Karolina is available for hire
Hire KarolinaKarolina Modes
Verified Expert in Engineering
JavaScript Developer
Warsaw, Poland
Toptal member since April 17, 2019
Bio
Karolina is a web application developer with over four years of experience. As a full-stack developer, Karolina can build both the front end and back end of an application. Recently, Karolina has been focused on development projects with JavaScript, React, and Node.js. However, what remains constant is her work ethic: the quality of the code she develops is paramount.
Portfolio
Under100 LLC dba Tenant Marketplace Exchange Neighbor
JavaScript, React, Node.js, Supabase, Mobile-first Design, Bolt.ai, MacOS...
Digital Arc Systems Corp
React, Node.js, Next.js, MongoDB, JavaScript, Amazon S3 (AWS S3), AWS Lambda...
Gartner - Buysmart
React, Front-end, NestJS, Material UI, Storybook...
Experience
- TypeScript - 8 years
- Amazon Web Services (AWS) - 8 years
- React - 8 years
- Node.js - 8 years
- Express.js - 6 years
- Microservices - 5 years
- GraphQL - 5 years
- SCSS - 4 years
Preferred Environment
Git, Visual Studio Code (VS Code), MacOS, Claude, GitHub Copilot
The most amazing...
...thing I've coded is an application form that was used by thousands of users every single day and I can learn something new every day.
Work Experience
[PT/Hr] Startup/FullStack expert to support marketplace MVP
2025 - 2026
Under100 LLC dba Tenant Marketplace Exchange Neighbor
- Implement new designs based on the client provided templates using React and Taliwind.css.
- Implement new features and maintain Subabase, Edge Functions, triggers and automate workflows for users of the app for sending text messages with Sinch and emails.
- Refactor and prepare code originally created by AI vibe coding for production release by fixing security issues, bad code practices and so on.
Technologies: JavaScript, React, Node.js, Supabase, Mobile-first Design, Bolt.ai, MacOS, Minimum Viable Product (MVP), Back-end Development, React Hooks, Single-page Applications (SPAs), Mobile Development, CI/CD Pipelines, SMS, Responsive Web Design (RWD), GitHub Actions, GitHub Copilot, Row-level Security (RLS), Supabase Auth, Role-based Access Control (RBAC), Mobile App Development
Full-stack MERN Developer
2025 - 2025
Digital Arc Systems Corp
- Developed a Node.js server for an online game that keeps all the players' statistics, equipment, and achievements.
- Created a bug report tool for the game that also gathers logs from the client and server and sends those to the Discord server for game developers to debug.
- Created a marketing website for a game, which also includes a portal for the development team to update news and track game analytics.
- Set up a CI/CD pipeline with GitHub and AWS to automate deployments for the web portal (both Node.js and React apps) and lambdas.
Technologies: React, Node.js, Next.js, MongoDB, JavaScript, Amazon S3 (AWS S3), AWS Lambda, AWS Elastic Beanstalk, Code Review, Unit Testing, HTTP REST, Third-party Integration, Data Visualization, Back-end, API Integration, Artificial Intelligence (AI), GraphQL, Design, GraphQL API, Firebase, ECMAScript (ES6), SaaS, Authentication, C#, Non-relational Databases, Database Design, File handling, ChatGPT, Claude, Chatbots, AI Integration, API Development, Back-end Performance, AI-generated Code, Supabase, Claude Code, Payment APIs, AI Tools, MUI CSS, Amazon Web Services (AWS), PostgreSQL, Jest, Relational Database Services (RDS), Amazon CloudWatch, Game Development, MacOS, Web Architecture, HTML, MongoDB Atlas, QA Testing, TypeORM, Amazon RDS, Back-end Development, React Hooks, React Query, Single-page Applications (SPAs), MERN Stack, Mobile Development, CI/CD Pipelines, Mobile-first Design, Mobile First, Responsive Web Design (RWD), Amazon Simple Email Service (SES), GitHub Actions, GitHub Copilot, Role-based Access Control (RBAC)
React Developer
2024 - 2024
Gartner - Buysmart
- Implemented new responsive pages in React based on Figma designs, which allow users to get knowledge about the market.
