diff --git a/include/ant.h b/include/ant.h
index 5e4d8da..999a332 100644
--- a/include/ant.h
+++ b/include/ant.h
@@ -114,8 +114,8 @@ ant_value_t js_mksym_well_known(ant_t *, const char *desc);
 ant_value_t js_mkfun_meta(const ant_cfunc_meta_t *meta);
 ant_value_t js_mkfun_dyn(ant_cfunc_t fn);
 
-ant_value_t js_heavy_mkfun(ant_t *js, ant_value_t (*fn)(ant_t *, ant_value_t *, int), ant_value_t data);
-ant_value_t js_heavy_mkfun_native(ant_t *js, ant_value_t (*fn)(ant_t *, ant_value_t *, int), void *ptr, uint32_t tag);
+ant_value_t js_heavy_mkfun(ant_t *js, ant_value_t (*fn)(ant_params_t), ant_value_t data);
+ant_value_t js_heavy_mkfun_native(ant_t *js, ant_value_t (*fn)(ant_params_t), void *ptr, uint32_t tag);
 ant_value_t js_mkprop_fast(ant_t *js, ant_value_t obj, const char *key, size_t len, ant_value_t v);
 
 // TODO: deprecate
diff --git a/src/streams/codec.c b/src/streams/codec.c
index efe4974..754bd8c 100644
--- a/src/streams/codec.c
+++ b/src/streams/codec.c
@@ -86,9 +86,11 @@ static ant_value_t codec_flush_controller(ant_value_t *args, int nargs) {
 }
 
 static ant_value_t tes_transform(ant_t *js, ant_value_t *args, int nargs) {
-  ant_value_t wrapper = js_get_slot(js->current_func, SLOT_DATA);
+  tes_state_t *st = js_check_native_tag(js->current_func, TES_NATIVE_TAG)
+    ? (tes_state_t *)js_get_native_ptr(js->current_func)
+    : NULL;
   
-  tes_state_t *st = (tes_state_t *)js_get_native_ptr(wrapper);
+  if (!st) return js_mkerr_typed(js, JS_ERR_TYPE, "Invalid TextEncoderStream");
   ant_value_t ctrl_obj = codec_transform_controller(args, nargs);
   ant_value_t chunk = (nargs > 0) ? args[0] : js_mkundef();
   
@@ -171,8 +173,11 @@ static ant_value_t tes_transform(ant_t *js, ant_value_t *args, int nargs) {
 }
 
 static ant_value_t tes_flush(ant_t *js, ant_value_t *args, int nargs) {
-  ant_value_t wrapper = js_get_slot(js->current_func, SLOT_DATA);
-  tes_state_t *st = (tes_state_t *)js_get_native_ptr(wrapper);
+  tes_state_t *st = js_check_native_tag(js->current_func, TES_NATIVE_TAG)
+    ? (tes_state_t *)js_get_native_ptr(js->current_func)
+    : NULL;
+  
+  if (!st) return js_mkerr_typed(js, JS_ERR_TYPE, "Invalid TextEncoderStream");
   ant_value_t ctrl_obj = codec_flush_controller(args, nargs);
 
   if (st->pending_len > 0) {
@@ -220,12 +225,9 @@ static ant_value_t js_tes_ctor(ant_t *js, ant_value_t *args, int nargs) {
   js_set_native(obj, st, TES_NATIVE_TAG);
   js_set_finalizer(obj, tes_state_finalize);
 
-  ant_value_t wrapper = js_mkobj(js);
-  js_set_native(wrapper, st, TES_NATIVE_TAG);
-
   ant_value_t transformer = js_mkobj(js);
-  ant_value_t transform_fn = js_heavy_mkfun(js, tes_transform, wrapper);
-  ant_value_t flush_fn = js_heavy_mkfun(js, tes_flush, wrapper);
+  ant_value_t transform_fn = js_heavy_mkfun_native(js, tes_transform, st, TES_NATIVE_TAG);
+  ant_value_t flush_fn = js_heavy_mkfun_native(js, tes_flush, st, TES_NATIVE_TAG);
   js_set(js, transformer, "transform", transform_fn);
   js_set(js, transformer, "flush", flush_fn);
 
