JSClass.flags 编辑

JSCLASS_HAS_PRIVATE

This class uses private data. If this flag is set, each instance of the class has a field for private data. The field can be accessed using JS_GetPrivate and JS_SetPrivate.

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JSCLASS_PRIVATE_IS_NSISUPPORTS

Mozilla extension. The private field of each object of this class points to an XPCOM object (see nsISupports). This is only meaningful if SpiderMonkey is built with XPConnect and the JSCLASS_HAS_PRIVATE flag is also set.

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JSCLASS_IS_DOMJSCLASS

Added in SpiderMonkey 17 Objects are DOM.

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Added in SpiderMonkey 24 Causes objects which have this class to emulate undefined in certain circumstances.  An object obj that emulates undefined behaves like any other object, except in the following ways:

• typeof obj === "undefined"
• obj converts to false when obj is converted to a boolean when used in boolean contexts (if conditions, loop continuation/termination conditions [for/while/do { } while], the condition in a ternary ?: expression, and so on)
• (obj == undefined) is true, and (obj != undefined) is false
• (obj == null) is true, and (obj != null) is false

== and != comparisons to values other than null or undefined (including to an object that emulates undefined) are unaffected by this flag.  Strict equality (=== and !==) comparisons are also unaffected by this flag.

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JSCLASS_HAS_RESERVED_SLOTS(n)

Indicates that instances of this class have n reserved slots. n is an integer in the range [0..255]. The slots initially contain unspecified valid jsval values. They can be accessed using JS_GetReservedSlot and JS_SetReservedSlot.

(The JSClass.reserveSlots hook also allocates reserved slots to objects.)

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JSCLASS_GLOBAL_FLAGS

This flag is only relevant for the class of an object that is used as a global object. (ECMAScript specifies a single global object, but in SpiderMonkey the global object is the last object in the scope chain, which can be different objects at different times. This is actually quite subtle. JS_ExecuteScript and similar APIs set the global object for the code they execute. JS_SetGlobalObject sets an object which is sometimes used as the global object, as a last resort.)

Enable standard ECMAScript behavior for setting the prototype of certain objects, such as Function objects. If the global object does not have this flag, then scripts may cause nonstandard behavior by replacing standard constructors or prototypes (such as Function.prototype.)

Objects that can end up with the wrong prototype object, if this flag is not present, include: arguments objects (ECMA 262-3 §10.1.8 specifies "the original Object prototype"), Function objects (ECMA 262-3 §13.2 specifies "the original Function prototype"), and objects created by many standard constructors (ECMA 262-3 §15.4.2.1 and others).

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Objects of this class must be finalized on the main thread. 

If this class has a finalizer that makes use of state shared with the main thread then this option must be specified.  It is always safe to specify this option.

One of JSCLASS_FOREGROUND_FINALIZE and JSCLASS_BACKGROUND_FINALIZE must be specified.

It is safe to finalize objects of this class on a background thread.

If this class has a finalizer that can be safely run concurrently with the main thread then this option can be specified.  It results in finalization work being offloaded to another thread which improves performance.

One of JSCLASS_FOREGROUND_FINALIZE and JSCLASS_BACKGROUND_FINALIZE must be specified.

JSCLASS_NEW_ENUMERATE

JSCLASS_NEW_RESOLVE

JSCLASS_SHARE_ALL_PROPERTIES

JSCLASS_NEW_RESOLVE_GETS_START

JSCLASS_CONSTRUCT_PROTOTYPE

JSCLASS_IS_EXTENDED

JSCLASS_MARK_IS_TRACE