Shared TypeScript configuration for fastify projects

$ npm i -D fastify-tsconfig

Create your own tsconfig.json in the projects' root folder and extend it from fastify-tsconfig, overriding or adding the desired settings. By default, no outDir is set (because of this issue), so be sure to add one.

This configuration sets "module" and "moduleResolution" to NodeNext. This means that TypeScript will read the nearest package.json file in the scope and search for the "type" field or the absence of it.

If type is not set or is "type": "commonjs" the emitted code will be CommonJS, with .js extension. Moreover, tsc will complain if ESM-only properties/features are used in source files. If you want to emit .mjs files, use the .mts extension. On the other hand, if "type": "module" is set, the sources will be compiled to the ESM with the .js extension. In this case, if you want to emit .cjs files, use the .cts extension for the source file.

The "following the Node.js rules" goes also for the package.json exports field. If type is set, regardless of the value, TypeScript will check the exports field to know where the compiled code and the types are located. If the type field is not set, it will check for the main and types fields.

package.json

{
  "name": "my-package",
  "type": "commonjs",
  "main": "dist/index.js", // this is for older Node.js versions
  "types": "dist/index.d.ts", // this is optional and can be omitted
  "exports": {
    "import": "./dist/index.js",
    "require": "./dist/index.js",
    "types": "./dist/index.d.ts" // this is optional and can be omitted
 }
}

tsconfig.json

{
 "extends": "fastify-tsconfig",
 "compilerOptions": {
    "outDir": "dist",
    "sourceMap": true
  },
  "include": [
    "src/**/*.ts"
  ]
}

package.json

{
  "name": "my-package",
  "type": "module",
  "main": "dist/index.js", // this is for older Node.js versions
  "types": "dist/index.d.ts", // this is optional and can be omitted
  "exports": {
    "import": "./dist/index.js",
    "require": "./dist/index.js",
    "types": "./dist/index.d.ts" // this is optional and can be omitted
 }
}

tsconfig.json

{
 "extends": "fastify-tsconfig",
 "compilerOptions": {
    "outDir": "dist",
    "sourceMap": true
  },
  "include": [
    "src/**/*.ts"
  ]
}

Depending on the type of the project, you should add the following settings.

tsconfig.json

{
 "extends": "fastify-tsconfig",
 "compilerOptions": {
    "outDir": "dist",
    "sourceMap": true
 },
 "include": [
    "src/**/*.ts"
 ]
}

tsconfig.json

{
 "extends": "fastify-tsconfig",
 "compilerOptions": {
    "outDir": "dist",
    "declaration": true
 },
 "include": [
    "src/**/*.ts"
 ]
}

tsconfig.json

{
 "extends": "fastify-tsconfig",
 "compilerOptions": {
    "outDir": "dist",
    "declarationMap": true,
    "composite": true
 },
 "include": [
    "src/**/*.ts"
 ]
}

Check the other settings here

The configuration targets ES2023, which is supported in Node.js 20 and later. However, using ES2023 as a target makes widely used features not being compiled. To target an older version, override the target property.

Licensed under MIT.

Inspired by: sindresorhus/tsconfig