@@ -240,14 +242,16 @@ static ant_value_t js_tes_ctor(ant_t *js, ant_value_t *args, int nargs) {
 
   if (is_err(ts_obj)) { free(st); return ts_obj; }
   js_set_slot(obj, SLOT_ENTRIES, ts_obj);
-  js_set_slot(wrapper, SLOT_ENTRIES, ts_obj);
 
   return obj;
 }
 
 static ant_value_t tds_transform(ant_t *js, ant_value_t *args, int nargs) {
-  ant_value_t wrapper = js_get_slot(js->current_func, SLOT_DATA);
-  td_state_t *st = (td_state_t *)js_get_native_ptr(wrapper);
+  td_state_t *st = js_check_native_tag(js->current_func, TDS_NATIVE_TAG)
+    ? (td_state_t *)js_get_native_ptr(js->current_func)
+    : NULL;
+  
+  if (!st) return js_mkerr_typed(js, JS_ERR_TYPE, "Invalid TextDecoderStream");
   ant_value_t ctrl_obj = codec_transform_controller(args, nargs);
 
   ant_value_t chunk = (nargs > 0) ? args[0] : js_mkundef();
@@ -272,8 +276,11 @@ static ant_value_t tds_transform(ant_t *js, ant_value_t *args, int nargs) {
 }
 
 static ant_value_t tds_flush(ant_t *js, ant_value_t *args, int nargs) {
-  ant_value_t wrapper = js_get_slot(js->current_func, SLOT_DATA);
-  td_state_t *st = (td_state_t *)js_get_native_ptr(wrapper);
+  td_state_t *st = js_check_native_tag(js->current_func, TDS_NATIVE_TAG)
+    ? (td_state_t *)js_get_native_ptr(js->current_func)
+    : NULL;
+  
+  if (!st) return js_mkerr_typed(js, JS_ERR_TYPE, "Invalid TextDecoderStream");
   ant_value_t ctrl_obj = codec_flush_controller(args, nargs);
 
   ant_value_t result = td_decode(js, st, NULL, 0, false);
@@ -394,12 +401,10 @@ static ant_value_t js_tds_ctor(ant_t *js, ant_value_t *args, int nargs) {
   js_set_native(obj, st, TDS_NATIVE_TAG);
   js_set_finalizer(obj, tds_state_finalize);
 
-  ant_value_t wrapper = js_mkobj(js);
-  js_set_native(wrapper, st, TDS_NATIVE_TAG);
-
   ant_value_t transformer = js_mkobj(js);
-  ant_value_t transform_fn = js_heavy_mkfun(js, tds_transform, wrapper);
-  ant_value_t flush_fn = js_heavy_mkfun(js, tds_flush, wrapper);
+  ant_value_t transform_fn = js_heavy_mkfun_native(js, tds_transform, st, TDS_NATIVE_TAG);
+  ant_value_t flush_fn = js_heavy_mkfun_native(js, tds_flush, st, TDS_NATIVE_TAG);
+  
   js_set(js, transformer, "transform", transform_fn);
   js_set(js, transformer, "flush", flush_fn);
 
@@ -415,9 +420,7 @@ static ant_value_t js_tds_ctor(ant_t *js, ant_value_t *args, int nargs) {
   js->this_val = saved_this;
 
   if (is_err(ts_obj)) { free(st); return ts_obj; }
-
   js_set_slot(obj, SLOT_ENTRIES, ts_obj);
-  js_set_slot(wrapper, SLOT_ENTRIES, ts_obj);
 
   return obj;
 }
diff --git a/src/streams/compression.c b/src/streams/compression.c
index 4e94e0f..b00f074 100644
--- a/src/streams/compression.c
+++ b/src/streams/compression.c
@@ -58,11 +58,6 @@ static ant_value_t get_ts(ant_value_t obj) {
   return js_get_slot(obj, SLOT_ENTRIES);
 }
 
