto, const ProxyOptions& options = ProxyOptions());
JSObject* RenewProxyObject(JSContext* cx, JSObject* obj,
BaseProxyHandler* handler, const JS::Value& priv);
class JS_PUBLIC_API AutoEnterPolicy {
typedef BaseProxyHandler::Action Action;
AutoEnterPolicy(JSContext* cx, const BaseProxyHandler* handler,
JS::HandleObject wrapper, JS::HandleId id, Action act,
bool mayThrow)
#ifdef JS_DEBUG
: context(nullptr)
allow = handler->hasSecurityPolicy()
? handler->enter(cx, wrapper, id, act, mayThrow, &rv)
: true;
recordEnter(cx, wrapper, id, act);
// We want to throw an exception if all of the following are true:
// * The policy disallowed access.
// * The policy set rv to false, indicating that we should throw.
// * The caller did not instruct us to ignore exceptions.
// * The policy did not throw itself.
if (!allow && !rv && mayThrow) {
reportErrorIfExceptionIsNotPending(cx, id);
virtual ~AutoEnterPolicy() { recordLeave(); }
inline bool allowed() { return allow; }
inline bool returnValue() {
return rv;
// no-op constructor for subclass
#ifdef JS_DEBUG
: context(nullptr),
void reportErrorIfExceptionIsNotPending(JSContext* cx, JS::HandleId id);
bool allow;
bool rv;
#ifdef JS_DEBUG
JSContext* context;
mozilla::Maybe<JS::HandleObject> enteredProxy;
mozilla::Maybe<JS::HandleId> enteredId;
Action enteredAction;
// NB: We explicitly don't track the entered action here, because sometimes
// set() methods do an implicit get() during their implementation, leading
// to spurious assertions.
AutoEnterPolicy* prev;
void recordEnter(JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
Action act);
void recordLeave();
friend JS_PUBLIC_API void assertEnteredPolicy(JSContext* cx, JSObject* proxy,
jsid id, Action act);
inline void recordEnter(JSContext* cx, JSObject* proxy, jsid id, Action act) {
inline void recordLeave() {}
// This operator needs to be deleted explicitly, otherwise Visual C++ will
// create it automatically when it is part of the export JS API. In that
// case, compile would fail because HandleId is not allowed to be assigned
// and consequently instantiation of assign operator of mozilla::Maybe
// would fail. See bug 1325351 comment 16. Copy constructor is removed at
// the same time for consistency.
AutoEnterPolicy(const AutoEnterPolicy&) = delete;
AutoEnterPolicy& operator=(const AutoEnterPolicy&) = delete;
#ifdef JS_DEBUG
class JS_PUBLIC_API AutoWaivePolicy : public AutoEnterPolicy {
AutoWaivePolicy(JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
BaseProxyHandler::Action act) {
allow = true;
recordEnter(cx, proxy, id, act);
class JS_PUBLIC_API AutoWaivePolicy {
AutoWaivePolicy(JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
BaseProxyHandler::Action act) {}
#ifdef JS_DEBUG
extern JS_PUBLIC_API void assertEnteredPolicy(JSContext* cx, JSObject* obj,
jsid id,
BaseProxyHandler::Action act);
inline void assertEnteredPolicy(JSContext* cx, JSObject* obj, jsid id,
BaseProxyHandler::Action act) {}
extern JS_PUBLIC_DATA const JSClassOps ProxyClassOps;
extern JS_PUBLIC_DATA const js::ClassExtension ProxyClassExtension;
extern JS_PUBLIC_DATA const js::ObjectOps ProxyObjectOps;
template <unsigned Flags>
constexpr unsigned CheckProxyFlags() {
constexpr size_t reservedSlots =
// For now assert each Proxy Class has at least 1 reserved slot. This is
// not a hard requirement, but helps catch Classes that need an explicit
// JSCLASS_HAS_RESERVED_SLOTS since bug 1360523.
static_assert(reservedSlots > 0,
"Proxy Classes must have at least 1 reserved slot");
constexpr size_t numSlots =
offsetof(js::detail::ProxyValueArray, reservedSlots) / sizeof(JS::Value);
// ProxyValueArray must fit inline in the object, so assert the number of
// slots does not exceed MAX_FIXED_SLOTS.
static_assert(numSlots + reservedSlots <= JS::shadow::Object::MAX_FIXED_SLOTS,
"ProxyValueArray size must not exceed max JSObject size");
// Proxies must not have the JSCLASS_SKIP_NURSERY_FINALIZE flag set: they
// always have finalizers, and whether they can be nursery allocated is
// controlled by the canNurseryAllocate() method on the proxy handler.
static_assert(!(Flags & JSCLASS_SKIP_NURSERY_FINALIZE),
"Proxies must not use JSCLASS_SKIP_NURSERY_FINALIZE; use "
"the canNurseryAllocate() proxy handler method instead.");
return Flags;
#define PROXY_CLASS_DEF_WITH_CLASS_SPEC(name, flags, classSpec) \
{ \
name, \
JSCLASS_DELAY_METADATA_BUILDER | js::CheckProxyFlags<flags>(), \
&js::ProxyClassOps, classSpec, &js::ProxyClassExtension, \
&js::ProxyObjectOps \
#define PROXY_CLASS_DEF(name, flags) \
// Converts a proxy into a DeadObjectProxy that will throw exceptions on all
// access. This will run the proxy's finalizer to perform clean-up before the
// conversion happens.
JS_PUBLIC_API void NukeNonCCWProxy(JSContext* cx, JS::HandleObject proxy);
// This is a variant of js::NukeNonCCWProxy() for CCWs. It should only be called
// on CCWs that have been removed from CCW tables.
JS_PUBLIC_API void NukeRemovedCrossCompartmentWrapper(JSContext* cx,
JSObject* wrapper);
} /* namespace js */
#endif /* js_Proxy_h */