PhyongNam is available for hire
Hire PhyongNamPhyongNam Kim
Verified Expert in Engineering
Full-stack Developer
Yorba Linda, CA, United States
Toptal member since September 19, 2019
Bio
Kim is an accomplished full-stack developer with a strong focus on front-end development. He has built a high-impact application used by major brands such as KFC, Alaska Airlines, and Delta Airlines and a SaaS platform supporting millions of monthly active users. Known for his professionalism and sense of responsibility, Kim thrives both independently and in collaborative team environments.
Portfolio
HOVER
React, Node.js, Next.js, ECMAScript (ES6), Chakra UI, React Query, GraphQL...
GeneDx
React, TypeScript, Styled-components, Unit Testing, Integration Testing, Jest...
Tellimer
HTML, CSS, Tailwind CSS, Data Visualization, Serverless, SCSS, ECMAScript (ES6)...
Experience
- Front-end - 7 years
- React - 6 years
- JavaScript - 5 years
- TypeScript - 4 years
- React Native - 3 years
- Full-stack - 3 years
- Next.js - 3 years
- Node.js - 3 years
Availability
Full-time
Preferred Environment
Visual Studio Code (VS Code), MacOS
The most amazing...
...thing I’ve developed is a SaaS platform that supports millions of monthly active users.
Work Experience
Senior Full-stack Developer
2023 - 2025
HOVER
- Built a React-based design system with Storybook. Replaced 200+ legacy components and improved UI consistency.
- Rebuilt legacy WordPress site with React, Node.js, TypeScript, and Next.js, improving SEO, cutting load time by 40%, and increasing traffic by 30%.
- Created an AI-driven article tool using ChatGPT APIs with React, Node.js, Supabase, and AWS. Reduced editorial workload and increased content output by 60%.
- Built responsive, pixel-perfect UIs from Figma, collaborating with designers and developers for smooth front-end delivery.
- Integrated Contentful and HubSpot CMS to manage dynamic content and improve content workflow.
- Applied WCAG 2.0 standards to improve accessibility.
- Set up A/B testing and monitoring with LaunchDarkly, Segment.io, and Datadog.
- Wrote unit and end-to-end (E2E) tests using Jest, React Testing Library, and Cypress to ensure stability.
Technologies: React, Node.js, Next.js, ECMAScript (ES6), Chakra UI, React Query, GraphQL, HTML, JavaScript, TypeScript, Unit Testing, E2E Testing, Jest, React Testing Library, Cypress, Webpack, Storybook, Contentful, HubSpot, A/B Testing, LaunchDarkly, Segment, Datadog, OpenAI, OpenAI API, ChatGPT, ChatGPT API, Amazon Web Services (AWS), AWS Lambda, Amazon API Gateway, Git, Figma, Search Engine Optimization (SEO), Web Accessibility, Accessibility, Front-end, APIs, REST APIs, Full-stack, GitHub, HTML5, Supabase, Server-side Rendering (SSR), SSG, AI Agents
Senior Front-end Developer
2021 - 2023
GeneDx
- Fixed 30+ bugs and launched 5+ features on legacy sites, improving UI/UX and performance and driving user growth.
- Migrated legacy AngularJS 1.6 code to React 18 incrementally, converting pages individually and managing routing.
- Developed reusable, testable React components using Jest, React Testing Library, and Playwright, improving UI consistency and user experience across projects.
- Made minor updates and bug fixes to the existing C# .NET back end to resolve issues and support ongoing development.
Technologies: React, TypeScript, Styled-components, Unit Testing, Integration Testing, Jest, React Testing Library, Playwright, ECMAScript (ES6), Next.js, C#, Angular, WordPress, Git, Bitbucket, Figma, Front-end
Senior Full-stack Developer
2019 - 2021
Tellimer
- Rebuilt UI/UX with Vue, TypeScript, Nuxt, and Tailwind CSS based on Figma designs, doubling user registrations.
- Built an AI-powered data tool with Vue, Nuxt, TypeScript, and Node.js using AWS serverless architecture.
- Built marketing email templates using raw HTML and CSS and integrated them with Mailchimp, increasing open rates by 20%.
- Improved homepage load speed by over 50% through caching and other performance optimizations.
- Implemented an onboarding process with integrated Stripe payment flow to streamline user signup and transactions.
- Developed an editor dashboard for content management, with data visualization powered by D3.js.
- Used Storybook to test UI components and streamline collaboration with designers.
- Learned new technologies quickly to meet evolving project needs.
Technologies: HTML, CSS, Tailwind CSS, Data Visualization, Serverless, SCSS, ECMAScript (ES6), TypeScript, Node.js, GraphQL, D3.js, Vue, Vue 2, Vuex, Nuxt.js, Storybook, Zeplin, HTML Email, Responsive Email Templates, Litmus, Mailchimp, Amazon Web Services (AWS), AWS Amplify, Amazon Cognito, AWS AppSync, Amazon DynamoDB, Amazon S3 (AWS S3), AWS Lambda, Payment APIs, Subscriptions, Stripe API, Git, GitLab, Front-end, APIs, REST APIs, Full-stack, HTML5, CSS3, Payment Gateways
Senior Full-stack Developer
2017 - 2019
Springshot
- Built a cross-platform React Native app used by Alaska and Delta Airlines.