-static zformat_t get_wrapper_format(ant_value_t wrapper) {
-  ant_value_t fmt = js_get_slot(wrapper, SLOT_CTOR);
-  return (zformat_t)(int)js_getnum(fmt);
-}
-
 bool cs_is_stream(ant_value_t obj) {
   return is_object_type(obj)
     && (js_check_native_tag(obj, CS_Z_NATIVE_TAG) || js_check_native_tag(obj, CS_BROTLI_NATIVE_TAG))
@@ -132,9 +127,9 @@ static ant_value_t enqueue_buffer(ant_t *js, ant_value_t ctrl_obj, const uint8_t
 #define ZCHUNK_SIZE 16384
 
 static ant_value_t cs_transform(ant_t *js, ant_value_t *args, int nargs) {
-  ant_value_t wrapper = js_get_slot(js->current_func, SLOT_DATA);
+  uint32_t tag = js_get_native_tag(js->current_func);
+  zstate_t *st = (zstate_t *)js_get_native_ptr(js->current_func);
   
-  zstate_t *st = (zstate_t *)js_get_native_ptr(wrapper);
   ant_value_t ctrl_obj = (nargs > 1) ? args[1] : js_mkundef();
   ant_value_t chunk = (nargs > 0) ? args[0] : js_mkundef();
   
@@ -146,10 +141,13 @@ static ant_value_t cs_transform(ant_t *js, ant_value_t *args, int nargs) {
 
   if (!input || input_len == 0) return js_mkundef();
 
-  if (get_wrapper_format(wrapper) == ZFMT_BROTLI) {
-    brotli_stream_state_t *brotli_st = (brotli_stream_state_t *)js_get_native_ptr(wrapper);
+  if (tag == CS_BROTLI_NATIVE_TAG) {
+    brotli_stream_state_t *brotli_st = (brotli_stream_state_t *)js_get_native_ptr(js->current_func);
     return brotli_stream_transform(js, brotli_st, ctrl_obj, input, input_len);
   }
+  
+  if (tag != CS_Z_NATIVE_TAG || !st) 
+    return js_mkerr_typed(js, JS_ERR_TYPE, "Invalid CompressionStream");
 
   st->strm.next_in = (Bytef *)input;
   st->strm.avail_in = (uInt)input_len;
@@ -172,14 +170,16 @@ static ant_value_t cs_transform(ant_t *js, ant_value_t *args, int nargs) {
 }
 
 static ant_value_t cs_flush(ant_t *js, ant_value_t *args, int nargs) {
-  ant_value_t wrapper = js_get_slot(js->current_func, SLOT_DATA);
+  uint32_t tag = js_get_native_tag(js->current_func);
   ant_value_t ctrl_obj = (nargs > 0) ? args[0] : js_mkundef();
 
-  if (get_wrapper_format(wrapper) == ZFMT_BROTLI) {
-    brotli_stream_state_t *brotli_st = (brotli_stream_state_t *)js_get_native_ptr(wrapper);
+  if (tag == CS_BROTLI_NATIVE_TAG) {
+    brotli_stream_state_t *brotli_st = (brotli_stream_state_t *)js_get_native_ptr(js->current_func);
     return brotli_stream_flush(js, brotli_st, ctrl_obj);
   }
-  zstate_t *st = (zstate_t *)js_get_native_ptr(wrapper);
+  
+  zstate_t *st = (zstate_t *)js_get_native_ptr(js->current_func);
+  if (tag != CS_Z_NATIVE_TAG || !st) return js_mkerr_typed(js, JS_ERR_TYPE, "Invalid CompressionStream");
 
