100 Days of TypeScript

One project a day, for 100 days. You start by building an M-Pesa confirmation text in your terminal and finish with an AI agent plugged into an app you built yourself.

Every day ships with tests. You run npm test and the tests tell you when you got it right, instead of you comparing your code to someone else's solution.

No JavaScript needed first. Node 24 runs TypeScript files directly, so you write TypeScript from Day 1.

Check your Node version:

node --version

You want v24 or higher. Older versions cannot run .ts files directly, and every day here depends on that.

git clone git@github.com:sagebeme/100-Days-of-TypeScript.git
cd 100-Days-of-TypeScript
npm install

Prefer pnpm? pnpm install works too, and every npm run ... / npm test command below works as pnpm run ... / pnpm test. The repo's lockfile is npm's (package-lock.json), so a pnpm-lock.yaml stays on your machine: .gitignore keeps it out of commits.

If you move the project between Windows and Linux or macOS, run the install again on the new system. Some tools download a different native binary for each one, so a node_modules folder made on Windows won't run tests on Linux.

Then start Day 1:

cd phase-1-terminal/day-001-mpesa-sms

Read the README.md in that folder, write your code in starter/, and run the tests.

The site/ folder is a website for the course: a landing page, the full syllabus, and a lesson viewer that shows each day's README with a checklist that saves your progress in your browser. Run it locally:

npm run site

It opens http://localhost:8000/site/. The site is plain static files that read the READMEs straight from the day folders, so there's nothing to build. After adding or renaming a day, refresh its list of days with npm run site:data. npm run site:check fails if the list is out of date.

To put it online, import the repo into Netlify or Vercel. netlify.toml and vercel.json are already set up: there's nothing to install or build, and / goes to /site/. Or turn on GitHub Pages for the main branch and open /site/.

Every day is a folder that looks like this:

day-001-mpesa-sms/
├── README.md            what to build, and the steps to get there
├── starter/             your code goes here
├── solution/            look after you've tried it
└── mpesa-sms.test.ts    the tests that say when you're done

The routine:

1. Watch the video for that day, linked in the day's README.
2. Read the brief. It says what the finished project does.
3. Write your code in starter/.
4. Run the tests until they pass.
5. Compare with solution/ once yours works. There's always another way to write it.

Run one day's tests:

npm test -- day-001

Run everything you've done so far:

npm test

From Day 30, projects run in the browser. Start a dev server for that day's starter/ folder and open the address it prints (usually http://localhost:5173):

npm run dev -- phase-3-browser/day-030-split-the-bill/starter

The tests still run with npm test. They use a pretend browser, so you don't need one open.

100 days in 8 phases. Each phase ends with a bigger project that uses everything before it.

From Phase 5 on, one app grows with you: an event ticketing platform. You build its API, put a web app on top, then hand it to an AI agent.

Days 81 to 100 have no build-along video. You get a short brief and a test suite, the way real work arrives.

The projects come from things people actually care about: games, music, football, sneakers, street food, side hustles. Each one has a Nairobi flavour, from matatu routes to M-Pesa payments, so the code you write looks like the place you live in. You don't need to be Kenyan to follow any of it.

Node runs TypeScript by removing the types and running what's left. It never rewrites your code. That means enum, which needs code generated at runtime, fails to run:

SyntaxError [ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX]: TypeScript enum is not supported in strip-only mode

Use a plain object instead, which works everywhere and gives you the same safety:

const Fare = { Peak: 120, OffPeak: 80 } as const;
type Fare = typeof Fare[keyof typeof Fare];

Day 27 goes into this properly. Until then, just avoid enum.

• Phase 1: Terminal foundations (Days 1–14)
• Phase 2: Modelling with types (Days 15–28)
• Phase 3: Browser and games (Days 29–42)
• Phase 4: Talking to the internet (Days 43–54)
• Phase 5: Backend with Node (Days 55–66)
• Phase 6: Full-stack React (Days 67–74)
• Phase 7: AI in TypeScript (Days 75–80)
• Phase 8: Portfolio (Days 81–100)

Tick a phase off when its tests pass. Commit your work daily: in three months you'll want to see how far you came.

1. Read the error. TypeScript errors say which line and which type. That's usually the whole answer.
2. Re-read the day's README. The step you skipped is normally in there.
3. Run the tests. A failing test names what it expected and what it got.
4. Open an issue in this repo if something is wrong or unclear. That helps whoever comes next.

MIT for the code. Course materials are for learning, personal or in a classroom.