duktape-1.5.2/src-separate/duk_hobject_enum.c

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/*
 *  Hobject enumeration support.
 *
 *  Creates an internal enumeration state object to be used e.g. with for-in
 *  enumeration.  The state object contains a snapshot of target object keys
 *  and internal control state for enumeration.  Enumerator flags allow caller
 *  to e.g. request internal/non-enumerable properties, and to enumerate only
 *  "own" properties.
 *
 *  Also creates the result value for e.g. Object.keys() based on the same
 *  internal structure.
 *
 *  This snapshot-based enumeration approach is used to simplify enumeration:
 *  non-snapshot-based approaches are difficult to reconcile with mutating
 *  the enumeration target, running multiple long-lived enumerators at the
 *  same time, garbage collection details, etc.  The downside is that the
 *  enumerator object is memory inefficient especially for iterating arrays.
 */
 
#include "duk_internal.h"
 
/* XXX: identify enumeration target with an object index (not top of stack) */
 
/* must match exactly the number of internal properties inserted to enumerator */
#define DUK__ENUM_START_INDEX  2
 
DUK_LOCAL const duk_uint16_t duk__bufferobject_virtual_props[] = {
    DUK_STRIDX_LENGTH,
    DUK_STRIDX_BYTE_LENGTH,
    DUK_STRIDX_BYTE_OFFSET,
    DUK_STRIDX_BYTES_PER_ELEMENT
};
 
/*
 *  Helper to sort array index keys.  The keys are in the enumeration object
 *  entry part, starting from DUK__ENUM_START_INDEX, and the entry part is dense.
 *
 *  We use insertion sort because it is simple (leading to compact code,)
 *  works nicely in-place, and minimizes operations if data is already sorted
 *  or nearly sorted (which is a very common case here).  It also minimizes
 *  the use of element comparisons in general.  This is nice because element
 *  comparisons here involve re-parsing the string keys into numbers each
 *  time, which is naturally very expensive.
 *
 *  Note that the entry part values are all "true", e.g.
 *
 *    "1" -> true, "3" -> true, "2" -> true
 *
 *  so it suffices to only work in the key part without exchanging any keys,
 *  simplifying the sort.
 *
 *  http://en.wikipedia.org/wiki/Insertion_sort
 *
 *  (Compiles to about 160 bytes now as a stand-alone function.)
 */
 
DUK_LOCAL void duk__sort_array_indices(duk_hthread *thr, duk_hobject *h_obj) {
    duk_hstring **keys;
    duk_hstring **p_curr, **p_insert, **p_end;
    duk_hstring *h_curr;
    duk_uarridx_t val_highest, val_curr, val_insert;
 
    DUK_ASSERT(h_obj != NULL);
    DUK_ASSERT(DUK_HOBJECT_GET_ENEXT(h_obj) >= 2);  /* control props */
    DUK_UNREF(thr);
 
    if (DUK_HOBJECT_GET_ENEXT(h_obj) <= 1 + DUK__ENUM_START_INDEX) {
        return;
    }
 
    keys = DUK_HOBJECT_E_GET_KEY_BASE(thr->heap, h_obj);
    p_end = keys + DUK_HOBJECT_GET_ENEXT(h_obj);
    keys += DUK__ENUM_START_INDEX;
 
    DUK_DDD(DUK_DDDPRINT("keys=%p, p_end=%p (after skipping enum props)",
                         (void *) keys, (void *) p_end));
 
#ifdef DUK_USE_DDDPRINT
    {
        duk_uint_fast32_t i;
        for (i = 0; i < (duk_uint_fast32_t) DUK_HOBJECT_GET_ENEXT(h_obj); i++) {
            DUK_DDD(DUK_DDDPRINT("initial: %ld %p -> %!O",
                                 (long) i,
                                 (void *) DUK_HOBJECT_E_GET_KEY_PTR(thr->heap, h_obj, i),
                                 (duk_heaphdr *) DUK_HOBJECT_E_GET_KEY(thr->heap, h_obj, i)));
        }
    }
#endif
 
    val_highest = DUK_HSTRING_GET_ARRIDX_SLOW(keys[0]);
    for (p_curr = keys + 1; p_curr < p_end; p_curr++) {
        DUK_ASSERT(*p_curr != NULL);
        val_curr = DUK_HSTRING_GET_ARRIDX_SLOW(*p_curr);
 
        if (val_curr >= val_highest) {
            DUK_DDD(DUK_DDDPRINT("p_curr=%p, p_end=%p, val_highest=%ld, val_curr=%ld -> "
                                 "already in correct order, next",
                                 (void *) p_curr, (void *) p_end, (long) val_highest, (long) val_curr));
            val_highest = val_curr;
            continue;
        }
 
