Andrej Gajdos, UI Development Developer in Prague, Czech Republic
Andrej Gajdos

UI Development Developer in Prague, Czech Republic

Member since August 31, 2016
Andrej is a technology consultant and software engineer with a focus on the front-end in React. He has over eight years of experience delivering software and has worked for clients worldwide in many industries. He delivered solutions for startups, digital agencies, and big companies, such as Apple or Binance. A background in computer science and his ability as a full-stack developer allows him to create everything from small business websites to custom web applications.
Andrej is now available for hire


  • Self-employed
    JavaScript, React, Node.js, MongoDB, PostgreSQL, MySQL
  • Nash
    D3.js, TypeScript, Styled-components, GraphQL, Gatsby, React, JavaScript
  • FastSwims
    Redux-Saga, React, JavaScript



Prague, Czech Republic



Preferred Environment

OS X, VS Code

The most amazing...

...thing I've developed is a pixel-perfect user interface for Apple.


  • Senior Full-stack Developer

    2017 - PRESENT
    • Refactored and improved code bases that saved customers at least six figures in the future development.
    • Mentored senior React developers with best practices, design patterns, and tooling to scale React applications in terms of maintainability and performance.
    • Developed interactive data visualization that renders thousands of buildings on a map, and users can edit buildings by editing polygons.
    Technologies: JavaScript, React, Node.js, MongoDB, PostgreSQL, MySQL
  • React and Gatsby Developer

    2018 - 2019
    • Built customizable UI components used across multiple projects. Built a functional prototype of funds management and payments system in the exchange platform.
    • Worked on the Nash Extension, a browser-based cryptocurrency wallet, and Chrome extension.
    • Built the company website in React, Gatsby, and TypeScript.
    Technologies: D3.js, TypeScript, Styled-components, GraphQL, Gatsby, React, JavaScript
  • React Developer

    2018 - 2018
    • Designed and built a functional prototype of an event management platform for organizing swimming teams and swimming competitions.
    • Designed a new user interface based on the customer’s prototypes.
    • Built a functional prototype from scratch as a single-page application.
    Technologies: Redux-Saga, React, JavaScript
  • React Developer

    2018 - 2018
    • Helped deliver a React Native project used for managing fitness studios.
    • Fixed various bugs and issues in the project.
    • Optimized the project for the Android platform.
    Technologies: Redux, React Native
  • Principal Software Engineer

    2017 - 2018
    • Worked as a full-stack JavaScript developer using React and Node.js.
    • Designed and built an interactive podcast platform. Podcasters can upload audio files and add "spots" to specific moments in their podcasts, which can be anything from links to social media posts, videos, or images. Listeners are engaged with content, such as social media posts or preview of external web pages.
    • Built a single-page app from scratch with a complex user interface, including user interactions and animations.
    • Designed and developed a RESTful API server.
    Technologies: InVision, Twitter API, Babel, Webpack, SVG, D3.js, Redux, React, Knex.js, Objection.js, Koa, Node.js, JavaScript, PostgreSQL, Amazon S3 (AWS S3), Heroku
  • Pre-sales Engineer

    2016 - 2017
    • Presented and demonstrated products to potential customers from all over the world.
    • Demonstrated product features to developer teams and showed how to use them in the development process with a specific workflow, environment, and toolset.
    • Helped sales associates close deals by presenting our products in specific use-cases.
    • Trained sales associates in how to effectively present and sell our tools to developer teams and managers.
    • Assisted customers with installation, troubleshooting, and other customer service for configuration issues.
    Technologies: Java
  • Software Engineer

    2015 - 2016
    • Worked mostly as a front-end developer on dashboards and data visualizations.
    • Implemented new features and fixed bugs in enterprise applications used for data quality management, rewrote UI components to modern technologies.
    • Designed and implemented the front end of an interactive application for customer data management.
    • Designed and implemented the server-to-sever communication and a server push in the GWT application.
    Technologies: Errai, ActiveMQ, JMS, JSTL, JSP, D3.js, Babel, Gulp, Webpack, SCSS, Bootstrap, jQuery, Backbone.js, Immutable.js, Flux, React, Emacs, JavaScript, Java
  • Data Visualization Developer

    2013 - 2015
    Techniserv, Taranzo
    • Analyzed, designed, and implemented solutions for gathering and processing structured and unstructured data from social networks and various other sources.
    • Designed and implemented a module for building and visualizing a social network.
    Technologies: JUNG, Twitter API, YouTube API, OrientDB, D3.js, Bootstrap, jQuery, JSTL, JSP, Maven, Spring MVC, Liferay, JavaScript, Java
  • Software Tester

    2012 - 2013
    Amberg Group
    • Executed both manual and automated tests and analyzed the results.
    • Developed and maintained the whole test infrastructure with automated tests.
    • Designed test cases, wrote documentation, and reported issues.
    Technologies: Ruby, Python, JavaScript


  • Stackbit

    Stackbit is a website builder that helps developers of any level build their Jamstack sites based on Next.js and Tailwind fast. I helped Stackbit’s team set up the tooling and design the architecture for the design system of the main platform. I helped and mentored senior React developers on best practices and patterns to use to solve complex flows in React projects. I was working on fixing various issues and bugs in the platform. I was working on additional feature sets for enterprise clients.

