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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 */
/* JSClass definition and its component types, plus related interfaces. */
#ifndef js_Class_h
#define js_Class_h
#include "mozilla/Attributes.h"
#include "mozilla/Maybe.h"
#include "jstypes.h"
#include "js/CallArgs.h"
#include "js/HeapAPI.h"
#include "js/Id.h"
#include "js/TypeDecls.h"
* A JSClass acts as a vtable for JS objects that allows JSAPI clients to
* control various aspects of the behavior of an object like property lookup.
* It contains some engine-private extensions that allows more control over
* object behavior and, e.g., allows custom slow layout.
struct JSAtomState;
struct JSFunctionSpec;
namespace js {
class PropertyResult;
// These are equal to js::FunctionClass / js::ExtendedFunctionClass.
extern JS_PUBLIC_DATA const JSClass* const FunctionClassPtr;
extern JS_PUBLIC_DATA const JSClass* const FunctionExtendedClassPtr;
} // namespace js
namespace JS {
* Per ES6, the [[DefineOwnProperty]] internal method has three different
* possible outcomes:
* - It can throw an exception (which we indicate by returning false).
* - It can return true, indicating unvarnished success.
* - It can return false, indicating "strict failure". The property could
* not be defined. It's an error, but no exception was thrown.
* It's not just [[DefineOwnProperty]]: all the mutating internal methods have
* the same three outcomes. (The other affected internal methods are [[Set]],
* [[Delete]], [[SetPrototypeOf]], and [[PreventExtensions]].)
* If you think this design is awful, you're not alone. But as it's the
* standard, we must represent these boolean "success" values somehow.
* ObjectOpSuccess is the class for this. It's like a bool, but when it's false
* it also stores an error code.
* Typical usage:
* ObjectOpResult result;
* if (!DefineProperty(cx, obj, id, ..., result)) {
* return false;
* }
* if (!result) {
* return result.reportError(cx, obj, id);
* }
* Users don't have to call ``; another possible ending is:
* argv.rval().setBoolean(result.ok());
* return true;
class ObjectOpResult {
* code_ is either one of the special codes OkCode or Uninitialized, or an
* error code. For now the error codes are JS friend API and are defined in
* js/public/friend/ErrorNumbers.msg.
* code_ is uintptr_t (rather than uint32_t) for the convenience of the
* JITs, which would otherwise have to deal with either padding or stack
* alignment on 64-bit platforms.
uintptr_t code_;
enum SpecialCodes : uintptr_t { OkCode = 0, Uninitialized = uintptr_t(-1) };
ObjectOpResult() : code_(Uninitialized) {}
/* Return true if succeed() was called. */
bool ok() const {
MOZ_ASSERT(code_ != Uninitialized);
return code_ == OkCode;
explicit operator bool() const { return ok(); }
/* Set this ObjectOpResult to true and return true. */
bool succeed() {
code_ = OkCode;
return true;
* Set this ObjectOpResult to false with an error code.
* Always returns true, as a convenience. Typical usage will be:
* if (funny condition) {
* return;
* }
* The true return value indicates that no exception is pending, and it
* would be OK to ignore the failure and continue.
bool fail(uint32_t msg) {
MOZ_ASSERT(msg != OkCode);
code_ = msg;
return true;
JS_PUBLIC_API bool failCantRedefineProp();
JS_PUBLIC_API bool failReadOnly();
JS_PUBLIC_API bool failGetterOnly();
JS_PUBLIC_API bool failCantDelete();
JS_PUBLIC_API bool failCantSetInterposed();
JS_PUBLIC_API bool failCantDefineWindowElement();
JS_PUBLIC_API bool failCantDeleteWindowElement();
JS_PUBLIC_API bool failCantDefineWindowNamedProperty();
JS_PUBLIC_API bool failCantDeleteWindowNamedProperty();
JS_PUBLIC_API bool failCantPreventExtensions();
JS_PUBLIC_API bool failCantSetProto();
JS_PUBLIC_API bool failNoNamedSetter();
JS_PUBLIC_API bool failNoIndexedSetter();
JS_PUBLIC_API bool failNotDataDescriptor();
JS_PUBLIC_API bool failInvalidDescriptor();
// Careful: This case has special handling in Object.defineProperty.
