diff --git a/module/json.cpp b/module/json.cpp
index 3771206..04d2feb 100644
--- a/module/json.cpp
+++ b/module/json.cpp
@@ -51,6 +51,7 @@ private:
     usize line = 1;
     usize ptr = 0;
     token this_token;
+    var temp_stack = nil;
 
 private:
     std::string var_generate(var&);
@@ -72,7 +73,7 @@ private:
     }
     void next();
     void match(token_type);
-    var vector_member(gc*);
+    void vector_member(nas_vec&, gc*);
     var vector_object_generate(gc*);
     void hash_member(nas_hash&, gc*);
     var hash_object_generate(gc*);
@@ -224,34 +225,31 @@ void json::match(token_type type) {
     return;
 }
 
-var json::vector_member(gc* ngc) {
-    auto result = nil;
+void json::vector_member(nas_vec& vec, gc* ngc) {
     if (this_token.type==token_type::tok_lbrace) {
-        result = hash_object_generate(ngc);   
+        vec.elems.push_back(hash_object_generate(ngc));   
     } else if (this_token.type==token_type::tok_lbrkt) {
-        result = vector_object_generate(ngc);
+        vec.elems.push_back(vector_object_generate(ngc));
     } else if (this_token.type==token_type::tok_str) {
-        result = ngc->newstr(this_token.content);
+        vec.elems.push_back(ngc->newstr(this_token.content));
         next();
     } else if (this_token.type==token_type::tok_num) {
-        result = var::num(str2num(this_token.content.c_str()));
+        vec.elems.push_back(var::num(str2num(this_token.content.c_str())));
         next();
     }
-    return result;
 }
 
 var json::vector_object_generate(gc* ngc) {
     auto vect_object = ngc->alloc(vm_type::vm_vec);
-    auto& vec = vect_object.vec().elems;
-    ngc->temp = vect_object;
+    temp_stack.vec().elems.push_back(vect_object);
     match(token_type::tok_lbrkt);
-    vec.push_back(vector_member(ngc));
+    vector_member(vect_object.vec(), ngc);
     while(this_token.type==token_type::tok_comma) {
         match(token_type::tok_comma);
-        vec.push_back(vector_member(ngc));
+        vector_member(vect_object.vec(), ngc);
     }
     match(token_type::tok_rbrkt);
-    ngc->temp = nil;
+    temp_stack.vec().elems.pop_back();
     return vect_object;
 }
 
@@ -282,7 +280,7 @@ void json::hash_member(nas_hash& hash, gc* ngc) {
 
 var json::hash_object_generate(gc* ngc) {
     auto hash_object = ngc->alloc(vm_type::vm_hash);
-    ngc->temp = hash_object; // cause problem
+    temp_stack.vec().elems.push_back(hash_object);
     match(token_type::tok_lbrace);
     hash_member(hash_object.hash(), ngc);
     while(this_token.type==token_type::tok_comma) {
@@ -290,7 +288,7 @@ var json::hash_object_generate(gc* ngc) {
         hash_member(hash_object.hash(), ngc);
     }
     match(token_type::tok_rbrace);
-    ngc->temp = nil;
+    temp_stack.vec().elems.pop_back();
     return hash_object;
 }
 
@@ -308,9 +306,17 @@ var json::parse(const std::string& input, gc* ngc) {
     text = input;
     next();
     if (this_token.type==token_type::tok_lbrkt) {
-        return vector_object_generate(ngc);
+        ngc->temp = temp_stack = ngc->alloc(vm_type::vm_vec);
+        auto result = vector_object_generate(ngc);
+        ngc->temp = nil;
+        temp_stack = nil;
+        return result;
     } else {
-        return hash_object_generate(ngc);
+        ngc->temp = temp_stack = ngc->alloc(vm_type::vm_vec);
+        auto result = hash_object_generate(ngc);
+        ngc->temp = nil;
+        temp_stack = nil;
+        return result;
     }
     return nil;
 }
diff --git a/test/json.nas b/test/json.nas
index c8f3167..263c4be 100644
--- a/test/json.nas
+++ b/test/json.nas
@@ -1,4 +1,5 @@
 use std.json;
+use module.libjson;
 use std.process_bar;
 
 var ss = json.stringify({
@@ -18,6 +19,7 @@ var ss = json.stringify({
 
 println(ss, "\n");
 println(json.parse(ss), "\n");
+println(libjson.parse(ss), "\n");
 
 var ss = json.stringify([{
     vec:[0,1,2,3],
@@ -35,8 +37,9 @@ var ss = json.stringify([{
 
 println(ss, "\n");
 println(json.parse(ss), "\n");
+println(libjson.parse(ss), "\n");
 
-func {
+var test_json = func(json) {
     var bar = process_bar.high_resolution_bar(30);
     var tmp = [
         {t0:nil},
@@ -50,18 +53,25 @@ func {
     ];
 
     srand();
-    foreach(var h; tmp) {
-        var name = keys(h)[0];
-        h[name] = [];
+    foreach(var hash; tmp) {
+        var name = keys(hash)[0];
+        hash[name] = [];
         print("\e[1000D", bar.bar(0));
         for(var i = 0; i<500; i+=1) {
-            append(h[name], {id:i, content:int(rand()*1e7)});
+            append(hash[name], {id:i, content:int(rand()*1e7)});
             print("\e[1000D", bar.bar((i+1)/500));
         }
         print("\e[1000D", bar.bar(1), " executing...\n");
     }
     print("\e[1000D", "\e["~str(size(tmp))~"A");
-    foreach(var h; json.parse(json.stringify(tmp))) {
-        println("\e[1000D", bar.bar(1), " parse done ", keys(h)[0], " ", size(h[keys(h)[0]]));
+    foreach(var hash; json.parse(json.stringify(tmp))) {
+        println("\e[1000D", bar.bar(1), " parse done ", keys(hash)[0], " ", size(hash[keys(hash)[0]]));
     }
-}();
\ No newline at end of file
+};
+
+var stamp = maketimestamp();
+test_json(libjson);
+println("time usage: ", stamp.elapsedUSec()/1000, " ms");
+stamp.stamp();
+test_json(json);
+println("time usage: ", stamp.elapsedUSec()/1000, " ms");