        DUK_DDD(DUK_DDDPRINT("p_curr=%p, p_end=%p, val_highest=%ld, val_curr=%ld -> "
                             "needs to be inserted",
                             (void *) p_curr, (void *) p_end, (long) val_highest, (long) val_curr));
 
        /* Needs to be inserted; scan backwards, since we optimize
         * for the case where elements are nearly in order.
         */
 
        p_insert = p_curr - 1;
        for (;;) {
            val_insert = DUK_HSTRING_GET_ARRIDX_SLOW(*p_insert);
            if (val_insert < val_curr) {
                DUK_DDD(DUK_DDDPRINT("p_insert=%p, val_insert=%ld, val_curr=%ld -> insert after this",
                                     (void *) p_insert, (long) val_insert, (long) val_curr));
                p_insert++;
                break;
            }
            if (p_insert == keys) {
                DUK_DDD(DUK_DDDPRINT("p_insert=%p -> out of keys, insert to beginning", (void *) p_insert));
                break;
            }
            DUK_DDD(DUK_DDDPRINT("p_insert=%p, val_insert=%ld, val_curr=%ld -> search backwards",
                                 (void *) p_insert, (long) val_insert, (long) val_curr));
            p_insert--;
        }
 
        DUK_DDD(DUK_DDDPRINT("final p_insert=%p", (void *) p_insert));
 
        /*        .-- p_insert   .-- p_curr
         *        v              v
         *  | ... | insert | ... | curr
         */
 
        h_curr = *p_curr;
        DUK_DDD(DUK_DDDPRINT("memmove: dest=%p, src=%p, size=%ld, h_curr=%p",
                             (void *) (p_insert + 1), (void *) p_insert,
                             (long) (p_curr - p_insert), (void *) h_curr));
 
        DUK_MEMMOVE((void *) (p_insert + 1),
                    (const void *) p_insert,
                    (size_t) ((p_curr - p_insert) * sizeof(duk_hstring *)));
        *p_insert = h_curr;
        /* keep val_highest */
    }
 
#ifdef DUK_USE_DDDPRINT
    {
        duk_uint_fast32_t i;
        for (i = 0; i < (duk_uint_fast32_t) DUK_HOBJECT_GET_ENEXT(h_obj); i++) {
            DUK_DDD(DUK_DDDPRINT("final: %ld %p -> %!O",
                                 (long) i,
                                 (void *) DUK_HOBJECT_E_GET_KEY_PTR(thr->heap, h_obj, i),
                                 (duk_heaphdr *) DUK_HOBJECT_E_GET_KEY(thr->heap, h_obj, i)));
        }
    }
#endif
}
 
/*
 *  Create an internal enumerator object E, which has its keys ordered
 *  to match desired enumeration ordering.  Also initialize internal control
 *  properties for enumeration.
 *
 *  Note: if an array was used to hold enumeration keys instead, an array
 *  scan would be needed to eliminate duplicates found in the prototype chain.
 */
 
DUK_INTERNAL void duk_hobject_enumerator_create(duk_context *ctx, duk_small_uint_t enum_flags) {
    duk_hthread *thr = (duk_hthread *) ctx;
    duk_hobject *enum_target;
    duk_hobject *curr;
    duk_hobject *res;
#if defined(DUK_USE_ES6_PROXY)
    duk_hobject *h_proxy_target;
    duk_hobject *h_proxy_handler;
    duk_hobject *h_trap_result;
#endif
    duk_uint_fast32_t i, len;  /* used for array, stack, and entry indices */
 
    DUK_ASSERT(ctx != NULL);
 
    DUK_DDD(DUK_DDDPRINT("create enumerator, stack top: %ld", (long) duk_get_top(ctx)));
 
    enum_target = duk_require_hobject(ctx, -1);
    DUK_ASSERT(enum_target != NULL);
 
    duk_push_object_internal(ctx);
    res = duk_require_hobject(ctx, -1);
 
    DUK_DDD(DUK_DDDPRINT("created internal object"));
 
