diff --git a/packages/core/js-client/src/api.ts b/packages/core/js-client/src/api.ts
index d153bb4e..031066c1 100644
--- a/packages/core/js-client/src/api.ts
+++ b/packages/core/js-client/src/api.ts
@@ -28,7 +28,7 @@ import {
   aqua2js,
   SchemaValidationError,
   js2aqua,
-  wrapFunction,
+  wrapJsFunction,
 } from "./compilerSupport/conversions.js";
 import { ServiceImpl } from "./compilerSupport/types.js";
 import { FluencePeer } from "./jsPeer/FluencePeer.js";
@@ -103,7 +103,7 @@ export const v5_callFunction = async (
           );
         }
 
-        return [argName, wrapFunction(arg, argSchema)];
+        return [argName, wrapJsFunction(arg, argSchema)];
       }
 
       if (typeof arg === "function") {
@@ -204,7 +204,7 @@ export const v5_registerService = (
   // Wrapping service impl to convert their args ts -> aqua and backwards
   const wrappedServiceImpl = Object.fromEntries(
     Object.entries(serviceImpl).map(([name, func]) => {
-      return [name, wrapFunction(func, serviceSchema[name])];
+      return [name, wrapJsFunction(func, serviceSchema[name])];
     }),
   );
 
diff --git a/packages/core/js-client/src/compilerSupport/conversions.ts b/packages/core/js-client/src/compilerSupport/conversions.ts
index 6bbd1ff2..a740ef6b 100644
--- a/packages/core/js-client/src/compilerSupport/conversions.ts
+++ b/packages/core/js-client/src/compilerSupport/conversions.ts
@@ -202,7 +202,9 @@ export function js2aqua(
   }
 }
 
-export const wrapFunction = (
+// Wrapping function, converting its arguments to aqua before call and back to js after call.
+// It makes callbacks and service functions defined by user operate on js types seamlessly
+export const wrapJsFunction = (
   func: ServiceImpl[string],
   schema:
     | ArrowWithoutCallbacks
diff --git a/packages/core/js-client/src/services/builtins.ts b/packages/core/js-client/src/services/builtins.ts
index b6541fa8..b5e23c61 100644
--- a/packages/core/js-client/src/services/builtins.ts
+++ b/packages/core/js-client/src/services/builtins.ts
@@ -68,13 +68,15 @@ const parseWithSchema = <T extends z.ZodTypeAny>(
 ): [z.infer<T>, null] | [null, string] => {
   const result = schema.safeParse(req.args, {
     errorMap: (issue, ctx) => {
-      if (issue.code === z.ZodIssueCode.invalid_type) {
-        if (issue.path.length === 1 && typeof issue.path[0] === "number") {
-          const [arg] = issue.path;
-          return {
-            message: `Argument ${arg} expected to be of type ${issue.expected}, Got ${issue.received}`,
-          };
-        }
+      if (
+        issue.code === z.ZodIssueCode.invalid_type &&
+        issue.path.length === 1 &&
+        typeof issue.path[0] === "number"
+      ) {
+        const [arg] = issue.path;
+        return {
+          message: `Argument ${arg} expected to be of type ${issue.expected}, Got ${issue.received}`,
+        };
       }
 
       if (issue.code === z.ZodIssueCode.too_big) {
@@ -340,8 +342,7 @@ export const builtInServices: Record<
     }),
 
     concat_strings: withSchema(z.array(z.string()))((args) => {
-      const res = "".concat(...args);
-      return success(res);
+      return success(args.join(""));
     }),
   },
 
diff --git a/packages/core/js-client/src/services/securityGuard.ts b/packages/core/js-client/src/services/securityGuard.ts
index 1417e52b..2ebac50b 100644
--- a/packages/core/js-client/src/services/securityGuard.ts
+++ b/packages/core/js-client/src/services/securityGuard.ts
@@ -19,6 +19,8 @@ import { PeerIdB58 } from "@fluencelabs/interfaces";
 
 import { ParticleContext } from "../jsServiceHost/interfaces.js";
 
+// Helpers for validating service function
+
 /**
  * A predicate of call params for sig service's sign method which determines whether signing operation is allowed or not
  */