The TypeScript compiler, `tsc`, turns `.ts` files into JavaScript that a browser or Node.js can execute. It checks code against JavaScript rules and TypeScript features such as static types, then removes TypeScript-only syntax from the emitted JavaScript. The runtime executes that JavaScript, not the TypeScript source. section 5.4 section 2.6
Compile a small project
In `tsconfig.json`, set `compilerOptions` to `{ "target": "ES2022", "rootDir": "./src", "outDir": "./dist" }`. Put `index.ts` in `src`, run `tsc` from the project folder, then run `node dist/index.js`. Edit the `.ts` file rather than the generated `.js` file: the next compilation overwrites output in `dist`. section 2.2.2 section 2.2.4
Configuration controls what the compiler reads, checks, and writes:
- Use `files`, `include`, or `exclude` to select source files; run `tsc --listFiles` to inspect the selection, including type declarations. section 5.4
- Set `target` for the JavaScript version required by the runtime. With an `ES5` target, an arrow function becomes a function expression and `let` becomes `var`. section 5.6
- Select a compatible module format for multi-file applications. CommonJS and ECMAScript module output have different runtime requirements; ECMAScript modules in the Node.js example also require project configuration and a `.js` import extension. section 5.8
- Enable `declaration` to generate `.d.ts` files that expose inferred types alongside JavaScript output. section 7.2.2
A reported error can still produce JavaScript
For `function printMessage(msg: string) { console.log(msg); }`, the call `printMessage(100)` produces a type-mismatch error. By default, `tsc` still emits JavaScript containing the call. Set `"noEmitOnError": true` in `compilerOptions` to stop new output when errors are detected. section 5.5.1
For repeated edits, watch mode recompiles changed TypeScript files. It does not itself rerun the resulting program; `tsc-watch` can execute `node dist/index.js` after a successful compilation. The compiler is a build-time checker and translator, while Node.js or a browser remains responsible for running the application. section 5.10 section 5.0