    /* [enum_target res] */
 
    /* Target must be stored so that we can recheck whether or not
     * keys still exist when we enumerate.  This is not done if the
     * enumeration result comes from a proxy trap as there is no
     * real object to check against.
     */
    duk_push_hobject(ctx, enum_target);
    duk_put_prop_stridx(ctx, -2, DUK_STRIDX_INT_TARGET);
 
    /* Initialize index so that we skip internal control keys. */
    duk_push_int(ctx, DUK__ENUM_START_INDEX);
    duk_put_prop_stridx(ctx, -2, DUK_STRIDX_INT_NEXT);
 
    /*
     *  Proxy object handling
     */
 
#if defined(DUK_USE_ES6_PROXY)
    if (DUK_LIKELY((enum_flags & DUK_ENUM_NO_PROXY_BEHAVIOR) != 0)) {
        goto skip_proxy;
    }
    if (DUK_LIKELY(!duk_hobject_proxy_check(thr,
                                            enum_target,
                                            &h_proxy_target,
                                            &h_proxy_handler))) {
        goto skip_proxy;
    }
 
    DUK_DDD(DUK_DDDPRINT("proxy enumeration"));
    duk_push_hobject(ctx, h_proxy_handler);
    if (!duk_get_prop_stridx(ctx, -1, DUK_STRIDX_ENUMERATE)) {
        /* No need to replace the 'enum_target' value in stack, only the
         * enum_target reference.  This also ensures that the original
         * enum target is reachable, which keeps the proxy and the proxy
         * target reachable.  We do need to replace the internal _Target.
         */
        DUK_DDD(DUK_DDDPRINT("no enumerate trap, enumerate proxy target instead"));
        DUK_DDD(DUK_DDDPRINT("h_proxy_target=%!O", (duk_heaphdr *) h_proxy_target));
        enum_target = h_proxy_target;
 
        duk_push_hobject(ctx, enum_target);  /* -> [ ... enum_target res handler undefined target ] */
        duk_put_prop_stridx(ctx, -4, DUK_STRIDX_INT_TARGET);
 
        duk_pop_2(ctx);  /* -> [ ... enum_target res ] */
        goto skip_proxy;
    }
 
    /* [ ... enum_target res handler trap ] */
    duk_insert(ctx, -2);
    duk_push_hobject(ctx, h_proxy_target);    /* -> [ ... enum_target res trap handler target ] */
    duk_call_method(ctx, 1 /*nargs*/);        /* -> [ ... enum_target res trap_result ] */
    h_trap_result = duk_require_hobject(ctx, -1);
    DUK_UNREF(h_trap_result);
 
    /* Copy trap result keys into the enumerator object. */
    len = (duk_uint_fast32_t) duk_get_length(ctx, -1);
    for (i = 0; i < len; i++) {
        /* XXX: not sure what the correct semantic details are here,
         * e.g. handling of missing values (gaps), handling of non-array
         * trap results, etc.
         *
         * For keys, we simply skip non-string keys which seems to be
         * consistent with how e.g. Object.keys() will process proxy trap
         * results (ES6, Section 19.1.2.14).
         */
        if (duk_get_prop_index(ctx, -1, i) && duk_is_string(ctx, -1)) {
            /* [ ... enum_target res trap_result val ] */
            duk_push_true(ctx);
            /* [ ... enum_target res trap_result val true ] */
            duk_put_prop(ctx, -4);
        } else {
            duk_pop(ctx);
        }
    }
    /* [ ... enum_target res trap_result ] */
    duk_pop(ctx);
    duk_remove(ctx, -2);
 
    /* [ ... res ] */
 
    /* The internal _Target property is kept pointing to the original
     * enumeration target (the proxy object), so that the enumerator
     * 'next' operation can read property values if so requested.  The
     * fact that the _Target is a proxy disables key existence check
     * during enumeration.
     */
    DUK_DDD(DUK_DDDPRINT("proxy enumeration, final res: %!O", (duk_heaphdr *) res));
    goto compact_and_return;
 
 skip_proxy:
#endif  /* DUK_USE_ES6_PROXY */
 
    curr = enum_target;
    while (curr) {
        /*
         *  Virtual properties.
         *
         *  String and buffer indices are virtual and always enumerable,
         *  'length' is virtual and non-enumerable.  Array and arguments
         *  object props have special behavior but are concrete.
         */
 
