Senior Vanilla JavaScript Developer

Proactiviti is a U.S.-based technology consulting and nearshore staffing firm that helps organizations scale with top-tier technology talent across Latin America. Our professionals work directly with North American clients, delivering high-quality software solutions while collaborating seamlessly across distributed teams and U.S. time zones.

Role Overview
We are seeking a Senior Vanilla JavaScript Developer to design, build, and optimize highly interactive web applications using core JavaScript without heavy reliance on frontend frameworks. This role requires deep expertise in JavaScript fundamentals, browser APIs, DOM manipulation, performance optimization, and modern web development practices. The ideal candidate is a self-driven engineer who can work directly with client stakeholders, contribute to architectural decisions, and deliver scalable, maintainable solutions in a fast-paced environment.

Key Responsibilities

• Design and develop large-scale, framework-agnostic web applications and reusable UI components using Vanilla JavaScript (ES6+).
• Write clean, maintainable, and efficient code leveraging modern JavaScript, semantic HTML5, and advanced CSS3 practices.
• Optimize application performance, accessibility, responsiveness, and Lighthouse scores through efficient DOM operations and memory management.
• Integrate frontend applications with REST APIs, WebSockets, and backend services.
• Collaborate closely with product managers, designers, backend engineers, and client stakeholders to deliver high-quality solutions.
• Conduct code reviews, mentor junior developers, and promote engineering best practices.
• Implement automated testing strategies and contribute to CI/CD workflows to ensure reliability and quality.
• Troubleshoot complex browser compatibility, performance, and scalability issues.

Required Qualifications

• 5+ years of professional frontend development experience.
• Expert-level proficiency in Vanilla JavaScript (ES6+).
• Deep understanding of the DOM, event handling, closures, scope, prototypes, asynchronous programming, and the JavaScript event loop.
• Strong experience with semantic HTML5, responsive design, and advanced CSS3 methodologies.
• Experience integrating frontend applications with RESTful APIs and real-time communication technologies.
• Familiarity with modern build tools such as Webpack, Babel, Rollup, or Vite.
• Proficiency with Git and collaborative development workflows.
• Strong English communication skills and experience working with distributed teams.
• Ability to work independently while collaborating effectively with U.S.-based clients and stakeholders.

Preferred Qualifications

• Experience with Web Components and browser-native UI architectures.
• Knowledge of TypeScript and Node.js.
• Experience with automated testing tools such as Jest, Playwright, or Cypress.
• Familiarity with cloud-based environments and CI/CD pipelines.
• Previous experience working in consulting, staff augmentation, or client-facing environments.

What Success Looks Like

• Delivering performant, scalable, and maintainable web applications.
• Collaborating effectively with cross-functional teams and client stakeholders.
• Driving technical excellence through code quality, mentorship, and best practices.
• Contributing to successful project outcomes while maintaining a strong focus on user experience and business objectives.