Bartłomiej Łoza, Developer in Warsaw, Poland
Bartłomiej is available for hire
Hire Bartłomiej

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.


Danske Bank
Node.js, Redux-Saga, Jest, Cypress, TypeScript, GraphQL, Redux, Java...
SOCI, Inc.
Backbone.js, Responsive Web Design (RWD), jQuery, HTML5, CSS3, JavaScript
Styled-components, Webpack 4, Material UI, Jest, Cypress, Redux, React...




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

Team Lead

2019 - PRESENT
Danske Bank
  • Prepared and implemented an optimal architecture for a system that has been operating for several years.
  • Prepared a concept of a shared component library based on React, Storybook, and styled-components.
  • Implemented, in barely two months and under a very tight deadline, a critical module for a huge Danske Bank mobile application.
Technologies: Node.js, Redux-Saga, Jest, Cypress, TypeScript, GraphQL, Redux, Java, React Native, React, Architecture, Single-page Applications (SPA), Next.js, WordPress, Search Engine Optimization (SEO), Vercel

Lead Front-end Engineer

2019 - 2019
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.
Technologies: Backbone.js, Responsive Web Design (RWD), jQuery, HTML5, CSS3, JavaScript

Team Lead

2018 - 2019
  • 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.
Technologies: Styled-components, Webpack 4, Material UI, Jest, Cypress, Redux, React, ECMAScript (ES6)

Full-stack Developer

2018 - 2018
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.
Technologies: Enzyme, Jest, Android Studio, Xcode, Redux, React Native, ECMAScript (ES6)

Full-stack Developer

2017 - 2018
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.
Technologies: Docker, Webpack, Express.js, Jest, PostgreSQL, Node.js, Redux, React

Full-stack Developer

2016 - 2017
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).
Technologies: Protractor, Chai, Karma, Jasmine, Node.js, Docker, Flexbox, Webpack, Redux, Angular, AngularJS, ECMAScript (ES6)

Senior Front-end Developer

2016 - 2016
  • Developed a directed self-service application for individual customers.
  • Implemented web designs in order to support even IE6.
  • Introduced Angular concepts during internal workshops.
Technologies: CSS3, HTML5, BEM, Sass, XSLT, Backbone.js, Angular

Full-stack Developer

2014 - 2016
  • 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.
Technologies: Highcharts, Node.js, CSS3, HTML5, jQuery, JavaScript, Grunt, Gulp, AngularJS

Full-stack Developer

2014 - 2015
  • 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.
Technologies: CSS, HTML, JavaScript, React

System Architect | Full-stack Developer

2012 - 2015
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.
Technologies: jQuery, React, JavaScript, CSS, HTML, MySQL, PHP

Junior PHP/JavaScript Developer

2012 - 2013
  • 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.
Technologies: jQuery, CSS, HTML, JavaScript, Symfony, PHP

Junior Front-end Developer

2009 - 2012
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.
Technologies: jQuery, HTML, CSS, JavaScript

PZU Self Service App

The project involved a PZU self-service application.

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

This project involved building an eCommerce application from scratch.

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 is a 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
2009 - 2014

Master of Engineering Degree in Computer Science

Warsaw University of Technology - Warsaw, Poland


Psychology of Emotions Part 2

Starway Institute


Auditing Security and Protecting Web Applications

IT Security: Audits & Trainings (



Starway Institute


Psychology of HR

STARWAY Institute


Psychology of Sales

STARWAY Institute



Starway Institute


Agile Leadership — Management 3.0

Management 3.0 (


Psychology of Marketing

Starway Institute


Psychology of Emotions Part 1

Starway Institute


Psychology of Management

Starway Institute


Angular 2 Space

Tomasz Borowski


React, REST APIs, Node.js, Vue, jQuery, Highcharts, Flexbox, Chai, Backbone.js, Redux-Saga


Git, GitHub, Slack, Jira, Gulp, Grunt, Webpack, Karma, Xcode, Android Studio, Webpack 4


Redux, Next.js, Angular, AngularJS, React Native, Chrome, Symfony, Jasmine, Protractor, Jest, Express.js, Cypress, Material UI


JavaScript, CSS, GraphQL, TypeScript, HTML, PHP, HTML5, CSS3, ECMAScript (ES6), Java, XSLT, Sass


Search Engine Optimization (SEO), Responsive Web Design (RWD), BEM


WordPress, Vercel, Mapbox, MacOS, Visual Studio Code (VS Code), Docker


MongoDB, MySQL, PostgreSQL


Single-page Applications (SPA), Architecture, Enzyme, Styled-components

Collaboration That Works

How to Work with Toptal

Toptal matches you directly with global industry experts from our network in hours—not weeks or months.


Share your needs

Discuss your requirements and refine your scope in a call with a Toptal domain expert.

Choose your talent

Get a short list of expertly matched talent within 24 hours to review, interview, and choose from.

Start your risk-free talent trial

Work with your chosen talent on a trial basis for up to two weeks. Pay only if you decide to hire them.

Top talent is in high demand.

Start hiring