Senior Frontend Developer (вакансія неактивна)

Description
We’re looking for an experienced Frontend Developer to join our team in Warsaw office and work on a high-load web platform. You’ll maintain and optimize our legacy jQuery system while preparing the technical foundation for migration to a modern React/Next.js stack. This role offers the opportunity to tackle real production challenges in a performance-critical environment, collaborate with cross-functional teams, and directly influence the future architecture of our platform.

Requirements
— 4–6 years of frontend development experience with high-load, production-grade projects
— Advanced expertise in jQuery and legacy codebase maintenance
— Strong experience with React.js (Hooks, functional components, context, custom hooks)
— Next.js proficiency (SSR/SSG, API routes, App Router)
— Mastery of CSS/SCSS, including responsive design, Grid, Flexbox.
— Proficiency in JavaScript (ES6+), including async programming and WebSocket integration
— Experience with performance optimization techniques (bundle analysis, Core Web Vitals, mobile performance)
— Skilled with build tools such as Webpack, Vite, and Gulp
— Familiarity with RESTful API integration and security best practices
— Experience with cross-browser compatibility, debugging, and responsive design principles

Nice to Have
— TypeScript and strategies for gradual adoption
— Basic understanding of PHP for backend API integration
— Experience with testing frameworks (Jest, React Testing Library, Cypress)
— GSAP for advanced animations and interactive UI elements
— Familiarity with design tools (Figma, Zeplin, Photoshop, Sketch)
— Knowledge of CI/CD pipelines and DevOps fundamentals
— SEO and web analytics understanding
— A/B testing platforms and conversion optimization experience

Soft Skills
— Detail-oriented with precision in high-load environments
— Excellent communication and collaboration skills across cross-functional teams
— Problem-solving mindset with an analytical approach to performance and architecture challenges
— Adaptable and comfortable working with both legacy and modern technologies
— Ownership mentality, taking responsibility for code quality and system stability

Responsibilities
— Maintain and optimize the existing jQuery 2.2.4 codebase for performance and stability
— Refactor and modularize large CSS architectures for maintainability
— Ensure mobile UX quality and cross-browser compatibility
— Maintain and enhance WebSocket integrations for real-time features
— Implement security improvements and input validation processes
— Plan and design React component architecture for future migration
— Develop API integration strategies for Next.js
— Establish performance benchmarking and testing infrastructure
— Modernize build processes with Vite and other tools
— Design and implement centralized state management solutions
— Develop business-critical features such as payment flows, authentication systems, and promotion management interfaces
— Support and enhance A/B testing and conversion optimization tools