        if (DUK_HOBJECT_HAS_EXOTIC_STRINGOBJ(curr) ||
            DUK_HOBJECT_IS_BUFFEROBJECT(curr)) {
            /* String and buffer enumeration behavior is identical now,
             * so use shared handler.
             */
            if (DUK_HOBJECT_HAS_EXOTIC_STRINGOBJ(curr)) {
                duk_hstring *h_val;
                h_val = duk_hobject_get_internal_value_string(thr->heap, curr);
                DUK_ASSERT(h_val != NULL);  /* string objects must not created without internal value */
                len = (duk_uint_fast32_t) DUK_HSTRING_GET_CHARLEN(h_val);
            } else {
                duk_hbufferobject *h_bufobj;
                DUK_ASSERT(DUK_HOBJECT_IS_BUFFEROBJECT(curr));
                h_bufobj = (duk_hbufferobject *) curr;
                if (h_bufobj == NULL) {
                    /* Neutered buffer, zero length seems
                     * like good behavior here.
                     */
                    len = 0;
                } else {
                    /* There's intentionally no check for
                     * current underlying buffer length.
                     */
                    len = (duk_uint_fast32_t) (h_bufobj->length >> h_bufobj->shift);
                }
            }
 
            for (i = 0; i < len; i++) {
                duk_hstring *k;
 
                k = duk_heap_string_intern_u32_checked(thr, i);
                DUK_ASSERT(k);
                duk_push_hstring(ctx, k);
                duk_push_true(ctx);
 
                /* [enum_target res key true] */
                duk_put_prop(ctx, -3);
 
                /* [enum_target res] */
            }
 
            /* 'length' and other virtual properties are not
             * enumerable, but are included if non-enumerable
             * properties are requested.
             */
 
            if (enum_flags & DUK_ENUM_INCLUDE_NONENUMERABLE) {
                duk_uint_fast32_t n;
 
                if (DUK_HOBJECT_IS_BUFFEROBJECT(curr)) {
                    n = sizeof(duk__bufferobject_virtual_props) / sizeof(duk_uint16_t);
                } else {
                    DUK_ASSERT(DUK_HOBJECT_HAS_EXOTIC_STRINGOBJ(curr));
                    DUK_ASSERT(duk__bufferobject_virtual_props[0] == DUK_STRIDX_LENGTH);
                    n = 1;  /* only 'length' */
                }
 
                for (i = 0; i < n; i++) {
                    duk_push_hstring_stridx(ctx, duk__bufferobject_virtual_props[i]);
                    duk_push_true(ctx);
                    duk_put_prop(ctx, -3);
                }
 
            }
        } else if (DUK_HOBJECT_HAS_EXOTIC_DUKFUNC(curr)) {
            if (enum_flags & DUK_ENUM_INCLUDE_NONENUMERABLE) {
                duk_push_hstring_stridx(ctx, DUK_STRIDX_LENGTH);
                duk_push_true(ctx);
                duk_put_prop(ctx, -3);
            }
        }
 
        /*
         *  Array part
         *
         *  Note: ordering between array and entry part must match 'abandon array'
         *  behavior in duk_hobject_props.c: key order after an array is abandoned
         *  must be the same.
         */
 
        for (i = 0; i < (duk_uint_fast32_t) DUK_HOBJECT_GET_ASIZE(curr); i++) {
            duk_hstring *k;
            duk_tval *tv;
 
            tv = DUK_HOBJECT_A_GET_VALUE_PTR(thr->heap, curr, i);
            if (DUK_TVAL_IS_UNUSED(tv)) {
                continue;
            }
            k = duk_heap_string_intern_u32_checked(thr, i);
            DUK_ASSERT(k);
 
            duk_push_hstring(ctx, k);
            duk_push_true(ctx);
 
            /* [enum_target res key true] */
            duk_put_prop(ctx, -3);
 
            /* [enum_target res] */
        }
 
        /*
         *  Entries part
         */
 
        for (i = 0; i < (duk_uint_fast32_t) DUK_HOBJECT_GET_ENEXT(curr); i++) {
            duk_hstring *k;
 
            k = DUK_HOBJECT_E_GET_KEY(thr->heap, curr, i);
            if (!k) {
                continue;
            }
            if (!DUK_HOBJECT_E_SLOT_IS_ENUMERABLE(thr->heap, curr, i) &&
                !(enum_flags & DUK_ENUM_INCLUDE_NONENUMERABLE)) {
                continue;
            }
            if (DUK_HSTRING_HAS_INTERNAL(k) &&
                !(enum_flags & DUK_ENUM_INCLUDE_INTERNAL)) {
                continue;
            }
            if ((enum_flags & DUK_ENUM_ARRAY_INDICES_ONLY) &&
                (DUK_HSTRING_GET_ARRIDX_SLOW(k) == DUK_HSTRING_NO_ARRAY_INDEX)) {
                continue;
            }
 