JS_PUBLIC_API bool failCantDefineWindowNonConfigurable();
JS_PUBLIC_API bool failBadArrayLength();
JS_PUBLIC_API bool failBadIndex();
uint32_t failureCode() const {
return uint32_t(code_);
* Report an error if necessary; return true to proceed and
* false if an error was reported.
* The precise rules are like this:
* - If ok(), then we succeeded. Do nothing and return true.
* - Otherwise, if |strict| is true, throw a TypeError and return false.
* - Otherwise, do nothing and return true.
bool checkStrictModeError(JSContext* cx, HandleObject obj, HandleId id,
bool strict) {
if (ok() || !strict) {
return true;
return reportError(cx, obj, id);
* The same as checkStrictModeError(cx, id, strict), except the
* operation is not associated with a particular property id. This is
* used for [[PreventExtensions]] and [[SetPrototypeOf]]. failureCode()
* must not be an error that has "{0}" in the error message.
bool checkStrictModeError(JSContext* cx, HandleObject obj, bool strict) {
if (ok() || !strict) {
return true;
return reportError(cx, obj);
/* Throw a TypeError. Call this only if !ok(). */
bool reportError(JSContext* cx, HandleObject obj, HandleId id);
* The same as reportError(cx, obj, id), except the operation is not
* associated with a particular property id.
bool reportError(JSContext* cx, HandleObject obj);
// Convenience method. Return true if ok(); otherwise throw a TypeError
// and return false.
bool checkStrict(JSContext* cx, HandleObject obj, HandleId id) {
return checkStrictModeError(cx, obj, id, true);
// Convenience method. The same as checkStrict(cx, obj, id), except the
// operation is not associated with a particular property id.
bool checkStrict(JSContext* cx, HandleObject obj) {
return checkStrictModeError(cx, obj, true);
} // namespace JS
// JSClass operation signatures.
/** Add a property named by id to obj. */
typedef bool (*JSAddPropertyOp)(JSContext* cx, JS::HandleObject obj,
JS::HandleId id, JS::HandleValue v);
* Delete a property named by id in obj.
* If an error occurred, return false as per normal JSAPI error practice.
* If no error occurred, but the deletion attempt wasn't allowed (perhaps
* because the property was non-configurable), call and
* return true. This will cause |delete obj[id]| to evaluate to false in
* non-strict mode code, and to throw a TypeError in strict mode code.
* If no error occurred and the deletion wasn't disallowed (this is *not* the
* same as saying that a deletion actually occurred -- deleting a non-existent
* property, or an inherited property, is allowed -- it's just pointless),
* call result.succeed() and return true.
typedef bool (*JSDeletePropertyOp)(JSContext* cx, JS::HandleObject obj,
JS::HandleId id, JS::ObjectOpResult& result);
* The type of ObjectOps::enumerate. This callback overrides a portion of
* SpiderMonkey's default [[Enumerate]] internal method. When an ordinary object
* is enumerated, that object and each object on its prototype chain is tested
* for an enumerate op, and those ops are called in order. The properties each
* op adds to the 'properties' vector are added to the set of values the for-in
* loop will iterate over. All of this is nonstandard.
* An object is "enumerated" when it's the target of a for-in loop or
* JS_Enumerate(). The callback's job is to populate 'properties' with the
* object's property keys. If `enumerableOnly` is true, the callback should only
* add enumerable properties.
typedef bool (*JSNewEnumerateOp)(JSContext* cx, JS::HandleObject obj,
JS::MutableHandleIdVector properties,
bool enumerableOnly);
* The old-style JSClass.enumerate op should define all lazy properties not
* yet reflected in obj.
typedef bool (*JSEnumerateOp)(JSContext* cx, JS::HandleObject obj);
* The type of ObjectOps::funToString. This callback allows an object to
* provide a custom string to use when Function.prototype.toString is invoked on
* that object. A null return value means OOM.
typedef JSString* (*JSFunToStringOp)(JSContext* cx, JS::HandleObject obj,
bool isToSource);
* Resolve a lazy property named by id in obj by defining it directly in obj.
