[领域]javascript hacking guide 第5部分

struct JSObject {

    JSObjectMap *map;

    jsval       *slots;

};

struct JSObjectMap {

    jsrefcount  nrefs;          /* count of all referencing objects */

    JSObjectOps *ops;           /* high level object operation vtable */

    uint32      nslots;         /* length of obj->slots vector */

    uint32      freeslot;       /* index of next free obj->slots element */

};

var obj = new Object();

obj.a = 5;

struct JSObjectOps {

    /* Mandatory non-null function pointer members. */

    JSNewObjectMapOp    newObjectMap;

    JSObjectMapOp       destroyObjectMap;

    JSLookupPropOp      lookupProperty;

    JSDefinePropOp      defineProperty;

    JSPropertyIdOp      getProperty;

    JSPropertyIdOp      setProperty;

    JSAttributesOp      getAttributes;

    JSAttributesOp      setAttributes;

    JSPropertyIdOp      deleteProperty;

    JSConvertOp         defaultValue;

    JSNewEnumerateOp    enumerate;

    JSCheckAccessIdOp   checkAccess;

    /* Optionally non-null members start here. */

    JSObjectOp          thisObject;

    JSPropertyRefOp     dropProperty;

    JSNative            call;

    JSNative            construct;

    JSXDRObjectOp       xdrObject;

    JSHasInstanceOp     hasInstance;

    JSSetObjectSlotOp   setProto;

    JSSetObjectSlotOp   setParent;

    JSMarkOp            mark;

    JSFinalizeOp        clear;

    JSGetRequiredSlotOp getRequiredSlot;

    JSSetRequiredSlotOp setRequiredSlot;

};

/*

     * Share proto's map only if it has the same JSObjectOps, and only if

     * proto's class has the same private and reserved slots as obj's map

     * and class have.  We assume that if prototype and object are of the

     * same class, they always have the same number of computed reserved

     * slots (returned via clasp->reserveSlots); otherwise, prototype and

     * object classes must have the same (null or not) reserveSlots hook.

     */

    if (proto &&

        (map = proto->map)->ops == ops &&

        ((protoclasp = OBJ_GET_CLASS(cx, proto)) == clasp ||

         (!((protoclasp->flags ^ clasp->flags) &

            (JSCLASS_HAS_PRIVATE |

             (JSCLASS_RESERVED_SLOTS_MASK << JSCLASS_RESERVED_SLOTS_SHIFT))) &&

          protoclasp->reserveSlots == clasp->reserveSlots)))

    {

        /*

         * Default parent to the parent of the prototype, which was set from

         * the parent of the prototype's constructor.

         */

        if (!parent)

            parent = OBJ_GET_PARENT(cx, proto);

        /* Share the given prototype's map. */

        obj->map = js_HoldObjectMap(cx, map);

        /* Ensure that obj starts with the minimum slots for clasp. */

        nslots = JS_INITIAL_NSLOTS;

    } else {

        /* Leave parent alone.  Allocate a new map for obj. */

        map = ops->newObjectMap(cx, 1, ops, clasp, obj);

        if (!map)

            goto bad;

        obj->map = map;

        /* Let ops->newObjectMap set nslots so as to reserve slots. */

        nslots = map->nslots;

    }

/* Allocate a slots vector, with a -1'st element telling its length. */

    newslots = AllocSlots(cx, NULL, nslots);

    if (!newslots) {

        js_DropObjectMap(cx, obj->map, obj);

        obj->map = NULL;

        goto bad;

    }

    /* Set the proto, parent, and class properties. */

    newslots[JSSLOT_PROTO] = OBJECT_TO_JSVAL(proto);

    newslots[JSSLOT_PARENT] = OBJECT_TO_JSVAL(parent);

    newslots[JSSLOT_CLASS] = PRIVATE_TO_JSVAL(clasp);

    /* Clear above JSSLOT_CLASS so the GC doesn't load uninitialized memory. */

    for (i = JSSLOT_CLASS + 1; i < nslots; i++)

        newslots[i] = JSVAL_VOID;

    /* Store newslots after initializing all of 'em, just in case. */

    obj->slots = newslots;