> Markdown version of [/jobs/ext/2392773-senior-frontend-engineer-sell-online](https://www.wearedevelopers.com/jobs/ext/2392773-senior-frontend-engineer-sell-online). Every page supports `.md` or `Accept: text/markdown`. Links point to the HTML versions so they work for humans too. Agent guide: [/agents.md](https://www.wearedevelopers.com/agents.md).

---

# Senior Frontend Engineer - Sell Online

- **Company:** SumUp
- **Location:** Köln, Germany
- **Experience:** Expert
- **Contract:** Permanent contract
- **Skills:** Clean Code Principles, JavaScript (Programming Language), Application Performance Management, Continuous Integration, Live Connect (Windows), Scrum Methodology, E2e Testing, Next.js, TypeScript, ReactJS, Front End Software Development, React Testing Library, JestJS
- **Published:** August 12, 2026
- **Apply:** https://de.indeed.com/viewjob?jk=a1122add42c166c2

## About the Role

* You have 5+ years of experience in TypeScript and JavaScript, with hands-on experience building production-grade React and Next.js applications (including SSR and app router patterns)
 * You have experience writing unit, integration, and end-to-end tests using tools like Jest, Vitest, or React Testing Library
 * You're comfortable working within CI/CD workflows and collaborating in agile environments (Scrum or Kanban)
 * You have experience with UI libraries such as Radix or shadcn, and a solid understanding of accessibility and UX best practices
 * You have a product mindset - someone who cares about the value delivered to merchants, not just the code written to get there, and who can work autonomously to drive complex features end-to-end

## Description

* Build and maintain frontend features across payment links, gift cards, and online checkout products, writing clean, testable, and maintainable code
 * Contribute to the development and upkeep of our integration products and SDKs, used by both internal teams and external partners
 * Take part in technical planning, design reviews, and sprint ceremonies - bringing your perspective on estimations, trade-offs, and improvements
 * Help reduce tech debt and improve application performance, observability, and accessibility as a foundation for future delivery
 * Monitor live services and respond to issues, providing redundancy for customer support requests reaching the team


## Related Videos

- [Watch Tests Go Brrrr! : Getting Started with Cypress in ReactJS](https://www.wearedevelopers.com/videos/282-watch-tests-go-brrrr-getting-started-with-cypress-in-reactjs)
- [GraphQL + Apollo + Next.js: A Lovely Trio](https://www.wearedevelopers.com/videos/311-graphql-apollo-next-js-a-lovely-trio)
- [Modern Headless Commerce with Vendure](https://www.wearedevelopers.com/videos/489-modern-headless-commerce-with-vendure)
- [From Zero to Hero: NextJS 13 and Tailwind CSS for Beginners](https://www.wearedevelopers.com/videos/766-from-zero-to-hero-nextjs-13-and-tailwind-css-for-beginners)
- [To New Frontiers: The Future of Frontend Development](https://www.wearedevelopers.com/videos/404-to-new-frontiers-the-future-of-frontend-development)
- [Create a Programmatic SEO Project Using Next.js and Static Site Generation](https://www.wearedevelopers.com/videos/449-create-a-programmatic-seo-project-using-next-js-and-static-site-generation)

## Related Articles

- [Frontend Developer Salary in Germany [2023]](https://www.wearedevelopers.com/magazine/195-frontend-developer-salary-in-germany-2023)
- [The Biggest German Tech Companies](https://www.wearedevelopers.com/magazine/424-the-biggest-german-tech-companies)
- [16 Best Free React UI Libraries in 2025](https://www.wearedevelopers.com/magazine/148-16-best-free-react-ui-libraries-in-2025)
- [The Best 7 Frontend Frameworks for Developers in 2025](https://www.wearedevelopers.com/magazine/400-the-best-7-frontend-frameworks-for-developers-in-2025)
- [Backend Developer Salary in Germany [2023]](https://www.wearedevelopers.com/magazine/196-backend-developer-salary-in-germany-2023)
- [React Developer Salary [2023]](https://www.wearedevelopers.com/magazine/198-react-developer-salary-2023)