- Created new common React components used by other apps and developers across the company.
- Improved code quality by using linting tools and adding new tests that run on every build.
Technologies: React, Front-end, NestJS, Material UI, Storybook, Single-page Applications (SPAs), Next.js, Microfrontends, SCSS, Figma, REST, Agile, CI/CD Pipelines, Sass, Storyblok, UX Design, RESTFul APIs, User Experience (UX), User Interface (UI), Code Review, Unit Testing, HTTP REST, React Testing Library, Data Visualization, API Integration, React Query, Site Speed Optimization, ECMAScript (ES6), SaaS, Authentication, Google Cloud Platform (GCP), auth/rbac, Styled-components, MacOS, Web Architecture, HTML, QA Testing, React Hooks, Marketplaces, Mobile-first Design, Mobile First, Responsive Web Design (RWD), GitHub Actions, GitHub Copilot
Full-stack Developer
2023 - 2024
Colleva
- Developed an app that allows users to speak to an AI avatar and, based on the scenario, produces feedback about their communication skills.
- Prepared an analytics page with user record statistics in the app using AG Grid and AG Charts libraries.
- Tested new features prepared by other developers in the team.
Technologies: Node.js, Back-end, JavaScript, TypeScript, HTML, CSS, Full-stack, NestJS, Front-end, Test-driven Development (TDD), React, Tailwind UI, Tailwind CSS, Docker, UI Design, MERN Stack, REST, CI/CD Pipelines, OpenAI, UX Design, RESTFul APIs, User Experience (UX), User Interface (UI), Code Review, HTTP REST, Third-party Integration, Ant Design, React Testing Library, Data Visualization, API Integration, Artificial Intelligence (AI), Design, React Query, Vite, Site Speed Optimization, ECMAScript (ES6), SaaS, Authentication, Terraform, Database Design, auth/rbac, AI Integration, API Development, Back-end Performance, AI Tools, MUI CSS, Amazon Web Services (AWS), PostgreSQL, Relational Database Services (RDS), Amazon CloudWatch, Redis, Amazon Cognito, MacOS, Web Architecture, QA Testing, TypeORM, Back-end Development, React Hooks, Single-page Applications (SPAs), Mobile First, Responsive Web Design (RWD), GitHub Actions, Row-level Security (RLS), Role-based Access Control (RBAC)
Front-end React Developer
2022 - 2023
Pixelcut Inc.
- Implemented new features and bug fixes with the specification provided in Linear.
- Worked with Konva.js. Improved image editor that allows users to edit photos and create their graphics with images and texts.
- Integrated API using React Query and gRPC-web error handling.
Technologies: HTML, CSS, React, TypeScript, Front-end, JavaScript, Konva, Tailwind UI, Tailwind CSS, Figma, Storybook, Docker, Headless CMS, UI Design, REST, CI/CD Pipelines, Sass, Vite, Storyblok, Content Management Systems (CMS), Single Sign-on (SSO), UX Design, RESTFul APIs, Strapi, User Experience (UX), User Interface (UI), Code Review, HTTP REST, Third-party Integration, Babel, Ant Design, Back-end, API Integration, Artificial Intelligence (AI), Stripe, React Query, Vercel, Site Speed Optimization, ECMAScript (ES6), SaaS, Authentication, auth/rbac, File handling, Payment APIs, Cursor AI, MacOS, Web Architecture, QA Testing, React Hooks, Single-page Applications (SPAs), Mobile Development, Mobile-first Design, Mobile First, Responsive Web Design (RWD), GitHub Actions
Full-stack React Developer
2021 - 2022
Modern Animal Inc
- Implemented new features for a veterinarian platform that makes managing animal documentation easier using React and TypeScript.