* Lazy properties are those reflected from some peer native property space
* (e.g., the DOM attributes for a given node reflected as obj) on demand.
* JS looks for a property in an object, and if not found, tries to resolve
* the given id. *resolvedp should be set to true iff the property was defined
* on |obj|.
* See JS::dbg::ShouldAvoidSideEffects in Debug.h if this function has any
* other side-effect than just resolving the property.
typedef bool (*JSResolveOp)(JSContext* cx, JS::HandleObject obj,
JS::HandleId id, bool* resolvedp);
* A class with a resolve hook can optionally have a mayResolve hook. This hook
* must have no side effects and must return true for a given id if the resolve
* hook may resolve this id. This is useful when we're doing a "pure" lookup: if
* mayResolve returns false, we know we don't have to call the effectful resolve
* hook.
* maybeObj, if non-null, is the object on which we're doing the lookup. This
* can be nullptr: during JIT compilation we sometimes know the Class but not
* the object.
typedef bool (*JSMayResolveOp)(const JSAtomState& names, jsid id,
JSObject* maybeObj);
* Finalize obj, which the garbage collector has determined to be unreachable
* from other live objects or from GC roots. Obviously, finalizers must never
* store a reference to obj.
typedef void (*JSFinalizeOp)(JS::GCContext* gcx, JSObject* obj);
* Function type for trace operation of the class called to enumerate all
* traceable things reachable from obj's private data structure. For each such
* thing, a trace implementation must call JS::TraceEdge on the thing's
* location.
* JSTraceOp implementation can assume that no other threads mutates object
* state. It must not change state of the object or corresponding native
* structures. The only exception for this rule is the case when the embedding
* needs a tight integration with GC. In that case the embedding can check if
* the traversal is a part of the marking phase through calling
* JS_IsGCMarkingTracer and apply a special code like emptying caches or
* marking its native structures.
typedef void (*JSTraceOp)(JSTracer* trc, JSObject* obj);
typedef size_t (*JSObjectMovedOp)(JSObject* obj, JSObject* old);
namespace js {
/* Internal / friend API operation signatures. */
typedef bool (*LookupPropertyOp)(JSContext* cx, JS::HandleObject obj,
JS::HandleId id, JS::MutableHandleObject objp,
PropertyResult* propp);
typedef bool (*DefinePropertyOp)(JSContext* cx, JS::HandleObject obj,
JS::HandleId id,
JS::Handle<JS::PropertyDescriptor> desc,
JS::ObjectOpResult& result);
typedef bool (*HasPropertyOp)(JSContext* cx, JS::HandleObject obj,
JS::HandleId id, bool* foundp);
typedef bool (*GetPropertyOp)(JSContext* cx, JS::HandleObject obj,
JS::HandleValue receiver, JS::HandleId id,
JS::MutableHandleValue vp);
typedef bool (*SetPropertyOp)(JSContext* cx, JS::HandleObject obj,
JS::HandleId id, JS::HandleValue v,
JS::HandleValue receiver,
JS::ObjectOpResult& result);
typedef bool (*GetOwnPropertyOp)(
JSContext* cx, JS::HandleObject obj, JS::HandleId id,
JS::MutableHandle<mozilla::Maybe<JS::PropertyDescriptor>> desc);
typedef bool (*DeletePropertyOp)(JSContext* cx, JS::HandleObject obj,
JS::HandleId id, JS::ObjectOpResult& result);
class JS_PUBLIC_API ElementAdder {
enum GetBehavior {
// Check if the element exists before performing the Get and preserve
// holes.
// Perform a Get operation, like obj[index] in JS.
// Only one of these is used.