   st->strm.next_in = NULL;
   st->strm.avail_in = 0;
@@ -240,16 +240,22 @@ static ant_value_t js_cs_ctor(ant_t *js, ant_value_t *args, int nargs) {
   ant_value_t obj = js_mkobj(js);
   ant_value_t proto = js_instance_proto_from_new_target(js, g_cs_proto);
   if (is_object_type(proto)) js_set_proto_init(obj, proto);
+  
   js_set_native(obj, fmt == ZFMT_BROTLI ? (void *)brotli : (void *)st, fmt == ZFMT_BROTLI ? CS_BROTLI_NATIVE_TAG : CS_Z_NATIVE_TAG);
   js_set_finalizer(obj, fmt == ZFMT_BROTLI ? brotli_state_finalize : zstate_finalize);
 
-  ant_value_t wrapper = js_mkobj(js);
-  js_set_native(wrapper, fmt == ZFMT_BROTLI ? (void *)brotli : (void *)st, fmt == ZFMT_BROTLI ? CS_BROTLI_NATIVE_TAG : CS_Z_NATIVE_TAG);
-  js_set_slot(wrapper, SLOT_CTOR, js_mknum((double)fmt));
-
   ant_value_t transformer = js_mkobj(js);
-  ant_value_t transform_fn = js_heavy_mkfun(js, cs_transform, wrapper);
-  ant_value_t flush_fn = js_heavy_mkfun(js, cs_flush, wrapper);
+  
+  ant_value_t transform_fn = js_heavy_mkfun_native(js, cs_transform, fmt == ZFMT_BROTLI 
+    ? (void *)brotli : (void *)st, fmt == ZFMT_BROTLI
+    ? CS_BROTLI_NATIVE_TAG : CS_Z_NATIVE_TAG
+  );
+  
+  ant_value_t flush_fn = js_heavy_mkfun_native(js, cs_flush, fmt == ZFMT_BROTLI 
+    ? (void *)brotli : (void *)st, fmt == ZFMT_BROTLI 
+    ? CS_BROTLI_NATIVE_TAG : CS_Z_NATIVE_TAG
+  );
+  
   js_set(js, transformer, "transform", transform_fn);
   js_set(js, transformer, "flush", flush_fn);
 
@@ -268,14 +274,13 @@ static ant_value_t js_cs_ctor(ant_t *js, ant_value_t *args, int nargs) {
     return ts_obj;
   }
   js_set_slot(obj, SLOT_ENTRIES, ts_obj);
-  js_set_slot(wrapper, SLOT_ENTRIES, ts_obj);
 
   return obj;
 }
 
 static ant_value_t ds_transform(ant_t *js, ant_value_t *args, int nargs) {
-  ant_value_t wrapper = js_get_slot(js->current_func, SLOT_DATA);
-  zstate_t *st = (zstate_t *)js_get_native_ptr(wrapper);
+  uint32_t tag = js_get_native_tag(js->current_func);
+  zstate_t *st = (zstate_t *)js_get_native_ptr(js->current_func);
   ant_value_t ctrl_obj = (nargs > 1) ? args[1] : js_mkundef();
 
   ant_value_t chunk = (nargs > 0) ? args[0] : js_mkundef();
@@ -286,10 +291,13 @@ static ant_value_t ds_transform(ant_t *js, ant_value_t *args, int nargs) {
     return js_mkerr_typed(js, JS_ERR_TYPE, "The provided value is not of type '(ArrayBuffer or ArrayBufferView)'");
 
   if (!input || input_len == 0) return js_mkundef();
-  if (get_wrapper_format(wrapper) == ZFMT_BROTLI) {
-    brotli_stream_state_t *brotli_st = (brotli_stream_state_t *)js_get_native_ptr(wrapper);
+  if (tag == DS_BROTLI_NATIVE_TAG) {
+    brotli_stream_state_t *brotli_st = (brotli_stream_state_t *)js_get_native_ptr(js->current_func);
     return brotli_stream_transform(js, brotli_st, ctrl_obj, input, input_len);
   }
+  
+  if (tag != DS_Z_NATIVE_TAG || !st)
+    return js_mkerr_typed(js, JS_ERR_TYPE, "Invalid DecompressionStream");
 
