How to Build a POS App with Node.js

In this blog, we will learn how to build a POS App with Node.js using Medusa JS and Flutter.

Introduction

A Point of Sale (POS) application is an essential tool for retail stores, restaurants, supermarkets, and businesses that need to manage sales, inventory, customers, and payments efficiently.

Modern POS systems help businesses streamline checkout operations, track inventory in real time, generate sales reports, and manage customer information from a centralized platform.

What is a POS App?

A Point of Sale (POS) application is software that enables businesses to process customer purchases, manage inventory, track sales, and generate reports.

A POS system typically includes:

Product Management
Inventory Tracking
Customer Management
Order Processing
Payment Management
Sales Reporting
Barcode Scanning
Receipt Generation

Medusa offers modular commerce APIs, workflows, and extensibility that simplify POS development.

Learn more about Medusa in its official documentation.

How Does It Work?

The POS application communicates with the Medusa backend through custom POS APIs.

The backend handles:

Catalog and Inventory Management
Checkout and Order Processing
Barcode-Based Product Lookup
Sales Reporting

The Flutter mobile application sends API requests to the backend and receives JSON responses that can be rendered in the POS interface.

Why Use Medusa for POS Development?

High Performance & Modular Architecture

Medusa provides a flexible backend structure that allows developers to easily build and customize POS features such as product management, barcode scanning, checkout, and inventory tracking.

Real-Time Inventory Updates

Inventory levels are automatically updated after every completed transaction, ensuring accurate stock visibility.

Cross-Platform Support

A single Medusa backend can power Android, iOS, web, and desktop POS applications simultaneously.

Features of the POS App

The POS application can include the following features:

Secure Staff Authentication (Cashier Login)
Register Session Management (Open/Close Cash Drawer)
Product Catalog & Search
Barcode Scanning
Inventory Tracking
Shopping Cart Management
Hold and Resume Carts (Held Carts)
Customer Management (Attach/Create Customers)
Checkout & Multiple Payment Methods
PDF Invoice Generation & Printing

What We Are Building

We will build a simple cashier-focused POS workflow consisting of:

Medusa JS Backend

Custom APIs for:

Product Catalog Retrieval
Barcode-Based Product Lookup

Flutter Mobile App

A responsive mobile application that:

Displays available products
Supports product searching
Scans product barcodes
Retrieves product information from Medusa APIs

Prerequisites

Node.js 20 or later
PostgreSQL
Flutter SDK
Medusa JS CLI
Android Studio or Xcode
VS Code

Backend Development

In this section, we will create the APIs required to retrieve product data and perform barcode-based product lookups.

Step 1: Initialize the Medusa JS Backend

Create a new Medusa application:

npx create-medusa-app@latest pos-backend

1	npx create-medusa-app@latest pos-backend

Navigate to the project:

cd pos-backend

1	cd pos-backend

Medusa automatically sets up the required commerce modules and database configuration.

Step 2: Create a Catalog API

import {
  MedusaRequest,
  MedusaResponse,
} from "@medusajs/framework/http";

export async function GET(
  req: MedusaRequest,
  res: MedusaResponse
) {
  const catalog = [
    {
      id: "prod_1",
      title: "Medusa T-Shirt",
      sku: "MEDUSA-TSHIRT-M",
      price: 15.00,
      barcode: "123456789012",
    },
  ];

  res.json({ catalog });
}

import {

MedusaRequest,

MedusaResponse,

} from "@medusajs/framework/http";

export async function GET(

req: MedusaRequest,

res: MedusaResponse

) {

const catalog = [

{

id: "prod_1",

title: "Medusa T-Shirt",

sku: "MEDUSA-TSHIRT-M",

price: 15.00,

barcode: "123456789012",

];

res.json({ catalog });

}

This endpoint returns product information that can be displayed in the POS application, including product name, SKU, price, and barcode details.

