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Jason Yu

Software Engineer • Tech Speaker

🧑‍💻 Work Experience

🍡 Fishball Ltd (Founder)

2025 - Present

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

📱 Mobile Apps

• 🇬🇧 Ace It: Life in the UK Test
  • 💻 React Native, TypeScript
  • A study app for the UK Citizenship Test.
• ♠️ Big2Cal
  • 💻 React Native, TypeScript
  • Score-tracking app for the popular Hong Kong card game Big2.
• ⌚️ WearDa Metronome
  • 💻 Jetpack Compose, Kotlin
  • A WearOS vibrating metronome (~1.2k MAU, >5k downloads).

🌐 Web Apps

• 🀄️ mjcal.app
  • 💻 React, TypeScript
  • Mahjong score-tracking app with analytics and stats.

😻 Open Source Projects

• @fishballpkg/linkz
  • Config-driven static site generator powering my website.
  • Generates a linktree-like page with markdown support.
• @fishballpkg/acme
  • Minimalistic, zero-dependency, pure TypeScript ACME client.
  • Uses the ACME standard for generating TLS certificates.

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.
• 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*.
• Improved error detection and component testing DX.
• Advocated for the “rule of least power” as a coding principle.
• Led migration from vanilla TypeScript to Vue.js.

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.

🎤 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

🛠️ Open Source & Side Projects

• 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

✍️ Articles

📖 All articles availabel 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.