- Conducted small improvements and maintenance for a React Native application—iOS and Android versions—for the veterinary platform clients.
- Improved and maintained a PDF documents generator based on the React PDF library that allows veterinarians to print full animal health documentation.
Technologies: React, Node.js, HTML, JavaScript, CSS, React Native, Jest, Front-end Development, Webpack, Figma, Emotion Library, React Router, React Navigation, Sentry, Mobile, Android, iOS, Back-end Development, React Hooks, React Query, Storybook, UI Design, MERN Stack, Mobile Development, REST, Agile, CI/CD Pipelines, Sass, MobX, Storyblok, UX Design, RESTFul APIs, User Experience (UX), User Interface (UI), Code Review, Unit Testing, Third-party Integration, Babel, React Testing Library, Data Visualization, Back-end, App Store, API Integration, GraphQL, Design, GraphQL API, ECMAScript (ES6), Authentication, PDF Generation, Database Design, File handling, API Development, Payment APIs, MUI CSS, Styled-components, Amazon Web Services (AWS), Healthcare, Amazon CloudWatch, Mobile Apps, MacOS, Web Architecture, QA Testing, TypeORM, Single-page Applications (SPAs), Twilio, SMS, Mobile-first Design, Mobile First, Responsive Web Design (RWD), GitHub Actions, Role-based Access Control (RBAC), Mobile App Development
React Developer
2020 - 2022
Secure Staffing
- Moved the old Angular code to the modern React application.
- Fixed bugs and implemented new features according to specifications in Asana.
- Deployed features very quickly, and they brought new values to the customers.
- Used many automated tools to improve code quality in React and PHP.
- Charged with implementing features from end to end, as a full-stack developer.
Technologies: React, Laravel, Web Architecture, MySQL, TypeScript, PHP 7, CSS3, NPM, Visual Studio Code (VS Code), PHP, REST APIs, Front-end, Next.js, GitHub, CSS, WebSockets, Git, Elasticsearch, Web, JavaScript, Redux, HTML, Angular, APIs, HTML5, Full-stack Development, Full-stack, SQL, Front-end Development, Webpack, Relational Databases, Databases, React Router, Back-end Development, React Hooks, Axios, Azure, UI Design, Dating Apps, REST, Agile, Sass, RESTFul APIs, User Experience (UX), User Interface (UI), Code Review, HTTP REST, Data Visualization, Back-end, API Integration, Design, Site Speed Optimization, ECMAScript (ES6), Authentication, Google Cloud Platform (GCP), File handling, MacOS, QA Testing, Single-page Applications (SPAs), SOAP, Mobile-first Design, Mobile First, Responsive Web Design (RWD), Video Streaming
Full-stack React and Node.js Developer
2021 - 2021
RoarEstimates LLC
- Implemented authorization logic and user account management into a React application.
- Managed user account data in an Express application and MongoDB.
- Provided expertise on Stripe payment integration options.
Technologies: Next.js, Node.js, React, MongoDB Atlas, JavaScript, CSS, HTML5, Stripe Payments, Minimum Viable Product (MVP), Front-end Development, Webpack, Figma, REST APIs, Google Maps, React Router, Back-end Development, React Hooks, Axios, REST, Sass, RESTFul APIs, User Experience (UX), User Interface (UI), Code Review, HTTP REST, Babel, Back-end, API Integration, GraphQL API, ECMAScript (ES6), Authentication, Prisma, MacOS, Web Architecture, HTML, QA Testing, Single-page Applications (SPAs), Marketplaces, Mobile First, Responsive Web Design (RWD)
React and Testing Developer
2020 - 2021
Billflow
- Developed new features for the dashboard and embeddable React application for no-code Stripe billing integration.
- Fixed and solved issues for the product clients using Intercom.
- Developed integration tests based on Cypress for React application.