            DUK_ASSERT(DUK_HOBJECT_E_SLOT_IS_ACCESSOR(thr->heap, curr, i) ||
                       !DUK_TVAL_IS_UNUSED(&DUK_HOBJECT_E_GET_VALUE_PTR(thr->heap, curr, i)->v));
 
            duk_push_hstring(ctx, k);
            duk_push_true(ctx);
 
            /* [enum_target res key true] */
            duk_put_prop(ctx, -3);
 
            /* [enum_target res] */
        }
 
        if (enum_flags & DUK_ENUM_OWN_PROPERTIES_ONLY) {
            break;
        }
 
        curr = DUK_HOBJECT_GET_PROTOTYPE(thr->heap, curr);
    }
 
    /* [enum_target res] */
 
    duk_remove(ctx, -2);
 
    /* [res] */
 
    if ((enum_flags & (DUK_ENUM_ARRAY_INDICES_ONLY | DUK_ENUM_SORT_ARRAY_INDICES)) ==
                      (DUK_ENUM_ARRAY_INDICES_ONLY | DUK_ENUM_SORT_ARRAY_INDICES)) {
        /*
         *  Some E5/E5.1 algorithms require that array indices are iterated
         *  in a strictly ascending order.  This is the case for e.g.
         *  Array.prototype.forEach() and JSON.stringify() PropertyList
         *  handling.
         *
         *  To ensure this property for arrays with an array part (and
         *  arbitrary objects too, since e.g. forEach() can be applied
         *  to an array), the caller can request that we sort the keys
         *  here.
         */
 
        /* XXX: avoid this at least when enum_target is an Array, it has an
         * array part, and no ancestor properties were included?  Not worth
         * it for JSON, but maybe worth it for forEach().
         */
 
        /* XXX: may need a 'length' filter for forEach()
         */
        DUK_DDD(DUK_DDDPRINT("sort array indices by caller request"));
        duk__sort_array_indices(thr, res);
    }
 
#if defined(DUK_USE_ES6_PROXY)
 compact_and_return:
#endif
    /* compact; no need to seal because object is internal */
    duk_hobject_compact_props(thr, res);
 
    DUK_DDD(DUK_DDDPRINT("created enumerator object: %!iT", (duk_tval *) duk_get_tval(ctx, -1)));
}
 
/*
 *  Returns non-zero if a key and/or value was enumerated, and:
 *
 *   [enum] -> [key]        (get_value == 0)
 *   [enum] -> [key value]  (get_value == 1)
 *
 *  Returns zero without pushing anything on the stack otherwise.
 */
DUK_INTERNAL duk_bool_t duk_hobject_enumerator_next(duk_context *ctx, duk_bool_t get_value) {
    duk_hthread *thr = (duk_hthread *) ctx;
    duk_hobject *e;
    duk_hobject *enum_target;
    duk_hstring *res = NULL;
    duk_uint_fast32_t idx;
    duk_bool_t check_existence;
 
    DUK_ASSERT(ctx != NULL);
 
    /* [... enum] */
 
    e = duk_require_hobject(ctx, -1);
 
    /* XXX use get tval ptr, more efficient */
    duk_get_prop_stridx(ctx, -1, DUK_STRIDX_INT_NEXT);
    idx = (duk_uint_fast32_t) duk_require_uint(ctx, -1);
    duk_pop(ctx);
    DUK_DDD(DUK_DDDPRINT("enumeration: index is: %ld", (long) idx));
 
    /* Enumeration keys are checked against the enumeration target (to see
     * that they still exist).  In the proxy enumeration case _Target will
     * be the proxy, and checking key existence against the proxy is not
     * required (or sensible, as the keys may be fully virtual).
     */
    duk_get_prop_stridx(ctx, -1, DUK_STRIDX_INT_TARGET);
    enum_target = duk_require_hobject(ctx, -1);
    DUK_ASSERT(enum_target != NULL);
#if defined(DUK_USE_ES6_PROXY)
    check_existence = (!DUK_HOBJECT_HAS_EXOTIC_PROXYOBJ(enum_target));
#else
    check_existence = 1;
#endif
    duk_pop(ctx);  /* still reachable */
 
