Setup and tsconfig — TypeScript

Where this bites you

A tsconfig.json that sets outDir but not rootDir was the usual minimal setup for years, and it is how this page showed it until October 2026. Under TypeScript 6.0 it fails: tsc reports TS5011, asking for an explicit rootDir. Because tsc still emits on error, the output also moves one folder deeper, to dist/src/index.js, so any script that runs dist/index.js breaks as well.

TypeScripttsconfig.json (without rootDir)

{
  "compilerOptions": {
    "target": "es2025",
    "module": "esnext",
    "strict": true,
    "outDir": "./dist"
  },
  "include": ["src/**/*"]
}

Shellterminal

$ tsc
tsconfig.json(6,5): error TS5011: The common source directory of 'tsconfig.json' is './src'. The 'rootDir' setting must be explicitly set to this or another path to adjust your output's file layout.
  Visit https://aka.ms/ts6 for migration information.
$ find dist -type f
dist/src/index.js

Canonical Definition

TypeScript is installed via npm, providing the tsc command-line compiler (or, as of 2026, the newer Go-based tsgo in TypeScript 7.0). A tsconfig.json file at a project's root configures compiler behavior — which files to include, which JavaScript version to target, and how strict type-checking should be — and its presence is also what most editors use to provide TypeScript-aware autocomplete and error checking.

Installing and compiling

tsc compiles .ts files down to plain .js, stripping all type annotations in the process — the output is ordinary JavaScript with no trace of TypeScript syntax left in it.

Shellterminal

$ npm install -D typescript
$ npx tsc --init          # generates a starter tsconfig.json
$ npx tsc                  # compiles every .ts file per tsconfig.json
$ npx tsc --watch          # recompiles automatically on save

A minimal tsconfig.json

strict: true enables the full family of strict type-checking rules (no implicit any, strict null checks, and more) in one flag — official TypeScript guidance recommends this for new projects, and TypeScript 6.0+ enables it by default.

TypeScripttsconfig.json

{
  "compilerOptions": {
    "target": "es2025",
    "module": "esnext",
    "strict": true,
    "outDir": "./dist",
    "rootDir": "./src"
  },
  "include": ["src/**/*"]
}

The minimal config above now includes "rootDir": "./src", which is all TypeScript 6.0 needs. With it, the build is clean and the output lands where scripts expect it. (Verified with tsc 6.0.3 on a one-file project; the Compiler page explains why the folder layout depends on rootDir.) The tsc --init command in the first section is a safe start, too: in 6.0.3 it writes a strict config with no outDir at all, so this only bites once you add an output folder.

Shellterminal

$ tsc
$ find dist -type f
dist/index.js

Running TypeScript without a separate compile step

Modern Node.js versions can run .ts files directly for development (type-stripping the syntax at runtime, without a full type-check), and tools like ts-node and tsx have long provided similar capability — useful for quick scripts and development, though a real build step (tsc) is still the standard for producing deployable JavaScript output.

Sources

Microsoft. TSConfig Reference, typescriptlang.org/tsconfig, and "What is a tsconfig.json", typescriptlang.org/docs/handbook/tsconfig-json.html.

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