Technologies: React, Node.js, Cypress, Front-end, TypeScript, Microservices, CSS3, NPM, PostgreSQL, Visual Studio Code (VS Code), REST APIs, Next.js, GitHub, CSS, Stripe Payments, Git, Agile Software Development, Web, JavaScript, Redux, HTML, APIs, HTML5, Jest, QA Testing, Front-end Development, Webpack, Figma, Databases, React Router, Sentry, Back-end Development, React Hooks, Axios, REST, Sass, Single Sign-on (SSO), RESTFul APIs, User Experience (UX), User Interface (UI), Code Review, Unit Testing, HTTP REST, Third-party Integration, React Testing Library, Back-end, API Integration, Stripe, Site Speed Optimization, ECMAScript (ES6), SaaS, Authentication, Non-relational Databases, Database Design, API Development, Stripe API, Relational Database Services (RDS), MacOS, Web Architecture, Single-page Applications (SPAs), Mobile-first Design, Mobile First, Responsive Web Design (RWD), Role-based Access Control (RBAC)
Senior Full-stack Developer
2018 - 2021
Madiff
- Created a platform that integrates many products developed by other teams in the company.
- Developed back-end microservices in Node.js and TypeScript. Integrated them with AWS products (SQS, SMS, ES, and so on).
- Made a complicated reports API based on partitioned tables in a PostgreSQL database.
- Built multiple React/Redux applications and libraries.
- Constructed a library that enables connections to back-end services and React applications via WebSockets.
- Wrote unit tests and improved code quality using automated tools (such as ESLint, TSLint, TypeScript, and Flow).
- Refactored and updated old React and Node.js applications to new library versions.
Technologies: Microservices, Amazon Web Services (AWS), TypeScript, Node.js, Redux, React, JavaScript, Front-end, Express.js, CSS3, NPM, GraphQL, PostgreSQL, Amazon S3 (AWS S3), AWS Lambda, Visual Studio Code (VS Code), Amazon Cognito User Pools, Amazon Simple Queue Service (SQS), AWS Amplify, REST APIs, Next.js, GitHub, CSS, NestJS, Object-oriented Programming (OOP), Git, Amazon DynamoDB, Agile Software Development, Web, MongoDB, HTML, NoSQL, APIs, HTML5, Full-stack Development, Full-stack, SQL, Material UI, Jest, Front-end Development, Webpack, Relational Databases, Databases, Cloud, TypeORM, Amazon RDS, React Router, Sentry, Back-end Development, Axios, Docker, REST, Agile, CI/CD Pipelines, Sass, RESTFul APIs, User Experience (UX), User Interface (UI), Code Review, Unit Testing, HTTP REST, Third-party Integration, React Testing Library, Back-end, API Integration, GraphQL API, ECMAScript (ES6), SaaS, Authentication, Non-relational Databases, Database Design, auth/rbac, File handling, API Development, Payment APIs, Relational Database Services (RDS), Amazon CloudWatch, Redis, Amazon Cognito, MacOS, Web Architecture, QA Testing, Figma, Test-driven Development (TDD), Single-page Applications (SPAs), Microfrontends, Mobile Development, SOAP, Mobile-first Design, Mobile First, Responsive Web Design (RWD), Amazon Simple Email Service (SES), Role-based Access Control (RBAC)
React Engineer
2020 - 2020
Motive Biosciences Inc. dba MotiveBio
- Worked on MVP project designed for tracking woman's health app.
- Implemented views and pages in React based on the provided designs in Figma.
- Prepared landing page based on Gatsby following the provided design in Figma.
Technologies: React, CSS, Redux, Tailwind CSS, Material UI, AWS Amplify, AWS Lambda, Gatsby, Minimum Viable Product (MVP), Front-end Development, Webpack, Figma, Databases, Amazon Web Services (AWS), Cloud, React Router, Sentry, Back-end Development, REST, Sass, RESTFul APIs, User Experience (UX), User Interface (UI), Code Review, HTTP REST, Back-end, API Integration, ECMAScript (ES6), Authentication, Healthcare, Relational Database Services (RDS), MacOS, HTML, QA Testing, Single-page Applications (SPAs), Mobile-first Design, Mobile First, Responsive Web Design (RWD)
Full-stack Developer
2020 - 2020
GMG GmbH
- Created an MVP project for a new color management platform.