Step 3: Create a Barcode Lookup API

import {
  MedusaRequest,
  MedusaResponse,
} from "@medusajs/framework/http";

export async function GET(
  req: MedusaRequest,
  res: MedusaResponse
) {
  const { barcode } = req.query;

  if (!barcode) {
    return res.status(400).json({ 
      message: "Barcode query parameter is required" 
    });
  }

  // Lookup the specific variant matching the scanned barcode.
  // In a production application, query the Medusa Product Module.
  const variant = {
    id: "variant_1",
    title: "M / White",
    product_id: "prod_1",
    sku: "MEDUSA-TSHIRT-M",
    price: 15.00,
    barcode: barcode
  };

  res.json({ variant });
}

import {

MedusaRequest,

MedusaResponse,

} from "@medusajs/framework/http";

export async function GET(

req: MedusaRequest,

res: MedusaResponse

) {

const { barcode } = req.query;

if (!barcode) {

return res.status(400).json({

message: "Barcode query parameter is required"

});

}

// Lookup the specific variant matching the scanned barcode.

// In a production application, query the Medusa Product Module.

const variant = {

id: "variant_1",

title: "M / White",

product_id: "prod_1",

sku: "MEDUSA-TSHIRT-M",

price: 15.00,

barcode: barcode

};

res.json({ variant });

}

This endpoint accepts a barcode and returns the matching product variant from the Medusa catalog.

Backend Dashboard Output

Flutter POS Application Development

In this section, we will connect the application to the Medusa backend, implement barcode scanning, and display product information for cashiers.

Step 1: Create the Flutter Application

Create a new Flutter project:

flutter create pos_mobile_app

1	flutter create pos_mobile_app

cd pos_mobile_app

1	cd pos_mobile_app

Add required packages to pubspec.yaml:

dependencies:
  flutter:
    sdk: flutter

  dio: ^5.9.0
  mobile_scanner: ^6.0.11

dependencies:

flutter:

sdk: flutter

dio: ^5.9.0

mobile_scanner: ^6.0.11

Install packages:

flutter pub get

1	flutter pub get

Step 2: Configure API Communication

import 'package:dio/dio.dart';

class CatalogRemoteDataSource {
  const CatalogRemoteDataSource(this._dio);

  final Dio _dio;

  // Retrieve the POS product catalog
  Future<List<Map<String, dynamic>>> fetchCatalog({String query = ''}) async {
    final response = await _dio.get<Map<String, dynamic>>(
      '/pos/catalog',
      queryParameters: <String, dynamic>{
        'limit': 250,
        if (query.trim().isNotEmpty) 'q': query.trim(),
      },
    );

    final catalog = response.data?['catalog'] as List<dynamic>? ?? const <dynamic>[];
    return catalog.map((item) => Map<String, dynamic>.from(item as Map)).toList();
  }

  // Lookup scanned barcode in Medusa JS
  Future<Map<String, dynamic>?> lookupBarcode(String barcode) async {
    final response = await _dio.get<Map<String, dynamic>>(
      '/pos/catalog/barcode',
      queryParameters: <String, dynamic>{'barcode': barcode},
    );

    final variant = response.data?['variant'];
    return variant != null ? Map<String, dynamic>.from(variant as Map) : null;
  }
}

import 'package:dio/dio.dart';

class CatalogRemoteDataSource {

const CatalogRemoteDataSource(this._dio);

final Dio _dio;

// Retrieve the POS product catalog

Future<List<Map<String, dynamic>>> fetchCatalog({String query = ''}) async {

final response = await _dio.get<Map<String, dynamic>>(

'/pos/catalog',

queryParameters: <String, dynamic>{

'limit': 250,

if (query.trim().isNotEmpty) 'q': query.trim(),

);

final catalog = response.data?['catalog'] as List<dynamic>? ?? const <dynamic>[];

return catalog.map((item) => Map<String, dynamic>.from(item as Map)).toList();

}

// Lookup scanned barcode in Medusa JS

Future<Map<String, dynamic>?> lookupBarcode(String barcode) async {

final response = await _dio.get<Map<String, dynamic>>(

'/pos/catalog/barcode',

queryParameters: <String, dynamic>{'barcode': barcode},

);

final variant = response.data?['variant'];

return variant != null ? Map<String, dynamic>.from(variant as Map) : null;

