Senior MERN Developer (React.js + Node.js)

<p> <strong>Headquarters:</strong> Sweden <br /><strong>URL:</strong> <a href="http://career.proxify.io">http://career.proxify.io</a> </p> <h3><strong>The Role:</strong></h3> <p>We are looking for a Senior MERN Stack Developer with heavy specialization in React.js and Node.js on behalf of one of our high-growth clients to architect, scale, and maintain high-throughput web applications. In this role, you will take operational ownership of both front-end user interfaces and back-end microservices, delivering seamless, secure, and responsive digital products. You will bridge user-facing features with complex database architectures and cloud infrastructure. You are a perfect candidate if you are growth-oriented, you love what you do, and you enjoy working on new ideas to develop exciting products</p> <p><strong> </strong></p> <h4><strong>What we are looking for:</strong></h4> <ul> <li>5+ years of professional software engineering experience designing, building, and deploying end-to-end applications using MongoDB, Express.js, React.js, and Node.js.</li> <li>Deep proficiency in modern JavaScript (ES6+), TypeScript, asynchronous programming, event loops, and memory management across client and server environments.</li> <li>Deep mastery of React internals, custom hooks, component design patterns, state management (Redux Toolkit, Zustand, or React Query), SSR/SSG frameworks (Next.js is a strong plus), and performance optimization (virtualization, code splitting, Web Vitals).</li> <li>Proven experience architecting scalable RESTful APIs, WebSockets, and/or GraphQL services. Proficiency with middleware design, authentication protocols (JWT, OAuth2, Passport.js), and event-driven architectures.</li> <li>Advanced knowledge of MongoDB schema design, aggregation pipelines, index strategy, performance tuning, and ORMs/ODMs like Mongoose or Prisma.</li> <li>Strong commitment to test-driven development using frameworks like Jest, React Testing Library, and Cypress, alongside hands-on