[js] Support associative access on type objects.

src/vm/js/nqp-runtime/deserialization.js

@@ -511,14 +511,11 @@ BinaryCursor.prototype.deserialize = function(sc) {
     if (objects[i].is_array) {
       sc.root_objects[i] = [];
     } else {
-      sc.root_objects[i] = new (STable_for_obj.obj_constructor)();
+      sc.root_objects[i] = objects[i].is_concrete
+        ? new (STable_for_obj.obj_constructor)()
+        : STable_for_obj.createTypeObject();
       sc.root_objects[i]._SC = sc;
     }
-
-    if (!objects[i].is_concrete) {
-      // TODO think more about it
-      sc.root_objects[i].type_object_ = 1;
-    }
   }
 
   for (var i = 0; i < STables.length; i++) {

src/vm/js/nqp-runtime/reprs.js

@@ -5,10 +5,10 @@ var NQPInt = require('./nqp-int.js');
 function basic_type_object_for(HOW) {
   var st = new sixmodel.STable(this, HOW);
   this._STable = st;
-  var obj = new st.obj_constructor();
 
+  var obj = st.createTypeObject();
   this._STable.WHAT = obj;
-  obj.type_object_ = 1;
+
   return obj;
 }
 

src/vm/js/nqp-runtime/sixmodel.js

@@ -67,6 +67,15 @@ function injectMethod(proto, name, method) {
   };
 }
 
+STable.prototype.createTypeObject = function() {
+  var obj = new this.obj_constructor();
+  obj.type_object_ = 1;
+  obj.$$atkey = function(key) {
+    return null;
+  };
+  return obj;
+};
+
 STable.prototype.setMethodCache = function(method_cache) {
   // TODO delete old methods
   var proto = this.obj_constructor.prototype;