Bartłomiej Łoza
Verified Expert in Engineering
Full-stack Developer
Warsaw, Poland
Toptal member since July 27, 2020
Bart is a seasoned full-stack JavaScript developer with over a decade of hands-on experience using a variety of frameworks (Redux, Angular, AngularJS, and React Native), and libraries (React, Node.js, and Vue.js). Bart has a wide range of experience working as a senior developer and team leader for major corporations like Lufthansa, ERGO, and IGT (formerly Gtech), PZU, PLAY, and Danske Bank and also for US-based startups, SOCI and LabFellows.
Portfolio
Experience
- Node.js - 10 years
- React - 7 years
- Python 3 - 7 years
- TypeScript - 7 years
- React Native - 6 years
- Next.js - 5 years
- AI Engineering - 4 years
- Amazon Bedrock AgentCore - 2 years
Preferred Environment
Jira, Slack, GitHub, Chrome, Visual Studio Code (VS Code), MacOS
The most amazing...
...project I've implemented was a Mapbox-based app for a real estate broker where I led a 4-person team in order to develop an E2E project in three months.
Work Experience
Software Engineer
The Blackstone Group
- Developed a high-performance web application using React and Next.js, increasing user engagement through an intuitive interface and streamlined authentication flows.
- Engineered secure API integrations with Python and FastAPI, reducing data processing times and enhancing overall system responsiveness.
- Orchestrated the creation of a scalable development environment on AWS with Terraform, cutting deployment time and boosting infrastructure reliability.
- Optimized front-end performance by refactoring code and enforcing best practices in React and Next.js, achieving a 15% reduction in page load times.
- Integrated OpenAI APIs to power intelligent document parsing and real-time chat interfaces, enhancing internal knowledge access for enterprise users.
- Implemented a custom chunking and embedding pipeline with Python and LangChain, storing vectors in Pinecone and metadata in DynamoDB for fast semantic search.
- Designed and deployed a secure AI chat system using Next.js and FastAPI, enabling contextual document-based conversations with strict access control.
- Collaborated on retrieval-augmented generation (RAG) pipelines to combine internal data with LLMs, improving answer relevance and user trust in AI responses.
Full-stack Software Engineer
Endeavor
- Played a pivotal role in defining and executing tasks, drawing on business requirements to guide development. This involved integrating 3rd-party software for enhanced marketing and notification capabilities.
- Implemented several key features that enhanced user experience, such as advanced permission settings and interactive poll functionalities.
- Managed the application release process efficiently, ensuring smooth and timely deployments.
- Extended my expertise beyond traditional coding. Actively engaged in both front-end and back-end development, ensuring seamless integration and functionality.
- Contributed to the DevOps aspects of the project, gaining valuable experience in this area.
Team Lead
Danske Bank
- Prepared a concept of a shared component library based on React, Storybook, and styled-components.
- Prepared and implemented an optimal architecture for a system that has been operating for several years.
- Implemented, in barely two months and under a very tight deadline, a critical module for a huge Danske Bank mobile application.
Lead Front-end Engineer
SOCI, Inc.
- Migrated a project from ES5 to the ES6+ JavaScript version.
- Implemented a fully responsive mobile version of the application.
- Introduced ES6+ features during internal workshops for other employees.
Team Lead
LabFellows
- Designed a new architecture concept, mainly related to performance optimization, state management, and API facade.
- Introduced newest React concepts to the front-end team like React Hooks, Portal API, mainly based on my knowledge gained during ReactiveConf in Prague.
- Prepared a refactoring roadmap (instructions on how to deal with the old code, chunk by chunk).
- Supported, educated, and prepared dedicated workshops for younger members of the front-end team.
- Rearchitected contracts between the front end (FE) and back end (BE) made together with the back-end team leader.
- Prepared ESLint, prettier configurations, and introduced pre-commit hooks.
Full-stack Developer
Lufthansa Innovation Hub
- Implemented an itinerary React Native MVP app from scratch.
- Designed data models and contracts between the front end and back end.
- Implemented new screens and flows which were based in the US and wireframes prepared carefully in advance by our BAs and designers.
Full-stack Developer
Ergo Digital IT
- Refactored a React application in order to use best practices.
- Implemented Node.js microservice for PDF generation purposes.
- Introduced a Redux state management architecture concept.
Full-stack Developer
IGT (formerly Gtech)
- Developed a back-office AngularJS-based application with a strong focus on charts.
- Refactored an Angular-based application to Redux architecture.
- Adjusted and deployed a stable version of the lottery CRM app in North Carolina (US).
Senior Front-end Developer
PZU
- Developed a directed self-service application for individual customers.
- Implemented web designs in order to support even IE6.
- Introduced Angular concepts during internal workshops.
Full-stack Developer
PLAY
- Designed and implemented Flux-like, component-based architecture on top of AngularJS with the addition of Highcharts.
- Designed and developed a series of highly configurable offer form controls.
- Implemented a communication system between the CRM and embedded applications.
