Jason Yu

Principal Frontend Engineer • Tech Speaker • Open Source Contributor

📧 me@ycmjason.com • 📍 London, UK

Passionate software engineer with 8+ years of experience building scalable frontend architectures, leading TypeScript migrations, and empowering developer communities through open source and public speaking. Creator of 14k+ download mobile apps and innovative dev tools.

🧑‍💻 Work Experience

Boltzbit (Principal Frontend Engineer)

2025 - Present

Architected a scalable frontend monorepo to facilitate seamless integration with external teams.
Spearheaded the migration to TypeScript, improving code reliability and developer experience.
Led the frontend architecture for a no-code, AI-empowered app builder:
- Developed a widget registry enabling users to compose apps via modular components.
- Created a Widget SDK to support third-party extensions and ecosystem growth.

🍡 Fishball Ltd (Founder)

2025 - Present

Building multiple apps, SaaS, and open-source projects:

📱 Mobile Apps

⌚️ WearDa Metronome
- 💻 Jetpack Compose, Kotlin
- A WearOS vibrating metronome with >14k downloads.
🇬🇧 Ace It: Life in the UK Test (Android, iOS)
- 💻 React Native, TypeScript
- A study app for the UK Citizenship Test.
♠️ Big2Cal (Android, iOS)
- 💻 React Native, TypeScript
- Score-tracking app for the popular Hong Kong card game Big2.
🀄️ 麻雀計分器 mjcal (Android, iOS)
- 💻 React Native, TypeScript
- A Cantonese mahjong scoring calculator with customizable house rules, automatic point calculation, and multi-round game tracking.

🌐 Web Apps

🀄️ mjcal.app
- 💻 React, TypeScript
- Mahjong score-tracking app with analytics and stats.
🔗 dynm.link
- 💻 React, TypeScript, Cloudflare Workers + D1 + R2
- A “microlinks” platform — create redirects, hosted markdown pages, file links, bio pages, and more. Custom domains coming soon.

Bloomberg LP (Senior TypeScript Engineer)

2023 - 2025

Led migration to TypeScript strict mode
- Increased visibility of strict mode errors:
  - Developed @ts-expect-strict-error, a TypeScript Language Service Plugin, showing strict mode errors in IDEs (without affecting tsc).
  - Allowed suppressing errors with @ts-expect-strict-error-next-line.
- Prevented new strict mode errors:
  - Built a CLI tool leveraging @ts-expect-strict-error.
  - Enforced checks via a new CI step, blocking PRs with unmarked strict errors.
- Reduced existing strict mode errors:
  - Introduced Grafana dashboards to track progress and a leaderboard to gamify error elimination.
  - Eliminated 15% of 10k errors in the first month.
  - Reduced technical debt by 1,500+ strict mode violations through team collaboration.
Defined best practices and patterns for scalable TypeScript code.

Attest Technology Limited (Frontend Engineer)

2019 - 2023

Developed an A* algorithm-based SVG line drawing module for signature capture.
Improved error detection and component testing DX, reducing bug reports by 40%.
Advocated for the “rule of least power” as a coding principle.
Led migration from vanilla TypeScript to Vue.js, modernizing the tech stack.

The Hut Group (Full Stack Engineer)

2017 - 2019

Built a vanilla JavaScript component framework.
Founded & led “JS Club” to promote modern JavaScript practices.
Developed a CLI tool to improve developer workflows.

🎬 YouTube

Technical Talks & Tutorials

TRY {} CATCH {} ‒ FIXED! (with a surprisingly old trick)
- Analyzed limitations in standard JavaScript error handling and demonstrated an IIFE-based pattern to improve code integrity and type inference.
7 MODERN IIFE TRICKS IN 10 MINUTES
- Presented seven practical use cases for Immediately Invoked Function Expressions (IIFE) in modern development, including async operations, variable scoping, and encapsulation.
Your code: powerful, but not clean. Here’s why
- Applied the “Rule of Least Power” to software engineering, advocating for “depowering” code conventions to enhance long-term readability and maintainability.
Introducing ts-migrating: Upgrade TSConfig Progressively
- Demonstrated ts-migrating, an open-source tool designed to help developers upgrade strict TypeScript compiler options progressively across large codebases.

🛠️ Open Source & Side Projects

ts-migrating
- A plugin enabling progressive upgrades to stricter compilerOptions (e.g., strict, noUncheckedIndexedAccess, erasableSyntaxOnly) by allowing problematic lines to fall back to legacy settings.
@fishballpkg/acme
- A zero-dependency, minimalist ACME client in TypeScript designed to simplify certificate generation.
- Leveraged modern web standards (e.g., Web Crypto API) and implemented a custom ASN.1 Encoder using low-level Uint8Array manipulation. 🤓
one-page-pdf
- A CLI tool using Puppeteer to render webpages into single-page PDFs.
- Used to generate the PDF version of this very CV.
diary.ycmjason.com
- AI-powered diary using LLM, inspired by Tom Riddle’s diary.
- Find out more on GitHub
Keyboard-Keyboard
- Web-based musical keyboard using Web Audio API.
- Find out more on GitHub
Perfect Colour
- Vision quiz testing ability to recognize RGB values.
- Find out more on GitHub

🎤 Public Speaking

Live Coding: Recreating Vue’s Reactivity System
- 📆 Oct 2023
- 📍 Vue.js Slovenia Meetup
- ▶️ Recording
Vue 3 Reactivity Reimagined
- 📆 Nov 2019
- 📍 Vue.js London Meetup
- ▶️ Recording
Live coding: The new Composition API
- 📆 Oct 2019
- 📍 Vue.js London Conference
- ▶️ Recording
Vue without View - An Introduction to Renderless Components
- 📆 Jun 2019
- 📍 Vue.js London Meetup
- ▶️ Recording
Building a Simple Virtual DOM from Scratch
- 📆 Nov 2018
- 📍 Manchester Web Meetup
- ▶️ Recording

✍️ Articles

📖 All articles available at dev.to/ycmjason

Here are some hand-picked highlights:

Typing Partially Applicable Functions in TypeScript
- 📆 Jun 2023
- 🔗 Read
Detecting Barcodes from the Browser
- 📆 Nov 2021
- 🔗 Read
Writing Cleaner Code with the Rule of Least Power
- 📆 Apr 2020
- 🔗 Read
Building a Simple Virtual DOM from Scratch
- 📆 Dec 2018
- 🔗 Read

🎓 Education

Imperial College London

2014 - 2017 • BEng Computing

Courses: Haskell, Java, C, C++, Prolog, Python, AI, Operating Systems, Compilers, Networking.

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