Setting Up an Express + TypeScript Project

Before writing any routes, get a minimal Express + TypeScript project compiling and running.

Install dependencies

npm init -y
npm install express zod
npm install -D typescript @types/express @types/node tsx
npx tsc --init

express and zod are runtime dependencies, your server actually needs them once it's running. typescript and @types/express/@types/node are dev-only, they exist purely to type-check your code before it ships. tsx runs .ts files directly during development without a separate build step.

Key tsconfig.json options

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "commonjs",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "outDir": "dist"
  }
}

"strict": true turns on every strict type-checking flag at once (including the unknown-forcing narrowing rules from the last course), it's the setting that makes TypeScript actually catch bugs instead of just documenting types. Leave it on for anything beyond a throwaway script.

A minimal server

import express from 'express';

const app = express();
app.use(express.json()); // parses JSON request bodies into req.body

app.get('/health', (_req, res) => {
  res.json({ status: 'ok' });
});

app.listen(3000, () => console.log('Server running on http://localhost:3000'));

The leading underscore in _req is a convention (not a language feature) for "this parameter is required by the function signature but isn't used in the body," it keeps an unused-parameter lint rule quiet without disabling the check entirely.