Software Engineer · Team Lead

DerekChang Han Zhe

I build fast, reliable software — and I care about the details users never notice but always feel.

available for freelancefull-stack
Get in touch
1
§01Who I am

About

I'm a software engineer who likes turning fuzzy problems into simple, dependable systems. I've worked across the stack — from database schemas to pixel-level UI — and I'm happiest when I'm shipping and learning at the same time.

Away from the keyboard, I recharge with good food, long walks, and the occasional weekend project that starts as "just a quick script" and somehow ends up a full-blown app.

§02The kind of work I do

What I've built

01

Custom internal business tools

Bespoke internal systems built around a specific business's workflow and needs.

02

Landing pages

Fast, polished marketing pages designed to convert and load instantly.

03

Third-party API integrations

Wiring apps into external services — payment gateways, maps, messaging, AI, and more — reliably and securely.

04

Telegram mini apps & bots

Full Telegram experiences — in-chat mini apps plus bots for notifications, commands, payments, and automated workflows.

05

E-commerce platforms

Online storefronts with carts, checkout, secure payments, and order management.

06

Fitness membership apps

Membership apps for gyms and studios with plans, class booking, and check-ins.

07

Travel booking systems

Booking platforms for activities, tickets, and experiences with instant confirmation.

08

Restaurant & club membership apps

Loyalty and membership apps for restaurants and clubs with rewards and reservations.

09

HR platforms

Systems for managing employees, attendance, leave, and payroll in one place.

10

Fintech & e-wallet apps

Digital wallets and payment apps for transfers, top-ups, and everyday spending.

11

Cryptocurrency trading platforms

Real-time crypto trading with live market data, order books, charts, and secure wallets.

12

Gaming platforms

Game aggregator platforms that connect multiple providers into one unified catalog, wallet, and player experience.

13

Security & privacy apps

Privacy-first mobile apps, including tools to hide and lock apps on iOS.

§03What I work with

Skills

Languages

  • TypeScript
  • JavaScript
  • Python
  • Java
  • C++
  • C#
  • PHP
  • Swift
  • Kotlin
  • Dart
  • SQL
  • Bash
  • HTML
  • CSS
  • Objective-C

Frontend

  • Next.js
  • React
  • Nuxt
  • Vue
  • Redux
  • Zustand
  • React Query
  • Tailwind CSS
  • Sass/SCSS

Backend

  • NestJS
  • Fastify
  • Express
  • Node.js
  • Django
  • GraphQL
  • REST APIs
  • WebSockets
  • SSE

Mobile

  • iOS Native
  • Flutter
  • Expo
  • React Native
  • App Store Submission

Databases

  • MongoDB
  • PostgreSQL
  • MySQL
  • SQLite
  • Redis
  • Firebase
  • Supabase
…and more, always leveling up.
// unlock the rest when we work together
§04Off the clock

A little fun

Random factclick to roll

“Simplicity is the ultimate sophistication.”

Psst…

There’s an easter egg hidden on this page. Old-school gamers know the code. ↑↑↓↓…Needs a keyboard — open this site on a computer to try it.

terminal
Welcome to derek.sh
Type 'help' to see what I respond to.
derek@web ~ %