   st->strm.next_in = (Bytef *)input;
   st->strm.avail_in = (uInt)input_len;
@@ -313,10 +321,10 @@ static ant_value_t ds_transform(ant_t *js, ant_value_t *args, int nargs) {
 }
 
 static ant_value_t ds_flush(ant_t *js, ant_value_t *args, int nargs) {
-  ant_value_t wrapper = js_get_slot(js->current_func, SLOT_DATA);
+  uint32_t tag = js_get_native_tag(js->current_func);
   ant_value_t ctrl_obj = (nargs > 0) ? args[0] : js_mkundef();
-  if (get_wrapper_format(wrapper) == ZFMT_BROTLI) {
-    brotli_stream_state_t *st = (brotli_stream_state_t *)js_get_native_ptr(wrapper);
+  if (tag == DS_BROTLI_NATIVE_TAG) {
+    brotli_stream_state_t *st = (brotli_stream_state_t *)js_get_native_ptr(js->current_func);
     return brotli_stream_flush(js, st, ctrl_obj);
   }
   return js_mkundef();
@@ -361,16 +369,21 @@ static ant_value_t js_ds_ctor(ant_t *js, ant_value_t *args, int nargs) {
   ant_value_t obj = js_mkobj(js);
   ant_value_t proto = js_instance_proto_from_new_target(js, g_ds_proto);
   if (is_object_type(proto)) js_set_proto_init(obj, proto);
+  
   js_set_native(obj, fmt == ZFMT_BROTLI ? (void *)brotli : (void *)st, fmt == ZFMT_BROTLI ? DS_BROTLI_NATIVE_TAG : DS_Z_NATIVE_TAG);
   js_set_finalizer(obj, fmt == ZFMT_BROTLI ? brotli_state_finalize : zstate_inflate_finalize);
 
-  ant_value_t wrapper = js_mkobj(js);
-  js_set_native(wrapper, fmt == ZFMT_BROTLI ? (void *)brotli : (void *)st, fmt == ZFMT_BROTLI ? DS_BROTLI_NATIVE_TAG : DS_Z_NATIVE_TAG);
-  js_set_slot(wrapper, SLOT_CTOR, js_mknum((double)fmt));
-
   ant_value_t transformer = js_mkobj(js);
-  ant_value_t transform_fn = js_heavy_mkfun(js, ds_transform, wrapper);
-  ant_value_t flush_fn = js_heavy_mkfun(js, ds_flush, wrapper);
+  
+  ant_value_t transform_fn = js_heavy_mkfun_native(js, ds_transform, fmt == ZFMT_BROTLI 
+    ? (void *)brotli : (void *)st, fmt == ZFMT_BROTLI 
+    ? DS_BROTLI_NATIVE_TAG : DS_Z_NATIVE_TAG
+  );
+  
+  ant_value_t flush_fn = js_heavy_mkfun_native(js, ds_flush, fmt == ZFMT_BROTLI 
+    ? (void *)brotli : (void *)st, fmt == ZFMT_BROTLI 
+    ? DS_BROTLI_NATIVE_TAG : DS_Z_NATIVE_TAG
+  );
   
   js_set(js, transformer, "transform", transform_fn);
   js_set(js, transformer, "flush", flush_fn);
@@ -391,8 +404,6 @@ static ant_value_t js_ds_ctor(ant_t *js, ant_value_t *args, int nargs) {
   }
 
   js_set_slot(obj, SLOT_ENTRIES, ts_obj);
-  js_set_slot(wrapper, SLOT_ENTRIES, ts_obj);
-
   return obj;
 }