- Developed a high-availability dashboard and website in React for mission scheduling and notifications.
- Implemented live chat in a React Native app and React dashboard using Socket.IO and Mattermost.
- Wrote unit and E2E tests following TDD principles using Jest, Enzyme, and Appium; integrated testing into a Jenkins CI/CD pipeline.
- Resolved challenges, including navigation-related performance issues, to improve app speed and usability.
- Implemented push notifications using FCM and APNS.
- Implemented single sign-on (SSO) using Azure AD B2C.
- Collaborated in agile teams to align work with business goals.
Technologies: React Native, React, Redux, GraphQL, Socket.IO, MongoDB, Unit Testing, E2E Testing, Test-driven Development (TDD), Jest, Enzyme, Appium, Sketch, Mattermost, Git, GitHub, Single Sign-on (SSO), Azure Active Directory B2C (ADB2C), Push Notifications, Firebase Cloud Messaging (FCM), APNs, Firebase, Cloud Firestore, CI/CD Pipelines, Jenkins, Fastlane, iOS, Xcode, Android, Android Studio, Mobile, Front-end, Full-stack
Full-stack Developer
2014 - 2017
NHN Entertainment
- Developed a scalable SaaS platform from scratch using React, Node.js, Redis, Express.js, and NGINX, serving millions of users.
- Launched an MVP for a car-sharing platform using React Native, helped secure funding, expanded globally, and later drove rapid growth to millions of users.
- Managed simultaneous high-priority projects, ensuring on-time, quality delivery.
- Developed clean, maintainable, and well-documented code to ensure long-term project sustainability and ease of collaboration.
- Collaborated with non-technical clients and stakeholders, translating complex technical concepts into actionable insights.
- Adapted to startup environments, driving fast-paced product development.
Technologies: HTML, CSS, JavaScript, React, Node.js, TypeScript, Express.js, Mocha, Chai, React Native, Redux, Sass, SCSS, Material UI, Redis, PostgreSQL, MongoDB, NGINX, Payment APIs, Subscriptions, Stripe API, Jira, Git, GitHub, Minimum Viable Product (MVP), Front-end, APIs, REST APIs, Full-stack, Mobile, HTML5, CSS3, JSON, Payment Gateways, MySQL, LocalStorage, User Authentication
Experience
Membership-based Content Platform with Millions of MAUs
https://patreon.comA membership platform with millions of MAUs that empowers content creators to run subscription services through comprehensive business tools.
I worked as a full-stack developer, focusing on writing high-quality code and following best practices to support scalability, performance, and a large user base.
I worked as a full-stack developer, focusing on writing high-quality code and following best practices to support scalability, performance, and a large user base.
React-based Design System
https://storybook.hover.toAn internal design system used across multiple websites. As a senior front-end developer, collaborating with designers and developers, I developed components while maintaining accessibility with WCAG 2.0.
Mobile App to Manage and Track Remote Teams
https://apps.apple.com/app/id1315795000An app that enables remote teams to coordinate and perform time-sensitive tasks quickly and efficiently, used by renowned enterprises such as KFC, Alaska Airlines, and Delta Air Lines.
I worked as a senior React Native developer in a mobile team, collaborating with both team members and cross-functional teams. I developed critical features, including single sign-on (SSO), offline-supported news bulletins, push notifications, live chat, and Beacon signal detection.
We utilized TDD to build a high-quality app.
I worked as a senior React Native developer in a mobile team, collaborating with both team members and cross-functional teams. I developed critical features, including single sign-on (SSO), offline-supported news bulletins, push notifications, live chat, and Beacon signal detection.
We utilized TDD to build a high-quality app.
SEO-friendly Documentation Website
https://design-system.hover.to/guides/getting-startedDeveloped a comprehensive documentation site for an internal design system using Next.js, React, Node.js, TypeScript, and Chakra UI. The platform showcases reusable components, usage guidelines, and accessibility best practices, making it easy for designers and developers to maintain consistency across products.
MVP for a Fleet-based Car-sharing Mobile App
https://play.google.com/store/apps/details?id=my.socar.flexThe company decided to expand internationally and needed the app to be redeveloped.
I developed the MVP iOS and Android app for a fleet-based car-sharing platform, which played a crucial role in helping the company secure funding and grow its operations.
The app is now one of the top car-sharing platforms in Korea.
I developed the MVP iOS and Android app for a fleet-based car-sharing platform, which played a crucial role in helping the company secure funding and grow its operations.
The app is now one of the top car-sharing platforms in Korea.
Serverless Platform for Document Analysis
https://parsel.aiA membership-based website offering AI-powered document analysis services.
As a full-stack developer, I built the platform using a serverless architecture with Vue, Nuxt.js, Node.js, and AWS services. The UI was designed to be clean and visually appealing, enhanced with smooth animations and transitions to improve user engagement. I also focused on secure authentication and scalable infrastructure for a reliable user experience.
