Kristian Lonergan

Senior Frontend Developer

Professional Summary

Senior Frontend Developer with over 10 years of experience building modern web applications. Currently acting as a line manager and code owner of two key applications at Propylon. Specialising in React, TypeScript, and modern frontend tooling, with a strong focus on code quality, mentorship, and delivering reliable, user-centred products through AI-assisted workflows.

Technical Skills

Frontend:React, TypeScript, JavaScript, HTML5 / CSS3, Next.js, Tailwind CSS, Material UI

State Management:Zustand, Redux, React Query, Context API

Testing:Playwright, Vitest, Jest, React Testing Library, Cypress

Tools & Workflow:Git, Vite, Storybook, Figma, CI/CD, Office.js, Cursor, Claude Code

Leadership & Delivery:Line Management, Code Ownership, Code Reviews, Technical Mentorship, Contractor Oversight, Agile / Scrum

Work Experience

Propylon

January 2024 - Present

Senior Frontend Developer

Code owner of the Request System (web) and its mobile application, overseeing architecture and feature delivery
Acting line manager with responsibility for team members and oversight of external contractors
Lead bi-weekly code reviews and provide technical mentorship across the frontend team
Migrated the E2E test suite from Cypress to Playwright, improving reliability and speed
Develop Microsoft Word add-ins with Office.js and React; drive frontend best practices and documentation

Rezexe

March 2020 - December 2023

Senior Frontend Developer

January 2022 - December 2023

Led frontend development for a high-traffic marketplace platform using React, TypeScript, and Material UI
Architected a Next.js monitoring dashboard for AWS container health with real-time updates
Established CI/CD pipelines, code review practices, and frontend documentation standards
Designed and implemented E2E testing strategy using Cypress

Frontend Developer

March 2020 - December 2021

Built key features for a marketplace platform with React, TypeScript, and Material UI
Created a reusable component library and integrated REST APIs with Redux and React Query
Delivered comprehensive unit tests with Jest and React Testing Library

Career Break

September 2019 - February 2020

European Travel & Professional Development

Travelled across Europe, attended tech meetups, and completed online courses in modern web technologies

IBM

June 2014 - August 2019

Software Engineer

April 2017 - August 2019

Developed enterprise web applications and led migration from legacy Dojo to modern JavaScript frameworks
Built Java backend services and RESTful APIs; mentored junior developers across global teams
Created proof-of-concept applications using React and modern tooling

Software Test Engineer

June 2015 - March 2017

Designed automated test frameworks with Java and Selenium, significantly reducing manual testing effort
Maintained CI test suites and conducted performance testing to identify bottlenecks

Software Test Engineer Intern

June 2014 - May 2015

Developed and maintained automated test suites using Java and Selenium within an Agile team