Senior Frontend Developer (React.js).

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Warsaw (Poland)

Hybrid

Who we are:

Adaptiq is a technology hub specializing in building, scaling, and supporting R&D teams for high-end, fast-growing product companies in a wide range of industries.

About the Product:

An interactive online entertainment platform delivers a portfolio of browser-based games and real-time features to a rapidly expanding user base. The system addresses challenges of high traffic, low-latency updates, and secure micro-transactions within a social gaming context. It operates a hybrid technology stack that includes a mature codebase built on a widely used DOM-manipulation library alongside modern React and Next.js frameworks. Key technical hurdles include migrating legacy components to a modular architecture, implementing WebSocket-based real-time interactions, ensuring mobile and cross-browser consistency, and integrating payment flows and promotion management interfaces. Strong engineering leadership is essential to maintain stability, drive performance optimizations, and accelerate feature delivery at scale.

About the Role:

As a Senior Frontend Developer, you will own the end-to-end delivery of user-facing features on a complex platform. You will clarify requirements, propose architectural solutions, and implement robust interfaces that meet both legacy and future needs. Reporting to a front-end lead and collaborating with a front-end architect, backend engineers, designers, QA, and DevOps, you will spearhead the migration from a jQuery-based codebase to a component-driven React/Next.js ecosystem. This role demands autonomy, strong communication, and deep technical expertise to modernize build processes, optimize performance metrics, and uphold security best practices. Your contributions will shape the frontend architecture, tooling, and workflows that enable rapid, scalable growth.

Key Responsibilities:

Enhance and optimize existing jQuery interfaces for performance, stability, and maintainability
Develop responsive, scalable applications using jQuery, React, and Next.js
Refactor and modularize large CSS/SCSS architectures to support maintainability and scalable theming
Ensure high-quality mobile user experience and cross-browser compatibility
Maintain and extend WebSocket integrations for real-time updates
Implement front-end security measures, including input validation and secure coding patterns
Design and define React component architecture to guide progressive migration efforts
Integrate RESTful APIs and Next.js API routes, coordinating closely with backend services
Establish performance benchmarking, automated testing, and build pipelines with tools like Vite, Webpack, or Gulp
Architect centralized state management solutions using Redux, MobX, or similar libraries
Collaborate with designers to translate UI/UX prototypes into production-ready code
Develop business-critical features such as payment flows, authentication systems, and promotion management interfaces

Required Competence and Skills:

6+ years of frontend development on high-load, production-grade projects
Deep expertise in jQuery and maintaining legacy codebases
Strong React.js skills (Hooks, functional components, context, custom hooks)
Proficiency with Next.js (SSR, SSG, App Router, API routes)
Mastery of CSS/SCSS, responsive design, CSS Grid, and Flexbox
Fluency in modern JavaScript (ES6+) and TypeScript
Experience with asynchronous programming patterns and WebSocket integration
Proven performance optimization techniques, including bundle analysis and Core Web Vitals
Familiarity with build tools such as Webpack, Vite, and Gulp
Expertise in RESTful API integration and front-end security best practices
Experience resolving cross-browser compatibility and debugging issues
Knowledge of state management libraries (Redux, MobX, or equivalents)
Proficient with Git and collaborative development workflows
Excellent communication skills and proven ability to work autonomously in cross-functional teams