JS with Types Start

Tool

jsconfig.json generator

Choose your project shape and how strict the checker should be. The config, the npm scripts and the install line update as you go, ready to copy.

Each shape matches a setup page in the quick start. Options that do not apply to a shape are hidden for it, such as Node.js types for the browser.

How strict
Options

jsconfig.json 

{
  "compilerOptions": {
    "checkJs": true,
    "noEmit": true,
    "strict": true,
    "module": "nodenext",
    "moduleResolution": "nodenext",
    "target": "es2024",
    "types": ["node"],
    "skipLibCheck": true
  },
  "include": ["src/**/*.js", "test/**/*.js"]
}

Save it next to package.json.

package.json 

{
  "type": "module",
  "scripts": {
    "lint": "tsc -p jsconfig.json",
    "lint:watch": "tsc -p jsconfig.json --watch --preserveWatchOutput"
  }
}

Merge these keys into your package.json.

Install 

npm install --save-dev typescript @types/node

Development dependencies only: nothing here ships with your code.

The same options with tsc --init 

npx tsc --init --checkJs --noEmit --strict --module nodenext --moduleResolution nodenext --target es2024 --types node --skipLibCheck --sourceMap false --declaration false --declarationMap false --noUncheckedIndexedAccess false --exactOptionalPropertyTypes false --verbatimModuleSyntax false --isolatedModules false --noUncheckedSideEffectImports false --moduleDetection auto

Writes tsconfig.json with exactly these compiler options (and "jsx", which does nothing without JSX). Rename it to jsconfig.json and add the include list by hand.

How it works

The generator starts from the checked config on the project shape's quick-start page, for example the Node.js ES modules setup, then applies the strictness level and the options you pick. It works from the choices on this page and does not read your files.

Every combination it can produce is parsed by TypeScript 5.9 in this site's tests, and its tsc --init line is run through TypeScript's own init code to confirm it writes the same compiler options.

The three levels

  • Relaxed. Checks what TypeScript can infer; untyped parameters stay allowed. A first step for an existing codebase.
  • Recommended. strict on: a parameter TypeScript cannot infer needs a type, and null and undefined are checked. The setting for new code.
  • Strict. strict plus checked index access, exact optional properties, and no missing returns or switch fall-through.

Not sure? Start with recommended on new code. On an existing codebase, start relaxed, fix what it finds, then move up; checkJs explains the order.

  • Quick start

    Node.js with ES modules

    Type-check a Node.js project written as ES modules: the jsconfig.json, @types/node, the npm scripts and the import rules that nodenext enforces.

  • jsconfig.json option

    checkJs

    checkJs turns on TypeScript's error reporting for .js files. What it checks, how it relates to allowJs and // @ts-check, and how to switch it on.

  • jsconfig.json option

    strict

    strict turns on the strict type-checking family with one switch: nine options in TypeScript 5.9. What each catches in a .js file, and how to turn one back off.

  • jsconfig.json option

    skipLibCheck

    skipLibCheck skips checking every .d.ts file, your own included. A jsconfig.json turns it on by default, which can hide a typo in a .d.ts you wrote.

  • jsconfig.json option

    resolveJsonModule

    resolveJsonModule lets you import .json files and types their contents. nodenext and bundler turn it on; ES modules still need the json import attribute.

  • Editor setup

    VS Code

    Set up VS Code for type-checked JavaScript: how it reads jsconfig.json, using the project's TypeScript version, and listing errors in files you have not opened.