Senior UI Developer – (ReactJS / NestJS)

KSTACK; São Paulo; Hybrid; BRL 240,000 - 360,000; Full time

Job summary

KSTACK in Sao Paulo, Brazil, seeks a Senior UI Developer to lead front-end development with React.js, Next.js, NestJS, and TypeScript. You will build scalable, high-performance web apps, write tests, and collaborate with design and backend teams to deliver polished user experiences.

The role requires mentoring, participating in code reviews, and staying updated on frontend trends to drive engineering excellence within the team.

Qualifications

• 10+ years of overall software development experience.
• Strong expertise in React.js and NestJS.
• Proficiency in Next.js, TypeScript, and modern JavaScript (ES6+).
• Hands-on experience with unit and automated testing tools and frameworks (Jest, Mocha, Cypress).
• Strong understanding of HTML5, CSS3, Sass/SCSS, and responsive web design.
• Familiarity with state management libraries such as Redux, Zustand, or Recoil.
• Experience integrating applications with RESTful APIs and GraphQL.
• Knowledge of CI/CD pipelines and version control with Git, GitHub, and GitLab.

Responsibilities

• Design, develop, and maintain scalable front-end applications using React.js and NestJS.
• Write clean, well-documented code with TypeScript.
• Implement and maintain unit tests with Jest, Mocha, and Cypress.
• Optimize performance, scalability, and responsiveness of apps.
• Collaborate with UX/UI designers, back-end developers, and product owners.
• Mentor junior developers and participate in code reviews and agile ceremonies.
• Stay current with front-end tech and best practices across the team.

Skills

React.js

NestJS

Next.js

TypeScript

Unit testing

JavaScript (ES6+)

HTML5/CSS3

Redux

Zustand

Recoil

REST/GraphQL

CI/CD

Git/GitHub/GitLab

Education

Bachelor’s or Master’s degree in Computer Science/Engineering or related field

Tools

Jest

Mocha

Cypress

Job description

Location: São Paulo, Brazil — Hybrid

Job Description

We are seeking a highly skilled and experienced Senior UI Developer with a strong background in React.js, Next.js, NestJS, TypeScript, and unit testing. The ideal candidate has a proven track record of building scalable, responsive, and high-performance web applications.

This role requires a collaborative mindset, strong attention to detail, and the ability to take ownership of UI development initiatives from concept through implementation.

Key Responsibilities

• Design, develop, and maintain modern, scalable front-end applications using React.js and NestJS.
• Write clean, efficient, maintainable, and well-documented code using TypeScript.
• Implement and maintain unit tests using frameworks such as Jest and React Testing Library to ensure code quality and reliability.
• Optimize applications for performance, scalability, responsiveness, and overall user experience.
• Partner closely with UX/UI designers, back-end developers, and Product Owners to deliver seamless user experiences.
• Mentor junior developers and review their work to ensure adherence to engineering best practices and coding standards.
• Participate actively in code reviews, architectural discussions, and Agile ceremonies, including sprint planning and retrospectives.
• Stay current with front-end technologies, frameworks, and industry trends to promote innovation and engineering best practices across the team.

Required Skills & Qualifications

• 10+ years of overall software development experience.
• Strong expertise in React.js and NestJS.
• Proficiency in Next.js, TypeScript, and modern JavaScript (ES6+).
• Hands‑on experience with unit and automated testing tools and frameworks, such as Jest, Mocha, and Cypress.
• Strong understanding of HTML5, CSS3, Sass/SCSS, and responsive web design.
• Familiarity with state management libraries such as Redux, Zustand, or Recoil.
• Experience integrating applications with RESTful APIs and GraphQL.
• Knowledge of CI/CD pipelines and version control platforms such as Git, GitHub, and GitLab.
• Excellent problem-solving skills and strong attention to detail.
• Strong verbal and written communication skills, with the ability to collaborate effectively across teams.

Education

• Bachelor’s or Master’s degree in Computer Science, Engineering, or a related field.