ensure the js object has a internal field

src/engines/v8/generate.zig

@@ -723,6 +723,12 @@ fn getNativeObject(
         obj_ptr.* = T{};
     } else {
         // retrieve the zig object from it's javascript counterpart
+
+        // check if the js object has a least one internal field.
+        if (js_obj.internalFieldCount() == 0) return JSError.InvalidArgument;
+
+        // TODO ensure the js object corresponds to the expected native type.
+
         const ext = js_obj.getInternalField(0).castTo(v8.External).get().?;
         if (comptime T_refl.is_mem_guarantied()) {
             // memory is fixed

src/tests/types_native_test.zig

@@ -289,11 +289,15 @@ pub fn exec(
     };
     try tests.checkCases(js_env, &separate_cases);
 
-    // Test for the bug #185: native func expects a object but the js value is
-    // not.
-    // https://github.com/lightpanda-io/jsruntime-lib/issues/185
     var bug_native_obj = [_]tests.Case{
+        // Test for the bug #185: native func expects a object but the js value is
+        // not.
+        // https://github.com/lightpanda-io/jsruntime-lib/issues/185
         .{ .src = "try { car.changeBrand('foo'); false; } catch(e) { e instanceof TypeError; }", .ex = "true" },
+        // Test for the bug #187: native func expects a native object but the js value is
+        // not.
+        // https://github.com/lightpanda-io/jsruntime-lib/issues/187
+        .{ .src = "try { car.changeBrand({'foo': 'bar'}); false; } catch(e) { e instanceof TypeError; }", .ex = "true" },
     };
     try tests.checkCases(js_env, &bug_native_obj);
 }