  • Getctrl

    Getctrl is a customer data platform for customer success professionals. Ctrl empowers post-sales people to bring data together from different apps to create their workspaces. I worked as a front-end developer to develop new features and fix the existing codebase. I also helped and mentored senior React developers' best practices.

  • Nash

    A blazing fast static website built with React and Gatsby. All pages are fully responsive and optimized for mobile viewing.

    Development tools: JavaScript, React, Gatsby, Styled-components, TypeScript

  • Cryptocurrency Exchange Platform

    A Cryptocurrency exchange platform. I joined as a React developer. I was working on implementing a design system, portfolio management, and payment systems. I used React, Typescript, Storybook, and GraphQL.

  • Security Tokens Offering Platform

    A secure, customer-centric, decentralized online securities exchange marketplace that allows investors at all levels to buy and sell digital securities. The customer is a leading cryptocurrency exchange. I worked as a Senior Front-End Engineer. I operated as an architect for front-end implementation and made reviews, and audits of the code of other front-end developers.

  • System Master PLanner

    A computational tool for master planners, energy and resource managers, and policymakers. It allows users to evaluate sustainability and resiliency scenarios for large buildings and other assets. I worked as a React developer and developed interactive data visualization, rendering thousands of buildings as polygons on a Leaflet map.

  • FastSwims

    An event management platform for managing swimming teams and swimming competitions. I designed a new user interface based on customer’s prototypes and built a functional prototype.

    Development tools: JavaScript, React, Redux-Saga

  • Saycaster Rebranded to Bitcast

    An interactive podcast platform:

    - Podcasters upload their audio and add 5-20 spots to their podcasts
    - These spots can be anything from links, to social media posts, to other videos or images
    - Listeners can listen and comment on these specific spots

    Development tools: JavaScript, Node.js, Koa.js, PostgreSQL, Heroku, React, Redux, D3.js

  • Sushi Migrator

    A web3 project where users can migrate LP positions from Uniswap to SushiSwap. Users can interact with the Ethereum blockchain through Metamask. Users can see the ERC-20 tokens list and list of their LP positions. Users can add new ERC-20 tokens.

  • Vertigo

    A project for a company in the marine industry. I worked as a data visualization specialist to build an interactive visualization of a Neo4j graph database. I developed this visualization in React, D3.js, and Storybook.

  • Potentials

    I build the user interface for this eCommerce tool in React. It helps the CEO and sales associates to maintain and process details about potential customers. I built the user interface using React and Tailwind.

  • Filipi

    Filipi is a furniture eCommerce store built with Next.js, Node.js, and MySQL. I helped the owner migrate the whole solution to another server and fix various issues and bugs in SEO, managing data, and setting up analytics tools.

  • Tauchain

    I created a node.js back-end service that processes data from third-party APIs like third-party exchanges, Github API, Twitter API, and Telegram API. The server is deployed on AWS. I helped the client fix the whole project after previous developers, and I replaced the headless CMS solution.

  • Software Development Blog

    My freelance software development blog. Built with WordPress and JavaScript.

  • Ivana Neckarova

    Personal WordPress website, where I customized the template to achieve unique design and responsiveness for mobile devices. I set up WordPress plugins to improve the websites, performance, and search engine optimization.

  • Link Preview Generator

    Get preview data (a title, description, image, domain name) from a URL. The library uses Puppeteer headless browser to scrape the website.

    Development tools: Node.js, Puppeteer

  • Neo Transfer

    Neo-transfer allows you to log in with a private key, see balance, and transfer NEO or GAS within TestNet. The project is based on JS SDK for NEO blockchain.

    Development tools: Neon.js, React, Redux, Redux-Saga, Twitter Bootstrap

  • Newsfeed Cryptogoods

    A newsfeed for events on cryptogoods with a single, responsive page.

    Development tools: JavaScript, React, Redux, Redux-Saga, Twitter Bootstrap

  • Authenticating Users in SPA using Node, Passport, React and Redux

    User authentication in a single-page application with Node, React, Redux and Koa combined with Passport.

    Development tools: JavaScript, Node.js, React, Redux, Passport.js

  • Nested Datatables

    jQuery DataTables plugin for rendering nested data tables in rows. Inner tables are independent of the data and layout from the outer table.

    Development tools: JavaScript, jQuery

  • Webpack Setup for ES6, React, Sass, and Bootstrap

    Webpack configuration to bundle ES6, React, Sass, and Bootstrap for production and development.

    Development tools: JavaScript, React, Webpack

  • Social Graph

    A Liferay portlet to visualize a social network as a directed multigraph. Jung library is used for building the multigraph, which is stored in OrientDB. Visualization and other components are built in D3.js and Bootstrap.