As a full-stack developer, I built the platform using a serverless architecture with Vue, Nuxt.js, Node.js, and AWS services. The UI was designed to be clean and visually appealing, enhanced with smooth animations and transitions to improve user engagement. I also focused on secure authentication and scalable infrastructure for a reliable user experience.
Business Insight News Platform
https://tellimer.comA business insight news platform similar to Bloomberg. I was a senior Vue.js front-end developer, contributing to the news website and admin dashboard.
My responsibilities included optimizing performance, updating web pages to match new designs, adding new pages with A/B testing, and developing email templates.
My responsibilities included optimizing performance, updating web pages to match new designs, adding new pages with A/B testing, and developing email templates.
Marketing Email Templates for Business News Platform
As a senior front-end developer, I created custom marketing email templates using raw HTML and CSS for Tellimer (https://tellimer.com – a business news platform), ensuring cross-client compatibility and responsive design.
I integrated the templates with Mailchimp and used Litmus to rigorously test and optimize rendering across various email clients and devices.
This attention to detail and thorough testing significantly improved email quality and deliverability, ultimately leading to a 20% increase in open rates.
I integrated the templates with Mailchimp and used Litmus to rigorously test and optimize rendering across various email clients and devices.
This attention to detail and thorough testing significantly improved email quality and deliverability, ultimately leading to a 20% increase in open rates.
Dashboard for Business News Platform
https://engage.tellimer.comDeveloped a comprehensive dashboard that enables administrators and editors to efficiently manage and organize content for a business news platform. The dashboard features a visually polished UI and delivers actionable insights through interactive charts, diagrams, and performance metrics.
As a front-end developer, I focused on building content editing and analysis result review pages, with an emphasis on clean design, intuitive usability, responsiveness across devices, and optimized performance.
As a front-end developer, I focused on building content editing and analysis result review pages, with an emphasis on clean design, intuitive usability, responsiveness across devices, and optimized performance.
Admin Dashboard for Remote Team Management and Tracking Platform
https://webapp.springshot.comAn admin dashboard for the platform is used to manage and track remote teams, and I worked as a senior front-end developer on a dashboard project, focusing on developing the SSO and mission scheduling system.
This dashboard is for the Springshot platform, which is utilized by large companies such as KFC, Alaska Airlines, Delta Air Lines, and others.
This dashboard is for the Springshot platform, which is utilized by large companies such as KFC, Alaska Airlines, Delta Air Lines, and others.
AI-powered Article Generation Tool
At Hover, I developed an internal AI-powered article generation tool, leveraging ChatGPT APIs for content creation. As a full-stack developer, I was responsible for implementing the platform's front and back ends.
Education
2010 - 2014
Bachelor's Degree in Computer Science
Ajou University - Korea
Certifications
JANUARY 2012 - JANUARY 2015
TOEIC
Toeic
APRIL 2011 - PRESENT
Project+
CompTIA
MARCH 2011 - MARCH 2014
Security+
CompTIA
Skills
Libraries/APIs
React, Node.js, React Query, React Testing Library, REST APIs, Playwright, LocalStorage, Vue, OpenAI API, D3.js, Vue 2, Vuex, Stripe API, AWS Amplify, Socket.IO, Chai
Tools
Git, LaunchDarkly, Figma, Bitbucket, Zeplin, Litmus, Amazon Cognito, GitLab, Sketch, GitHub, Azure Active Directory B2C (ADB2C), Firebase Cloud Messaging (FCM), Fastlane, Jira, Webpack, ChatGPT, Mailchimp, AWS AppSync, Jenkins, Xcode, Android Studio, Mocha, NGINX, Mattermost
Languages
TypeScript, HTML, CSS, SCSS, JavaScript, ECMAScript (ES6), GraphQL, Sass, HTML5, CSS3, C#
Frameworks
React Native, Next.js, Jest, Cypress, Tailwind CSS, Redux, Express.js, Material UI, Nuxt.js, Appium, Angular
Paradigms
Unit Testing, E2E Testing, Object-oriented Programming (OOP), Functional Programming, Search Engine Optimization (SEO), Test-driven Development (TDD)
Platforms
Amazon Web Services (AWS), Contentful, AWS Lambda, iOS, Android, Mobile, HubSpot, Firebase, WordPress
Storage
PostgreSQL, Amazon DynamoDB, Amazon S3 (AWS S3), MongoDB, Database Structure, JSON, MySQL, Datadog, Redis, Cloud Firestore
Other
Front-end, Full-stack, Chakra UI, Storybook, A/B Testing, APIs, Styled-components, Integration Testing, Responsive Email Templates, Enzyme, Single Sign-on (SSO), Push Notifications, APNs, CI/CD Pipelines, User Management, Minimum Viable Product (MVP), Internationalization, HTML Email, Programming Languages, Software Engineering, Server-side Rendering (SSR), SSG, User Authentication, Segment, OpenAI, ChatGPT API, Amazon API Gateway, Web Accessibility, Accessibility, Data Visualization, Serverless, Payment APIs, Subscriptions, Geolocation, Payment Gateways, Supabase, AI Agents, Bluetooth
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