The TSConfig Cheat Sheet

tsconfig.json scares everyone. It's a huge file with a TON of potential options.

But really, there are only a few configuration options you need to care about. Let's figure them out, and cheatsheet them.

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Quickstart

Want just the code? Here you go:

{
  "compilerOptions": {
    /* Base Options: */
    "esModuleInterop": true,
    "skipLibCheck": true,
    "target": "es2022",
    "allowJs": true,
    "resolveJsonModule": true,
    "moduleDetection": "force",
    "isolatedModules": true,
    "verbatimModuleSyntax": true,

    /* Strictness */
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "noImplicitOverride": true,

    /* If transpiling with TypeScript: */
    "module": "NodeNext",
    "outDir": "dist",
    "sourceMap": true,

    /* AND if you're building for a library: */
    "declaration": true,

    /* AND if you're building for a library in a monorepo: */
    "composite": true,
    "declarationMap": true,

    /* If NOT transpiling with TypeScript: */
    "module": "preserve",
    "noEmit": true,

    /* If your code runs in the DOM: */
    "lib": ["es2022", "dom", "dom.iterable"],

    /* If your code doesn't run in the DOM: */
    "lib": ["es2022"]
  }
}

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Full Explanation

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Base Options

Here are the base options I recommend for all projects.

{
  "compilerOptions": {
    "esModuleInterop": true,
    "skipLibCheck": true,
    "target": "es2022",
    "allowJs": true,
    "resolveJsonModule": true,
    "moduleDetection": "force",
    "isolatedModules": true,
    "verbatimModuleSyntax": true
  }
}

• esModuleInterop: Helps mend a few of the fences between CommonJS and ES Modules.
• skipLibCheck: Skips checking the types of .d.ts files. This is important for performance, because otherwise all node_modules will be checked.
• target: The version of JavaScript you're targeting. I recommend es2022 over esnext for stability.
• allowJs and resolveJsonModule: Allows you to import .js and .json files. Always useful.
• moduleDetection: This option forces TypeScript to consider all files as modules. This helps to avoid 'cannot redeclare block-scoped variable' errors.
• isolatedModules: This option prevents a few TS features which are unsafe when treating modules as isolated files.
• verbatimModuleSyntax: This option forces you to use import type and export type, leading to more predictable behavior and fewer unnecessary imports. With module: NodeNext, it also enforces you're using the correct import syntax for ESM or CJS.

#

Strictness

Here are the strictness options I recommend for all projects.

{
  "compilerOptions": {
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "noImplicitOverride": true
  }
}

• strict: Enables all strict type checking options. Indispensable.
• noUncheckedIndexedAccess: Prevents you from accessing an array or object without first checking if it's defined. This is a great way to prevent runtime errors, and should really be included in strict.
• noImplicitOverride: Makes the override keyword actually useful in classes.

Many folks recommended the strictness options in tsconfig/bases, a wonderful repo which catalogs TSConfig options. These options include lots of rules which I consider too 'noisy', like noImplicitReturns, noUnusedLocals, noUnusedParameters, and noFallthroughCasesInSwitch. I recommend you add these rules to your tsconfig.json only if you want them.

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Transpiling with TypeScript

If you're transpiling your code (creating JavaScript files) with tsc, you'll want these options.

{
  "compilerOptions": {
    "module": "NodeNext",
    "outDir": "dist"
  }
}

• module: Tells TypeScript what module syntax to use. NodeNext is the best option for Node. moduleResolution: NodeNext is implied from this option.
• outDir: Tells TypeScript where to put the compiled JavaScript files. dist is my preferred convention, but it's up to you.

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Building for a Library

If you're building for a library, you'll want declaration: true.

{
  "compilerOptions": {
    "declaration": true
  }
}

• declaration: Tells TypeScript to emit .d.ts files. This is needed so that libraries can get autocomplete on the .js files you're creating.

#

Building for a Library in a Monorepo

If you're building for a library in a monorepo, you'll also want these options.

{
  "compilerOptions": {
    "declaration": true,
    "composite": true,
    "sourceMap": true,
    "declarationMap": true
  }
}

• composite: Tells TypeScript to emit .tsbuildinfo files. This tells TypeScript that your project is part of a monorepo, and also helps it to cache builds to run faster.
• sourceMap and declarationMap: Tells TypeScript to emit source maps and declaration maps. These are needed so that when consumers of your libraries are debugging, they can jump to the original source code using go-to-definition.

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Not Transpiling with TypeScript

If you're not transpiling your code with tsc, i.e. using TypeScript as more of a linter, you'll want these options.

{
  "compilerOptions": {
    "module": "preserve",
    "noEmit": true
  }
}

• module: preserve is the best option because it most closely mimics how bundlers treat modules. moduleResolution: Bundler is implied from this option.
• noEmit: Tells TypeScript not to emit any files. This is important when you're using a bundler so you don't emit useless .js files.

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Running in the DOM

If your code runs in the DOM, you'll want these options.

{
  "compilerOptions": {
    "lib": ["es2022", "dom", "dom.iterable"]
  }
}

• lib: Tells TypeScript what built-in types to include. es2022 is the best option for stability. dom and dom.iterable give you types for window, document etc.

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Not Running in the DOM

If your code doesn't run in the DOM, you'll want lib: ["es2022"].

{
  "compilerOptions": {
    "lib": ["es2022"]
  }
}

These are the same as above, but without the dom and dom.iterable typings.

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Changelog

I've been updating this cheatsheet as TypeScript evolves, and as I refine my view of what belongs in a reusable tsconfig.json. Here's the changelog:

• 2024-04-23: Added verbatimModuleSyntax to the base options. With the introduction of module: Preserve, verbatimModuleSyntax is much more useful. Many applications do 'fake ESM', where they write imports and exports but transpile to CommonJS. Next.js is a common example. Before module: Preserve, verbatimModuleSyntax would error on every single import or export statement because it was expecting a module. With module: Preserve, its scope is narrowed making sure import/export type is used correctly.
• 2024-04-23: Added noImplicitOverride to the strictness options. Never knew about this option, or the override keyword, until I discovered it while researching my book. noImplicitOverride is a very small improvement at no cost, so why not?

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What Did I Miss?

Hopefully, I've given you a bit of inspiration for the next time you need to configure TypeScript.

Did I miss anything? Let me know:

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