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# Principal Frontend Engineer

- **Company:** Harnham Inc.
- **Location:** White Plains, NY, United States
- **Experience:** Expert
- **Contract:** Permanent contract
- **Skills:** Clean Code Principles, Automation of Tests, Code Review, Next.js, Strategies of Testing, TypeScript, Web Applications, ReactJS, Agentic-AI, Information Technology, Front End Software Development, Functional Programming
- **Published:** October 20, 2026
- **Apply:** https://www.juju.com/job/23_CF4991397FD0AB3C0A9D128FD263B973

## About the Role

Bachelor's degree in Computer Science, Engineering, or a related field

5+ years of experience building production web applications, including senior-level ownership

Prior experience operating at principal, lead, or staff engineer level

Expert proficiency with TypeScript and React , including server-side rendered frameworks such as Next.js

Strong understanding of functional programming concepts and immutability in modern frontend systems

Advanced knowledge of automated testing strategies and CI-driven feedback loops

## Description

The organisation builds large-scale, consumer-facing platforms used by hundreds of millions of users worldwide, with a strong focus on quality, long-term maintainability, and responsible AI-assisted development. This role sits within a financial products marketplace that partners with major financial institutions to deliver personalised consumer experiences. The position is ideal for a senior-level engineer who values engineering judgement, thoughtful architecture, and technical leadership over speed alone.

Responsibilities:

Own and uphold a high engineering quality bar across design reviews, code reviews, testing strategy, and production readiness

Collaborate closely with product, design, and engineering partners to shape solutions and evaluate technical trade-offs

Architect and build frontend-leaning, full-stack systems that are modular, composable, and resilient to change

Champion performance, reliability, and maintainability in AI-assisted development environments

Apply functional programming principles and immutability to reduce side effects and improve system clarity

Lead the effective use of AI agents for prototyping, refactoring, and exploration while ensuring production-grade outcomes

Drive a robust automated testing strategy across unit, integration, UI/component, and end-to-end layers

Provide technical leadership through mentorship, delegation, and high-quality code reviews