JS::RootedObject resObj_;
JS::Value* vp_;
uint32_t index_;
#ifdef DEBUG
uint32_t length_;
GetBehavior getBehavior_;
ElementAdder(JSContext* cx, JSObject* obj, uint32_t length,
GetBehavior behavior)
: resObj_(cx, obj),
#ifdef DEBUG
getBehavior_(behavior) {
ElementAdder(JSContext* cx, JS::Value* vp, uint32_t length,
GetBehavior behavior)
: resObj_(cx),
#ifdef DEBUG
getBehavior_(behavior) {
GetBehavior getBehavior() const { return getBehavior_; }
bool append(JSContext* cx, JS::HandleValue v);
void appendHole();
typedef bool (*GetElementsOp)(JSContext* cx, JS::HandleObject obj,
uint32_t begin, uint32_t end,
ElementAdder* adder);
/** Callback for the creation of constructor and prototype objects. */
typedef JSObject* (*ClassObjectCreationOp)(JSContext* cx, JSProtoKey key);
* Callback for custom post-processing after class initialization via
* ClassSpec.
typedef bool (*FinishClassInitOp)(JSContext* cx, JS::HandleObject ctor,
JS::HandleObject proto);
struct MOZ_STATIC_CLASS ClassSpec {
ClassObjectCreationOp createConstructor;
ClassObjectCreationOp createPrototype;
const JSFunctionSpec* constructorFunctions;
const JSPropertySpec* constructorProperties;
const JSFunctionSpec* prototypeFunctions;
const JSPropertySpec* prototypeProperties;
FinishClassInitOp finishInit;
uintptr_t flags;
static const size_t ProtoKeyWidth = JSCLASS_CACHED_PROTO_WIDTH;
static const uintptr_t ProtoKeyMask = (1 << ProtoKeyWidth) - 1;
static const uintptr_t DontDefineConstructor = 1 << ProtoKeyWidth;
bool defined() const { return !!createConstructor; }
// The ProtoKey this class inherits from.
JSProtoKey inheritanceProtoKey() const {
static_assert(JSProto_Null == 0, "zeroed key must be null");
// Default: Inherit from Object.
if (!(flags & ProtoKeyMask)) {
return JSProto_Object;
return JSProtoKey(flags & ProtoKeyMask);
bool shouldDefineConstructor() const {
return !(flags & DontDefineConstructor);
struct MOZ_STATIC_CLASS ClassExtension {
* Optional hook called when an object is moved by generational or
* compacting GC.
* There may exist weak pointers to an object that are not traced through
* when the normal trace APIs are used, for example objects in the wrapper
* cache. This hook allows these pointers to be updated.
* Note that this hook can be called before JS_NewObject() returns if a GC
* is triggered during construction of the object. This can happen for
* global objects for example.
* The function should return the difference between nursery bytes used and
* tenured bytes used, which may be nonzero e.g. if some nursery-allocated
* data beyond the actual GC thing is moved into malloced memory.
* This is used to compute the nursery promotion rate.
JSObjectMovedOp objectMovedOp;
struct MOZ_STATIC_CLASS ObjectOps {
LookupPropertyOp lookupProperty;
DefinePropertyOp defineProperty;
HasPropertyOp hasProperty;
GetPropertyOp getProperty;
SetPropertyOp setProperty;
GetOwnPropertyOp getOwnPropertyDescriptor;
DeletePropertyOp deleteProperty;
GetElementsOp getElements;
JSFunToStringOp funToString;
} // namespace js
static constexpr const js::ClassSpec* JS_NULL_CLASS_SPEC = nullptr;
static constexpr const js::ClassExtension* JS_NULL_CLASS_EXT = nullptr;
static constexpr const js::ObjectOps* JS_NULL_OBJECT_OPS = nullptr;
// Classes, objects, and properties.
// (1 << 0 is unused)
// Class's initialization code will call `SetNewObjectMetadata` itself.
static const uint32_t JSCLASS_DELAY_METADATA_BUILDER = 1 << 1;
// Class is an XPCWrappedNative. WeakMaps use this to override the wrapper
// disposal mechanism.
static const uint32_t JSCLASS_IS_WRAPPED_NATIVE = 1 << 2;
// First reserved slot is `PrivateValue(nsISupports*)` or `UndefinedValue`.
static constexpr uint32_t JSCLASS_SLOT0_IS_NSISUPPORTS = 1 << 3;
// Objects are DOM.
