checkdigit/typescript-config

Copyright © 2021–2026 Check Digit, LLC

Introduction

This module contains the standard Check Digit TypeScript configuration, along with our standard build tool builder.

TypeScript Configuration

• currently supports Node 24.18.0 up to, but not including, Node 25, or Node 26 and above.
• Node 25 is intentionally not part of the support contract.
• emits esnext, with the default libraries, to avoid down-leveling. It is intended that application spec tests pick up any issues with using newer features unavailable in a particular environment. Browsers and Node.js are fast-moving targets, and can add language features at any time.
• uses the module type of esnext.
• all compiler options set for maximum strictness.

Builder

builder is a command line tool that generates ESM modules from the TypeScript source. It is intended to be used when publishing a package to NPM, or to bundle a package for deployment. It uses tsc for generating types, and esbuild for generating code.

Note: the require function will be defined as a global variable, to allow dynamic requires by CommonJS submodules. This is not a problem for Node.js, but will cause issues in a browser environment.

Options

• --type the type of output to generate. Defaults to module (ESM). Valid values are module or types.
• --entryPoint the entry point for the bundle, relative to the inDir. if not provided, the files in the inDir will be processed as individual unbundled files.
• --inDir the input source code directory.
• --outDir the output directory.
• --outFile the output file, relative to --outDir. This is provided for single-file bundles, along with --entryPoint.
• --external external modules to exclude from the bundle. Built-in node modules are automatically excluded. A wildcard * can be used to exclude multiple external modules.
• --minify whether to minify the output.
• --sourceMap whether to include inline sourcemap.

Examples

# build ESM .mjs files from TypeScript source
npx builder --type=module --outDir=build-esm

# build single-file ESM .mjs bundle from TypeScript source
npx builder --type=module --outDir=build-esm-bundle --entryPoint=index.ts --outFile=index.mjs

Tests

This module includes a number of integration-style tests, to ensure that a specific version of TypeScript will interoperate with builder, in addition to runtimes, libraries and frameworks used by Check Digit:

• Recent TC39 proposals
• Node versions supported by AWS Lambda, Google Cloud Functions, and Azure Functions
• ESLint and @typescript-eslint/eslint-plugin
• Built-in node:test runner
• prettier
• tsc, and specific features introduced in each version of TypeScript
• esbuild
• Wallaby.js (supports node:test by relying on native Node type-stripping support)

We do this to ensure that TypeScript upgrades do not break these dependencies, and that updates to these related projects do not break builds.

Note: New major versions of TypeScript are not immediately supported by projects such as eslint, prettier, typescript-eslint, etc. Our policy is to wait until these projects fully support the new version of TypeScript, and/or without emitting warnings during these tests, before publishing.

A note about versioning

Strict semver is a little complicated, as TypeScript itself does not adhere to semver. So our "best effort" policy is:

• Each update to the minimum Node target (e.g., Node 18 to Node 20), or a change to a major compiler output option (e.g. module, target or moduleResolution) will result in a new major version of this module. We coordinate this with whatever the latest LTS version of Node is currently supported by Amazon Lambda, Google Cloud Functions, and Azure Functions.
• Each new "major" version of TypeScript (e.g. 5.7.x to 5.8.x) will result in a new minor version of this module.
• A new minor update of TypeScript (e.g. 5.7.2 to 5.7.3) or a key dependency (e.g., Node 22.11 to Node 22.14) may result in a patch.

Bear in mind, any update of TypeScript can potentially break your build. But hopefully in a way that's useful.

Installation

npm add -D @checkdigit/typescript-config

Note: you do not need to explicitly install TypeScript itself, as the most recent supported version comes in as a peer dependency of @checkdigit/typescript-config.

Make sure your project's tsconfig.json extends @checkdigit/typescript-config.

Example tsconfig.json

{
  "extends": "@checkdigit/typescript-config"
}

Note this configuration has moduleResolution set to bundler. This requires the use of the builder command to produce working code for deployment.

License

MIT