    Development tools: Java, JavaScript, Liferay, JSP, Jung, OrientDB, D3.js, Bootstrap

  • SVG Sprite into PNG

    A workflow converts SVG sprite into PNG images utilizing Gulp.

    Development tools: JavaScript, Gulp

  • Server Push in GWT Application with Errai

    Implementation of server push messages from server to client in GWT application with Errai framework.

    Development tools: Java, GWT, Errai

  • Contract Generator Tool

    Some insurance brokers have a list of insurances and clients in XLS format and need to generate various contracts based on a contract template in DOC and DOCx format. The user can set up a database (XLS or XLSx) and required columns, which will be parsed into the contract. The application has a database of insurance in SQLite. The main window contains a list of clients with detailed information, where the user can instantly search clients, add required information (date, overpayment, insurance from database), choose contract templates, and generate a contract (DOC or DOCx) for the client. The UI is built in WPF and ADO.NET is used for parsing data from a Microsoft Excel file.

    Development tools: C#/.NET, WPF, SQLite, ADO.NET

  • Personal Calendar

    A basic personal calendar application with two view modes (week/month). The application generates log files and uses a MySQL database. The presentation layer is built in Swing and SwingWorker. Connections to the database are developed in JDBC. The project contains simple JSP pages for viewing a list of events and their detailed information.

    Development tools: Java, JSP, Swing, SwingWorker, MySQL, JDBC

  • Guide to Data Synchronization in Microsoft SQL Server (Publication)
    Sharing related information among isolated systems has become increasingly important. There are many methods to choose from to perform that task for SQL Server, but it’s important to know which is better for each use case.
  • A Guide to Managing Webpack Dependencies (Publication)
    The Webpack module bundler processes JavaScript code and all static assets, such as stylesheets, images, and fonts. However, configuring Webpack and its dependencies can be cumbersome and not always a straightforward process, especially for beginners. In this article, Toptal Software Engineer Andrej Gajdos provides a guide with examples on how to configure Webpack for different scenarios and points out the most common pitfalls connected to project dependencies and their bundling when using Webpack.


  • Languages

    JavaScript 6, JavaScript, Object-oriented JavaScript (OOJS), CSS, HTML, CSS3, Java, HTML5, Less, SCSS, Sass, ECMAScript (ES6), SQL, TypeScript, C, Python, Ruby, PHP, C#, UML, C++, GraphQL
  • Frameworks

    Next.js, Express.js, Koa, Redux, Bootstrap, Spring MVC, Flux, JUnit, JSP, Errai, React Native, Ruby on Rails (RoR), JavaServer Pages (JSP), Swing, Windows Presentation Foundation (WPF), .NET, Tailwind CSS
  • Libraries/APIs

    Underscore.js, React, Passport.js, jQuery Plugins, jQuery UI, Redux-Saga, D3.js, Node.js, Immutable.js, JSTL, Chai, jQuery, AWS Amplify, GitHub API, Twitter API, YouTube API, Objection.js, JDBC, Backbone.js, OpenGL, Win32 API, WinForms, JMS, LeafletJS, MobX, Web3.js
  • Paradigms

    Model View Controller (MVC), Object-relational Mapping (ORM), Agile Software Development, Functional Programming, REST, Object-oriented Programming (OOP), Object-oriented Design (OOD), Software Testing, Automated Testing, Responsive Layout, Agile
  • Storage

    JSON, PostgreSQL, Amazon S3 (AWS S3), Graph Databases, SQLite, MySQL, OrientDB, MongoDB
  • Other

    Responsive UI, UI Development, Ajax, Front-end, Single-page Applications (SPA), Web Development, Front-end Development, Front-end Architecture, APIs, Back-end, ESLint, Technical Consulting, Back-end Development, Writing & Editing, Data Visualization, Presentations, Sales, Customer Service, Consulting, Programming, Software Design, Styled-components, Gatsby, Full-stack, Prismic, Webhook, Storybook, API Integration, AWS, JUNG, SVG, Web Scraping, Social Networks Development, Data Analysis, Liferay, BPM, Messaging Patterns, Sales Presentations, Chrome Extensions, Ethers.js
  • Tools

    Redux Thunk, Webpack, Gulp, Bower, Mocha, Emacs, PostCSS, Knex.js, Babel, GitLab, GitHub Pages, GitHub, Trello, InVision, ActiveMQ, Maven, VS Code
  • Platforms

    Firebase, Java EE, WordPress, Amazon Lightsail, AWS Lambda, Amazon Web Services (AWS), OS X, Heroku, Amazon, MacOS, Windows, Linux, Blockchain


  • Master's Degree in Service Science, Management, and Engineering
    2013 - 2015
    Masaryk University Brno - Brno
  • Erasmus Exchange Student in Master in Innovation and Research in Informatics
    2014 - 2014
    Polytechnic University of Catalonia - Barcelona
  • Bachelor's Degree in Applied Informatics
    2009 - 2013
    Masaryk University - Brno

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