- Rewrote the existing code to create a new application from scratch.
- Provided a starting point for the developers' team to start working on improving and implementing new features in a React-based application.
Technologies: JavaScript, HTML, CSS, PHP, Node.js, React, Minimum Viable Product (MVP), Front-end Development, Webpack, REST APIs, Back-end Development, REST, RESTFul APIs, User Experience (UX), User Interface (UI), Code Review, HTTP REST, Third-party Integration, Back-end, API Integration, Authentication, Database Design, MacOS, Web Architecture, QA Testing, Mobile First, Responsive Web Design (RWD)
Software Engineer
2017 - 2018
StepStone Services
- Created a React/Redux application used by thousands of users every day.
- Developed microservices in PHP that were connected to a Microsoft SQL database and RabbitMQ.
- Built integration tests in a framework based on Selenium.
- Created ready-to-use, React-based components that were meant to be used by other teams in the company.
- Constructed Git repositories and build plans in a Bamboo-based setup and management.
Technologies: Microservices, Adobe ColdFusion, PHP, TypeScript, Node.js, React, JavaScript, Front-end, Express.js, Swagger, PHP 7, CSS3, jQuery, NPM, GraphQL, PostgreSQL, Amazon S3 (AWS S3), AWS Lambda, Visual Studio Code (VS Code), REST APIs, GitHub, CSS, Object-oriented Programming (OOP), WebSockets, Git, Web, Redux, Amazon Web Services (AWS), HTML, APIs, HTML5, Full-stack Development, Full-stack, SQL, Jest, Front-end Development, Webpack, Rollup.js, Relational Databases, Databases, Cloud, Sentry, Back-end Development, Axios, REST, Agile, CI/CD Pipelines, Sass, Single Sign-on (SSO), RESTFul APIs, User Experience (UX), User Interface (UI), Code Review, Unit Testing, HTTP REST, Third-party Integration, Back-end, API Integration, Authentication, Non-relational Databases, Database Design, auth/rbac, File handling, API Development, Selenium, Relational Database Services (RDS), Redis, MacOS, Web Architecture, QA Testing, SOAP, Bootstrap, Java, TestCafe, Mobile First, Responsive Web Design (RWD), Amazon Simple Email Service (SES)
Full-stack Developer
2015 - 2017
4 Medicine
- Contributed to the development of an MVC PHP application that includes complicated algorithms and reports.
- Prepared MySQL database architecture and migrations.
- Created simple React components that replaced legacy jQuery code.
Technologies: JavaScript, PHP, Front-end, Express.js, PHP 7, CSS3, jQuery, NPM, GraphQL, PostgreSQL, Visual Studio Code (VS Code), REST APIs, GitHub, CSS, Git, Web, Redux, HTML, APIs, HTML5, Full-stack Development, Full-stack, SQL, Material UI, Front-end Development, Relational Databases, Databases, Back-end Development, REST, RESTFul APIs, User Experience (UX), User Interface (UI), Code Review, HTTP REST, Back-end, Authentication, Database Design, auth/rbac, File handling, API Development, Healthcare, Relational Database Services (RDS), Web Architecture, QA Testing, Bootstrap, Role-based Access Control (RBAC)
Experience
Scholly Editor
A web application that allows users to enter or upload essays and correct grammar and style. My job was to refactor the front-end part based on the old code and apply a new design. The application was developed with React.
Ogury for Publishers
https://publishers.ogury.co/An application for publishers and developers to integrate a consent-management platform (CMP) to their app. As a full-stack developer and team member, I created a lot of principal components and microservices in this big application, both on the front end (React, Redux) and back end (Node.js, TypeScript). I also supported other teams and helped with other microservices, as they did not have enough people or knowledge to implement a specific feature.