}

Step 3: Implement Barcode Scanning

Create a barcode scanner screen using the mobile_scanner

import 'package:flutter/material.dart';
import 'package:mobile_scanner/mobile_scanner.dart';

class BarcodeScannerScreen extends StatefulWidget {
  const BarcodeScannerScreen({super.key});

  @override
  State<BarcodeScannerScreen> createState() => _BarcodeScannerScreenState();
}

class _BarcodeScannerScreenState extends State<BarcodeScannerScreen> {
  bool _handled = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Scan Barcode'),
      ),
      body: MobileScanner(
        onDetect: (capture) {
          if (_handled) return;

          // Prevent StateError by safely checking if barcodes list is empty
          final code = capture.barcodes.isEmpty 
              ? null 
              : capture.barcodes.first.rawValue;
              
          if (code != null && code.isNotEmpty) {
            _handled = true;
            // Pop the scanned value back to the previous screen
            Navigator.pop(context, code);
          }
        },
      ),
    );
  }
}

import 'package:flutter/material.dart';

import 'package:mobile_scanner/mobile_scanner.dart';

class BarcodeScannerScreen extends StatefulWidget {

const BarcodeScannerScreen({super.key});

@override

State<BarcodeScannerScreen> createState() => _BarcodeScannerScreenState();

}

class _BarcodeScannerScreenState extends State<BarcodeScannerScreen> {

bool _handled = false;

@override

Widget build(BuildContext context) {

return Scaffold(

appBar: AppBar(

title: const Text('Scan Barcode'),

body: MobileScanner(

onDetect: (capture) {

if (_handled) return;

// Prevent StateError by safely checking if barcodes list is empty

final code = capture.barcodes.isEmpty

? null

: capture.barcodes.first.rawValue;

if (code != null && code.isNotEmpty) {

_handled = true;

// Pop the scanned value back to the previous screen

Navigator.pop(context, code);

}

);

}

Step 4: Connect Scanner to Product Catalog UI

In the cashier catalog view, add a scan action button that opens the scanner and adds the resolved product to the cart.

// Launch scanner screen and wait for the code
final scannedBarcode = await Navigator.push<String>(
  context,
  MaterialPageRoute(builder: (_) => const BarcodeScannerScreen()),
);

if (scannedBarcode != null) {
  // Call the Medusa API to resolve the barcode
  final productVariant = await catalogDataSource.lookupBarcode(scannedBarcode);
  
  if (productVariant != null) {
    // Add the found variant to the cashier shopping cart
    cartBloc.add(CartItemAdded(productVariant));
  } else {
    ScaffoldMessenger.of(context).showSnackBar(
      const SnackBar(content: Text('Product not found for this barcode.')),
    );
  }
}

// Launch scanner screen and wait for the code

final scannedBarcode = await Navigator.push<String>(

context,

MaterialPageRoute(builder: (_) => const BarcodeScannerScreen()),

);

if (scannedBarcode != null) {

// Call the Medusa API to resolve the barcode

final productVariant = await catalogDataSource.lookupBarcode(scannedBarcode);

if (productVariant != null) {

// Add the found variant to the cashier shopping cart

cartBloc.add(CartItemAdded(productVariant));

} else {

ScaffoldMessenger.of(context).showSnackBar(

const SnackBar(content: Text('Product not found for this barcode.')),

);

}

POS Mobile Application Output

Medusa POS Application

Access the complete product catalog, search items, and filter by categories.
Manage active carts, attach customer details, apply discounts, and process payments.

Scan product barcodes with the camera for instant lookup and fast checkout.

Conclusion

Medusa JS provides a flexible foundation for building a POS App with Node.js, offering features such as product management, barcode scanning, and inventory tracking.

This approach simplifies POS development and supports applications across multiple platforms.

You can also explore other informative blogs on Mobikul for more knowledge.

ankit.mobikul322

26 Jun, 2026
Created by - ankit.mobikul322

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