static const uint32_t JSCLASS_IS_DOMJSCLASS = 1 << 4;
// If wrapped by an xray wrapper, the builtin class's constructor won't be
// unwrapped and invoked. Instead, the constructor is resolved in the caller's
// compartment and invoked with a wrapped newTarget. The constructor has to
// detect and handle this situation. See PromiseConstructor for details.
static const uint32_t JSCLASS_HAS_XRAYED_CONSTRUCTOR = 1 << 5;
// Objects of this class act like the value undefined, in some contexts.
static const uint32_t JSCLASS_EMULATES_UNDEFINED = 1 << 6;
// Reserved for embeddings.
static const uint32_t JSCLASS_USERBIT1 = 1 << 7;
// To reserve slots fetched and stored via JS_Get/SetReservedSlot, bitwise-or
// JSCLASS_HAS_RESERVED_SLOTS(n) into the initializer for JSClass.flags, where n
// is a constant in [1, 255]. Reserved slots are indexed from 0 to n-1.
// Room for 8 flags below ...
static const uintptr_t JSCLASS_RESERVED_SLOTS_SHIFT = 8;
// ... and 16 above this field.
static const uint32_t JSCLASS_RESERVED_SLOTS_WIDTH = 8;
static const uint32_t JSCLASS_RESERVED_SLOTS_MASK =
static constexpr uint32_t JSCLASS_HAS_RESERVED_SLOTS(uint32_t n) {
static constexpr uint32_t JSCLASS_HIGH_FLAGS_SHIFT =
static const uint32_t JSCLASS_INTERNAL_FLAG1 =
static const uint32_t JSCLASS_IS_GLOBAL = 1 << (JSCLASS_HIGH_FLAGS_SHIFT + 1);
static const uint32_t JSCLASS_INTERNAL_FLAG2 =
static const uint32_t JSCLASS_IS_PROXY = 1 << (JSCLASS_HIGH_FLAGS_SHIFT + 3);
static const uint32_t JSCLASS_SKIP_NURSERY_FINALIZE =
// Reserved for embeddings.
static const uint32_t JSCLASS_USERBIT2 = 1 << (JSCLASS_HIGH_FLAGS_SHIFT + 5);
static const uint32_t JSCLASS_USERBIT3 = 1 << (JSCLASS_HIGH_FLAGS_SHIFT + 6);
static const uint32_t JSCLASS_BACKGROUND_FINALIZE =
static const uint32_t JSCLASS_FOREGROUND_FINALIZE =
// Bits 25 through 31 are reserved for the CACHED_PROTO_KEY mechanism, see
// below.
// ECMA-262 requires that most constructors used internally create objects
// with "the original Foo.prototype value" as their [[Prototype]] (__proto__)
// member initial value. The "original ... value" verbiage is there because
// in ECMA-262, global properties naming class objects are read/write and
// deleteable, for the most part.
// Implementing this efficiently requires that global objects have classes
// with the following flags. Failure to use JSCLASS_GLOBAL_FLAGS was
// previously allowed, but is now an ES5 violation and thus unsupported.
// JSCLASS_GLOBAL_APPLICATION_SLOTS is the number of slots reserved at
// the beginning of every global object's slots for use by the
// application.
static const uint32_t JSCLASS_GLOBAL_APPLICATION_SLOTS = 5;
static const uint32_t JSCLASS_GLOBAL_SLOT_COUNT =
static constexpr uint32_t JSCLASS_GLOBAL_FLAGS_WITH_SLOTS(uint32_t n) {
static constexpr uint32_t JSCLASS_GLOBAL_FLAGS =
// Fast access to the original value of each standard class's prototype.
