Juan Elfers
Senior Frontend Engineer | JavaScript & React Specialist
I’m a senior software engineer with 10+ years of experience delivering reliable, scalable web applications. I turn complex requirements into clean, maintainable solutions that drive real impact quickly.
Beyond coding, I’m passionate about improving team workflows, mentoring developers (including several years guiding students and professionals on Codementor), and ensuring projects move smoothly from idea to production.
I’ve helped startups and established companies accelerate development cycles, improve product quality, and scale platforms serving thousands of users daily. Along with deep technical expertise, I bring the ability to collaborate, guide, and deliver measurable results.
Core skills: React.js, Next.js, Node.js, TypeScript/JavaScript, databases (SQL/MongoDB), Tailwind, HTML/CSS, UX/UI, deployments on Vercel & AWS.
REVIEWS FROM CLIENTS
Full Stack Engineer & Mentor @ Codementor | Top Featured Mentor
For over 5+ years I’ve mentored and support...
Full Stack Engineer & Mentor @ Codementor | Top Featured Mentor
For over 5+ years I’ve mentored and supported 500+ developers and students worldwide through Codementor, guiding code reviews, debugging, and project delivery. Recognized as a Top Featured Mentor, I’ve built long-term relationships with clients and consistently maintained high ratings for the quality of my work.
Alongside mentoring, I’ve delivered hundreds of production-ready features across diverse stacks—primarily with React, Next.js, Node.js, and modern databases—helping startups and established teams accelerate development, enhance user experience, and streamline backend processes.
Key highlights:
- Mentored 500+ developers/students on real-world coding challenges.
- Supported 100+ clients in fixing, improving, and extending their web applications.
- Known for the ability to quickly onboard to any codebase and deliver impactful results fast.
Joined the team at the early stage of the startup, contributing to the MVPs of the product by collaborating closely w...
Joined the team at the early stage of the startup, contributing to the MVPs of the product by collaborating closely with designers and backend engineers. Built the majority of the mobile web from scratch, iterating rapidly to deliver functional, user-focused features.
Introduced TypeScript and TDD to improve maintainability and code quality, while helping the growing team improve communication and task assignment processes. Leveraged my experience to guide technical decisions and accelerate development in a fast-changing environment
Developed high-traffic e-commerce websites on the Vtex platform, focusing on critical areas such as checkout ...
Developed high-traffic e-commerce websites on the Vtex platform, focusing on critical areas such as checkout and other sensitive modules, which required deep technical knowledge of the platform. Collaborated closely with Product to deliver seamless user experiences by integrating multiple data sources.
Led initiatives to improve maintainability and efficiency across client projects, creating reusable templates and standardizing repeated structures. These improvements were applied across 10+ existing client stores and continued to be used in all new stores, enabling faster iterations and more consistent results.
Introduced modern practices and technologies including ES6, Sass/SCSS, React, and Angular at a time when these were not yet widely adopted, often implementing polyfills and workarounds to ensure compatibility while improving code quality and team productivity. Built different desktop applications with ElectronJS to optimize internal workflows.
After one year, selected as Frontend Area Lead alongside two colleagues, acting as a reference point for best practices and technical guidance within the team.
Key highlights:
- Specialized in Vtex checkout and critical modules, handling complex and sensitive systems.
- Standardized reusable structures applied to 10+ stores and adopted in all new client projects.
- Introduced cutting-edge frontend technologies, implementing polyfills and advanced solutions to overcome early adoption challenges.
- Built ElectronJS desktop applications to optimize internal workflows.
- Recognized as Frontend Area Lead for mentoring and technical guidance.