    DUK_DDD(DUK_DDDPRINT("getting next enum value, enum_target=%!iO, enumerator=%!iT",
                         (duk_heaphdr *) enum_target, (duk_tval *) duk_get_tval(ctx, -1)));
 
    /* no array part */
    for (;;) {
        duk_hstring *k;
 
        if (idx >= DUK_HOBJECT_GET_ENEXT(e)) {
            DUK_DDD(DUK_DDDPRINT("enumeration: ran out of elements"));
            break;
        }
 
        /* we know these because enum objects are internally created */
        k = DUK_HOBJECT_E_GET_KEY(thr->heap, e, idx);
        DUK_ASSERT(k != NULL);
        DUK_ASSERT(!DUK_HOBJECT_E_SLOT_IS_ACCESSOR(thr->heap, e, idx));
        DUK_ASSERT(!DUK_TVAL_IS_UNUSED(&DUK_HOBJECT_E_GET_VALUE(thr->heap, e, idx).v));
 
        idx++;
 
        /* recheck that the property still exists */
        if (check_existence && !duk_hobject_hasprop_raw(thr, enum_target, k)) {
            DUK_DDD(DUK_DDDPRINT("property deleted during enumeration, skip"));
            continue;
        }
 
        DUK_DDD(DUK_DDDPRINT("enumeration: found element, key: %!O", (duk_heaphdr *) k));
        res = k;
        break;
    }
 
    DUK_DDD(DUK_DDDPRINT("enumeration: updating next index to %ld", (long) idx));
 
    duk_push_u32(ctx, (duk_uint32_t) idx);
    duk_put_prop_stridx(ctx, -2, DUK_STRIDX_INT_NEXT);
 
    /* [... enum] */
 
    if (res) {
        duk_push_hstring(ctx, res);
        if (get_value) {
            duk_push_hobject(ctx, enum_target);
            duk_dup(ctx, -2);      /* -> [... enum key enum_target key] */
            duk_get_prop(ctx, -2); /* -> [... enum key enum_target val] */
            duk_remove(ctx, -2);   /* -> [... enum key val] */
            duk_remove(ctx, -3);   /* -> [... key val] */
        } else {
            duk_remove(ctx, -2);   /* -> [... key] */
        }
        return 1;
    } else {
        duk_pop(ctx);  /* -> [...] */
        return 0;
    }
}
 
/*
 *  Get enumerated keys in an Ecmascript array.  Matches Object.keys() behavior
 *  described in E5 Section 15.2.3.14.
 */
 
DUK_INTERNAL duk_ret_t duk_hobject_get_enumerated_keys(duk_context *ctx, duk_small_uint_t enum_flags) {
    duk_hthread *thr = (duk_hthread *) ctx;
    duk_hobject *e;
    duk_uint_fast32_t i;
    duk_uint_fast32_t idx;
 
    DUK_ASSERT(ctx != NULL);
    DUK_ASSERT(duk_get_hobject(ctx, -1) != NULL);
    DUK_UNREF(thr);
 
    /* Create a temporary enumerator to get the (non-duplicated) key list;
     * the enumerator state is initialized without being needed, but that
     * has little impact.
     */
 
    duk_hobject_enumerator_create(ctx, enum_flags);
    duk_push_array(ctx);
 
    /* [enum_target enum res] */
 
    e = duk_require_hobject(ctx, -2);
    DUK_ASSERT(e != NULL);
 
    idx = 0;
    for (i = DUK__ENUM_START_INDEX; i < (duk_uint_fast32_t) DUK_HOBJECT_GET_ENEXT(e); i++) {
        duk_hstring *k;
 
        k = DUK_HOBJECT_E_GET_KEY(thr->heap, e, i);
        DUK_ASSERT(k);  /* enumerator must have no keys deleted */
 
        /* [enum_target enum res] */
        duk_push_hstring(ctx, k);
        duk_put_prop_index(ctx, -2, idx);
        idx++;
    }
 
    /* [enum_target enum res] */
    duk_remove(ctx, -2);
 
    /* [enum_target res] */
 
    return 1;  /* return 1 to allow callers to tail call */
}