static const uint32_t JSCLASS_CACHED_PROTO_MASK =
static_assert(JSProto_LIMIT <= (JSCLASS_CACHED_PROTO_MASK + 1),
"JSProtoKey must not exceed the maximum cacheable proto-mask");
static constexpr uint32_t JSCLASS_HAS_CACHED_PROTO(JSProtoKey key) {
return uint32_t(key) << JSCLASS_CACHED_PROTO_SHIFT;
struct MOZ_STATIC_CLASS JSClassOps {
/* Function pointer members (may be null). */
JSAddPropertyOp addProperty;
JSDeletePropertyOp delProperty;
JSEnumerateOp enumerate;
JSNewEnumerateOp newEnumerate;
JSResolveOp resolve;
JSMayResolveOp mayResolve;
JSFinalizeOp finalize;
JSNative call;
JSNative construct;
JSTraceOp trace;
static constexpr const JSClassOps* JS_NULL_CLASS_OPS = nullptr;
// Note: This is a MOZ_STATIC_CLASS, as having a non-static JSClass
// can lead to bizarre behaviour, however the annotation
// is at the bottom to handle some incompatibility with GCC
// annotation processing.
struct alignas(js::gc::JSClassAlignBytes) JSClass {
const char* name;
uint32_t flags;
const JSClassOps* cOps;
const js::ClassSpec* spec;
const js::ClassExtension* ext;
const js::ObjectOps* oOps;
// Public accessors:
JSAddPropertyOp getAddProperty() const {
return cOps ? cOps->addProperty : nullptr;
JSDeletePropertyOp getDelProperty() const {
return cOps ? cOps->delProperty : nullptr;
JSEnumerateOp getEnumerate() const {
return cOps ? cOps->enumerate : nullptr;
JSNewEnumerateOp getNewEnumerate() const {
return cOps ? cOps->newEnumerate : nullptr;
JSResolveOp getResolve() const { return cOps ? cOps->resolve : nullptr; }
JSMayResolveOp getMayResolve() const {
return cOps ? cOps->mayResolve : nullptr;
JSNative getCall() const { return cOps ? cOps->call : nullptr; }
JSNative getConstruct() const { return cOps ? cOps->construct : nullptr; }
bool hasFinalize() const { return cOps && cOps->finalize; }
bool hasTrace() const { return cOps && cOps->trace; }
bool isTrace(JSTraceOp trace) const { return cOps && cOps->trace == trace; }
// The special treatment of |finalize| and |trace| is necessary because if we
// assign either of those hooks to a local variable and then call it -- as is
// done with the other hooks -- the GC hazard analysis gets confused.
void doFinalize(JS::GCContext* gcx, JSObject* obj) const {
MOZ_ASSERT(cOps && cOps->finalize);
cOps->finalize(gcx, obj);
void doTrace(JSTracer* trc, JSObject* obj) const {
MOZ_ASSERT(cOps && cOps->trace);
cOps->trace(trc, obj);
* Objects of this class aren't native objects. They don't have Shapes that
* describe their properties and layout. Classes using this flag must
* provide their own property behavior, either by being proxy classes (do
* this) or by overriding all the ObjectOps except getElements
* (don't do this).
static const uint32_t NON_NATIVE = JSCLASS_INTERNAL_FLAG2;
// A JSObject created from a JSClass extends from one of:
// - js::NativeObject
// - js::ProxyObject
// While it is possible to introduce new families of objects, it is strongly
// discouraged. The JITs would be entirely unable to optimize them and testing
// coverage is low. The existing NativeObject and ProxyObject are extremely
// flexible and are able to represent the entire Gecko embedding requirements.
// NOTE: Internal to SpiderMonkey, there is an experimental js::TypedObject
// object family for future WASM features.