Miniature Painting Gallery
A simple React/Redux one-page portfolio application with enabled translations and a contact form. This is an old project; similar ones can be done very quickly in just a few days by using ready-to-implement tools, such as Material UI.
Simple RWD Landing Page
This is a very simple old RWD landing page that was developed in pure CSS and Vanilla JavaScript, without using React this time.
Link to the code: https://github.com/kkawalec/simple-rwd-landing-page
Link to the code: https://github.com/kkawalec/simple-rwd-landing-page
Education
2011 - 2016
Master's Degree in Church Music
The Fryderyk Chopin University of Music - Warsaw, Poland
Skills
Libraries/APIs
React, Node.js, React Router, API Development, jQuery, AWS Amplify, REST APIs, Rollup.js, Google Maps, Emotion Library, React Navigation, React Query, Konva, MobX, React Testing Library, Stripe, GraphQL API, Stripe API
Tools
Amazon Cognito, Figma, GitHub Copilot, Git, Amazon Simple Queue Service (SQS), NPM, Amazon Simple Email Service (SES), GitHub, MongoDB Atlas, Webpack, Sentry, Babel, Prisma, ChatGPT, Claude, Claude Code, Amazon CloudWatch, Terraform
Languages
GraphQL, TypeScript, JavaScript, CSS, HTML, HTML5, ECMAScript (ES6), PHP 7, CSS3, SCSS, SQL, Sass, PHP, C#, Java
Frameworks
Redux, Express.js, NestJS, Swagger, Next.js, Material UI, React Native, Tailwind CSS, Laravel, Cypress, Jest, Ant Design, Bootstrap, MUI CSS, Angular, TestCafe, Selenium
Paradigms
Microservices, Web Architecture, Mobile Development, Database Design, Responsive Web Design (RWD), Role-based Access Control (RBAC), Agile Software Development, Object-oriented Programming (OOP), Test-driven Development (TDD), UI Design, Microfrontends, REST, Agile, UX Design, Unit Testing
Platforms
Amazon Web Services (AWS), Web, AWS Elastic Beanstalk, AWS Lambda, Docker, Storyblok, Firebase, Twilio, MacOS, Visual Studio Code (VS Code), Adobe ColdFusion, Mobile, Android, iOS, Azure, Vercel, Google Cloud Platform (GCP)
Storage
PostgreSQL, Relational Databases, MongoDB, NoSQL, Redis, Amazon DynamoDB, MySQL, Elasticsearch, Amazon S3 (AWS S3), Databases
Industry Expertise
Healthcare
Other
Music, Front-end, APIs, Full-stack Development, Full-stack, QA Testing, Minimum Viable Product (MVP), Front-end Development, TypeORM, Back-end Development, React Hooks, Back-end, Single-page Applications (SPAs), CI/CD Pipelines, RESTFul APIs, User Interface (UI), API Integration, SaaS, Authentication, auth/rbac, Relational Database Services (RDS), Mobile First, Mobile-first Design, GitHub Actions, WebSockets, Amazon Cognito User Pools, Stripe Payments, Gatsby, Cloud, Amazon RDS, Axios, Tailwind UI, Storybook, Headless CMS, MERN Stack, Vite, Strapi, User Experience (UX), Code Review, HTTP REST, Third-party Integration, Data Visualization, Artificial Intelligence (AI), Site Speed Optimization, Non-relational Databases, PDF Generation, File handling, SOAP, Chatbots, AI Integration, Back-end Performance, AI-generated Code, Supabase, Payment APIs, Cursor AI, AI Tools, Styled-components, Mobile Apps, Game Development, Marketplaces, SMS, Row-level Security (RLS), Supabase Auth, Mobile App Development, Video Streaming, Dating Apps, Content Management Systems (CMS), Single Sign-on (SSO), OpenAI, App Store, Design, Bolt.ai
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