Full-stack Developer
AUTOMATUM
- Designed and implemented a single-page application (SPA) with multiple dynamic forms.
- Implemented mechanisms that made clients' data anonymous for certain system users (privileges system).
- Implemented algorithms prepared by a financial analyst.
System Architect | Full-stack Developer
TTG Events
- Designed and implemented the architecture of the internal CRM system.
- Implemented algorithms used for matching potential clients with tourism agencies.
- Implemented a React-based internal application and WordPress widget used for the registration of potential customers.
Junior PHP/JavaScript Developer
Kompan.pl
- Wrote the documentation and took care of the maintenance of an internal CRM application based on the Symfony-like PHP framework.
- Implemented a procurement module for a culinary school.
- Implemented modules (private messages, friends network, and user preferences) for a social network application.
Junior Front-end Developer
Freelance Work
- Implemented landing pages based on designs prepared in Photoshop.
- Adjusted WordPress themes according to client requirements.
- Prepared the HTML and CSS layers of the pages based on the designs.
Experience
PZU Self Service App
I was a front-end developer. My role was to create a pixel-perfect implementation of the design and flows based on user stories prepared by BAs and designers. The application was Angular based along with some Backbone.js and XSLT transformations.
eCommerce Admin Panel
I was the team leader of a distributed front-end team responsible for implementing the admin panel from scratch. It was a challenging project because my team consisted of six front-end developers, and my role was to architect the app and implement new features as well as coordinating the whole team so that we made progress in the correct direction. I also prepared the backlog and user stories based on the designs delivered in advance.
eProcurement Platform for Science
I was the team leader of the front-end team who joined the project at a very critical moment. On one hand, my role was to refactor the React codebase because it had very big technical debt and on the other, I was also guiding two front-end developers in the implementation. The application was implemented in React without any state management system or even tests.
My Implementation Tasks:
• Redux State Management
• E2E Tests in Cypress
• Jest Unit Tests
• Proper ESLint and a Prettier Configuration
• React Hooks
Education
Master of Engineering Degree in Computer Science
Warsaw University of Technology - Warsaw, Poland
Certifications
Psychology of Emotions Part 2
Starway Institute
Auditing Security and Protecting Web Applications
IT Security: Audits & Trainings (Niebezpiecznik.pl)
NLP 2
Starway Institute
Psychology of HR
STARWAY Institute
Psychology of Sales
STARWAY Institute
NLP 1
Starway Institute
Agile Leadership — Management 3.0
Management 3.0 (Management30.com)
Psychology of Marketing
Starway Institute
Psychology of Emotions Part 1
Starway Institute
Psychology of Management
Starway Institute
Angular 2 Space
Tomasz Borowski
Skills
Libraries/APIs
React, Node.js, REST APIs, OpenAI API, Zod, Zod Schema, Stripe, LinkedIn API, Vue, jQuery, Highcharts, Flexbox, Chai, Backbone.js, Redux-Saga, Playwright
Tools
Jira, Git, Google Kubernetes Engine (GKE), Claude, Shadcn, Claude Code, GitHub, Slack, Gulp, Grunt, Webpack, Karma, Xcode, Android Studio, Webpack 4, AWS Command Line Interface (CLI), Terraform, Celery
Languages
JavaScript, GraphQL, TypeScript, CSS, HTML, Python, Python 3, PHP, HTML5, CSS3, ECMAScript (ES6), Java, XSLT, Sass, SQL
Frameworks
Redux, Material UI, Next.js, Angular, AngularJS, React Native, Tailwind CSS, Electron, Chrome, Symfony, Jasmine, Protractor, Jest, Express.js, Cypress, NestJS, LlamaIndex
Paradigms
Agile, REST, Search Engine Optimization (SEO), Testing, Responsive Web Design (RWD), BEM, Model Context Protocol (MCP)
Platforms
WordPress, Vercel, iOS, Google Cloud Platform (GCP), Kubernetes, Mapbox, MacOS, Visual Studio Code (VS Code), Docker, Amazon Web Services (AWS), Android, AWS Lambda
Storage
PostgreSQL, MongoDB, Redis, Relational Databases, MySQL
Other
Architecture, FastAPI, RESTFul APIs, Front-end Architecture, Code Review, Headless CMS, Full-stack Development, Full-stack, Single-page Applications (SPAs), APIs, CI/CD Pipelines, Mobile Apps, LangChain, Zustand, Artificial Intelligence (AI), Large Language Models (LLMs), Agentic AI, Retrieval-augmented Generation (RAG), Vector Databases, AI Tools, WebSockets, Agentic RAG Systems, Workflow Automation, Large Language Model Operations (LLMOps), Supabase, AI-generated Code, Cursor AI, Generative Artificial Intelligence (GenAI), Multi-tenant SaaS, SaaS, Workflow Automation & System Integration, Webhooks, AI Engineering, Enzyme, Styled-components, GitHub Actions, Progressive Web Applications (PWAs), Strapi, OpenAI, Artificial General Intelligence (AGI), AI Chatbots, AI Agents, Vite, Amazon Bedrock AgentCore
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