Jonas Mazza Fernando
Verified Expert in Engineering
Front-end Engineer and Developer
Limeira - São Paulo, Brazil
Toptal member since December 25, 2024
Jonas is a senior front-end engineer with 6+ years of experience developing scalable, dynamic web applications using modern technologies like TypeScript, React, and Next.js. He is skilled in building customer-facing platforms and internal tools, from static web pages to highly dynamic interactive apps. Jonas is passionate about delivering value through maintainable and performant code.
Portfolio
Experience
- TypeScript - 6 years
- JavaScript - 6 years
- React - 6 years
- Storybook - 6 years
- React Testing Library - 4 years
- Tailwind UI - 3 years
- Playwright - 3 years
- Next.js - 3 years
Availability
Preferred Environment
TypeScript, JavaScript, React, Next.js, Web, Front-end
The most amazing...
...challenge I've tackled is owning the front-end development for a dynamic SPA in JavaScript React, enhancing maintainability while delivering valuable features.
Work Experience
Senior Front-end Engineer
Toptal
- Created and maintained revenue-driven Toptal.com public pages, statically generated via a custom SSR engine using Node.js and React, focusing on Core Web Vitals, performance, SEO, accessibility, and mobile optimization.
- Led the engineering planning and built a successful PoC to standardize event tracking via Google Analytics 4, implementing contextual data tracking by default within atom-level UI components.
- Collaborated with PMs and stakeholders to manage feature scope and delivery timelines, aligning efforts with team practices and prioritizing efficient task breakdown and critical feature delivery.
- Worked cross-functionally with designers and back-end engineers to ensure seamless integration of features, performing thorough code reviews and maintaining high code quality standards.
- Enhanced QA processes by implementing visual regression, unit, and integration testing, helping identify bugs early and improving public pages' overall stability and performance.
Front-end Engineer
Encora
- Developed and maintained highly dynamic React SPAs for internal applications and white-label platforms for a leading British telecoms company. Took ownership as the sole front-end engineer working on front-end development.
- Developed and maintained an API gateway that connected multiple apps and services. This gateway handled user authentication, authorization, app routing, and service mocking for streamlined local development.
- Maintained and modernized a legacy Node.js back-end-for-front-end server to ensure seamless integration between services and improve overall system stability.
- Developed internal tools to boost developer productivity, including a fake authentication tool for easy app testing, a service status monitor, and a browser-based terminal for staging environment access.
- Contributed to creating a centralized cross-product UI library used across multiple projects, collaborating with the team to establish reusable components.
- Conducted numerous hiring interviews for software engineering roles, participating as a peer and lead interviewer.
- Designed and led training programs for interns, several of whom were later hired as full-time engineers.
Experience
Event Tracking Standardization with Google Analytics 4
This proof of concept, built with React and TypeScript, was well-received by stakeholders and established a foundation for future analytics features. The project streamlined the workflow for engineers, simplified feature adoption, and aligned with business objectives by providing detailed insights into user interactions. My collaborative approach helped ensure smooth integration with existing systems and clear documentation for future scaling.
Education
Bachelor's Degree in Electrical Engineering
Federal University of Uberlandia - Uberlandia, Brazil
Skills
Libraries/APIs
React, React Testing Library, Playwright, Node.js
Tools
Redux Toolkit
Languages
TypeScript, JavaScript, HTML, CSS, Sass, GraphQL
Frameworks
Jest, Next.js, Redux, Express.js
Platforms
Web
Storage
LokiJS
Other
Front-end, Storybook, Tailwind UI, Styled-components, XState, Google Analytics 4
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