bool isNativeObject() const { return !(flags & NON_NATIVE); }
bool isProxyObject() const { return flags & JSCLASS_IS_PROXY; }
bool emulatesUndefined() const { return flags & JSCLASS_EMULATES_UNDEFINED; }
bool isJSFunction() const {
return this == js::FunctionClassPtr || this == js::FunctionExtendedClassPtr;
bool nonProxyCallable() const {
return isJSFunction() || getCall();
bool isGlobal() const { return flags & JSCLASS_IS_GLOBAL; }
bool isDOMClass() const { return flags & JSCLASS_IS_DOMJSCLASS; }
bool shouldDelayMetadataBuilder() const {
bool isWrappedNative() const { return flags & JSCLASS_IS_WRAPPED_NATIVE; }
bool slot0IsISupports() const { return flags & JSCLASS_SLOT0_IS_NSISUPPORTS; }
static size_t offsetOfFlags() { return offsetof(JSClass, flags); }
// Internal / friend API accessors:
bool specDefined() const { return spec ? spec->defined() : false; }
JSProtoKey specInheritanceProtoKey() const {
return spec ? spec->inheritanceProtoKey() : JSProto_Null;
bool specShouldDefineConstructor() const {
return spec ? spec->shouldDefineConstructor() : true;
js::ClassObjectCreationOp specCreateConstructorHook() const {
return spec ? spec->createConstructor : nullptr;
js::ClassObjectCreationOp specCreatePrototypeHook() const {
return spec ? spec->createPrototype : nullptr;
const JSFunctionSpec* specConstructorFunctions() const {
return spec ? spec->constructorFunctions : nullptr;
const JSPropertySpec* specConstructorProperties() const {
return spec ? spec->constructorProperties : nullptr;
const JSFunctionSpec* specPrototypeFunctions() const {
return spec ? spec->prototypeFunctions : nullptr;
const JSPropertySpec* specPrototypeProperties() const {
return spec ? spec->prototypeProperties : nullptr;
js::FinishClassInitOp specFinishInitHook() const {
return spec ? spec->finishInit : nullptr;
JSObjectMovedOp extObjectMovedOp() const {
return ext ? ext->objectMovedOp : nullptr;
js::LookupPropertyOp getOpsLookupProperty() const {
return oOps ? oOps->lookupProperty : nullptr;
js::DefinePropertyOp getOpsDefineProperty() const {
return oOps ? oOps->defineProperty : nullptr;
js::HasPropertyOp getOpsHasProperty() const {
return oOps ? oOps->hasProperty : nullptr;
js::GetPropertyOp getOpsGetProperty() const {
return oOps ? oOps->getProperty : nullptr;
js::SetPropertyOp getOpsSetProperty() const {
return oOps ? oOps->setProperty : nullptr;
js::GetOwnPropertyOp getOpsGetOwnPropertyDescriptor() const {
return oOps ? oOps->getOwnPropertyDescriptor : nullptr;
js::DeletePropertyOp getOpsDeleteProperty() const {
return oOps ? oOps->deleteProperty : nullptr;
js::GetElementsOp getOpsGetElements() const {
return oOps ? oOps->getElements : nullptr;
JSFunToStringOp getOpsFunToString() const {
return oOps ? oOps->funToString : nullptr;
static constexpr uint32_t JSCLASS_RESERVED_SLOTS(const JSClass* clasp) {
return (clasp->flags >> JSCLASS_RESERVED_SLOTS_SHIFT) &
static constexpr bool JSCLASS_HAS_GLOBAL_FLAG_AND_SLOTS(const JSClass* clasp) {
return (clasp->flags & JSCLASS_IS_GLOBAL) &&
static constexpr JSProtoKey JSCLASS_CACHED_PROTO_KEY(const JSClass* clasp) {
return JSProtoKey((clasp->flags >> JSCLASS_CACHED_PROTO_SHIFT) &
namespace js {
* Enumeration describing possible values of the [[Class]] internal property
* value of objects.
enum class ESClass {
Function, // Note: Only JSFunction objects.
/** None of the above. */
/* Fills |vp| with the unboxed value for boxed types, or undefined otherwise. */
bool Unbox(JSContext* cx, JS::HandleObject obj, JS::MutableHandleValue vp);
// Classes with JSCLASS_SKIP_NURSERY_FINALIZE or Wrapper classes with
// CROSS_COMPARTMENT flags will not have their finalizer called if they are
// nursery allocated and not promoted to the tenured heap. The finalizers for
// these classes must do nothing except free data which was allocated via
// Nursery::allocateBuffer.
inline bool CanNurseryAllocateFinalizedClass(const JSClass* const clasp) {
return clasp->flags & JSCLASS_SKIP_NURSERY_FINALIZE;
#ifdef DEBUG
JS_PUBLIC_API bool HasObjectMovedOp(JSObject* obj);
} /* namespace js */
#endif /* js_Class_h */