yceffort
KO

FRONTEND ENGINEER AND WRITER

yceffort.

A record of the experience I gained by building and running things.

root@yceffort.kr GitHub

EXPERIENCE AND CONTRIBUTIONS

From building services to the ground a team works on.

I have built and run software across many domains since 2014. I have led a frontend team and built libraries and tools shared by many services. I pass on what I learned through books, writing, and open source.

Frontend engineer, currently employed

Building services
React, TypeScript, Next.js
Operations and performance
Node.js, Kubernetes, web performance
Team foundations
Shared libraries, CLIs, code review

Experience

Experience from where I work now and the places I have worked before.

  1. KakaoPay Securities

    2026.03 to present

    Frontend Engineer, Home team

    Building the stock home screens and making them faster

    • Built the securities home in the KakaoPay app and the stock home in the KakaoBank app
    • Wrote a WebSocket library
    • Cut FCP by 44%, downloaded JS by 38%, and CPU time in the first 5 seconds by 30% on the home screen (mobile lab measurement) by reassembling an external SDK, cleaning up bundles, and improving rendering
    • Restored a required external SDK from its source maps and reassembled it without touching its logic, cutting the event sending entry by 72% (gzip)
    • Removed frame drops from a framer-motion banner, ported number-flow to older browsers, and moved its animation to the compositor thread

    React, TypeScript, Next.js, Turbopack

  2. NAVER Financial

    2020.09 to 2026.03

    Frontend Engineer, Assets & Membership FE Lead → Card FE Lead / Shared Development TF Lead

    Led a frontend team of up to 14 people, building financial services and the shared foundation of the frontend organization

    • Led the move from a single CRA app to 20-plus SSR services on Koa and Next.js, so a failure stays inside one service and each service can deploy on its own, more often
    • Led the shared packages used by those 20-plus services (@mydata, @financial, @financial-auth, @pie) and set up how they are published to the registry
    • Led bundle size work that cut the _app chunk shared by every page by 345 kB (51%) and 110 pages by 1.17 MB in total, bringing the average initial load from 2.6 s to 1.4 s
    • Started the NaverPayDev open source program and led publishing and maintaining the team's shared packages
    • Built hidash, a lodash replacement
    • Built mobile financial services including MyData, member authentication, and the card tab
    • Built and maintained a state management library, the design system, a project scaffolding tool, Node.js CLIs, and MCP servers for everyday productivity
    • Led code review and mentoring on the team, ran intern hiring interviews, and created and ran hiring assignments and intern practice assignments

    React, TypeScript, Next.js, Node.js, Kubernetes, pnpm, Turborepo

    See the public packages

  3. Triple

    2019.05 to 2020.08

    Frontend Engineer

    Built a travel web service that runs from discovery through booking and payment

    • Built and operated global city search and flight ticket sales
    • Migrated the payment service and shared components from JavaScript to TypeScript
    • Built a one-to-one chat service between sellers and customers

    React, TypeScript, Next.js, Koa, Docker, Amazon ECS

  4. Kakao

    2016.09 to 2019.05

    Software Engineer

    Built and operated the frontend and server of Kakao Together, a donation platform

    • Migrated a legacy AngularJS application to Angular
    • Built admin tools and operated the Ruby on Rails server alongside them

    Angular, TypeScript, Ruby on Rails, MySQL, Redis

  5. Samsung SDS

    2014.03 to 2016.06

    Software Engineer

    Built global healthcare solutions and proofs of concept for new technology

    • Built an EHR solution for overseas hospitals and a nursing ward service
    • Built iOS beacon based indoor navigation and a blockchain PoC for a financial client
    • Validated data consistency and integrity with Python

    Delphi, Oracle DB, Spring, JavaScript, Python

Publications

WRITING NOW

Who Learns the Judgment That Remains An essay on developers, judgment, and learning in the age of AI. Working title, in progress (Korean).

Node.js Deep Dive A technical book on how Node.js works inside, from V8 and libuv to module loaders, memory, networking, and production environments. Working title, in progress (Korean).

Open source

  • Developer tool

    @yceffort/coldpath

    A Rust CLI that traces JavaScript bundle bytes back to their original sources with source maps and V8 coverage. It separates code that runs on load from code that runs only on interaction, and produces bundle treemaps and pull request comparisons. Analysis runs offline, without Node.js or a browser.

    • #rust
    • #source-map
    • #v8-coverage
  • Fork and extension

    @yceffort/number-flow

    A fork of barvian/number-flow that makes its number animations work in older browsers and webviews. It keeps the original API, adds a fallback engine built on requestAnimationFrame, and was verified on real legacy browsers.

    • #typescript
    • #javascript
    • #react
    • #web-component
  • Webview debugging

    @yceffort/storage-inspector

    A Lit web component for inspecting and editing localStorage and sessionStorage inside a webview. Each key gets a description and type from a schema, and values are validated as you edit them.

    • #typescript
    • #lit
    • #web-component
  • Developer tool

    @yceffort/rust-markdownlint

    A Markdown linter written in Rust that aims to be compatible with markdownlint-cli2. Its diagnostics and auto-fixes were checked against the original tool, and it runs on the repositories I maintain.

    • #rust
    • #rayon
  • macOS app

    yc.clipboard

    A macOS menu bar app for searching and reusing your clipboard history, including text, images, and files. It supports pinning, previews, and pasting back into the previous app.

    • #swift
    • #swiftui
    • #appkit

Beyond work

  • 2024

    Talk at DAN24

    Spoke about optimizing the bundle size of web services.

  • 2021.01 to 2021.12

    SSAFY mentor

    Supported young developers at the Samsung Software Academy For Youth by answering programming questions and writing columns.

  • 2018 to present

    Tech blog yceffort.kr

    I build and run this blog myself, and write about framework internals, performance and operations, developer tools, and working with AI.

  • 2016.03 to present

    Board member, JUMP (nonprofit)

    I help with work automation on Google Cloud Platform and with programming education.

Education

  • 2018.03 to 2020.02

    KAIST

    M.S., Graduate School of Management of Technology

    Highest Honors, GPA 4.23 / 4.3

  • 2007.03 to 2014.02

    Dongguk University

    B.A. in International Trade, double major in English Interpretation and Translation