Use TypeScript for web apps and APIs

Cost

Open source. Apache-2.0 licence, free to use in any project.

How to do it

TypeScript passes all five tests. Version 1.0 shipped in April 2014, and 7.0 shipped on 8 July 2026. The npm package had 184 million downloads in the week to 18 October 2026. In the Stack Overflow Developer Survey 2025, 43.6% of developers used it. It is Apache-2.0 licensed. Types let the compiler catch the mistakes an agent makes before a visitor sees them. Version 7.0 is a rewrite of the compiler in Go, so pin 6.0 until 7.0 has been out six months, on 8 January 2027. Choose something else when the team only knows Python, or the app is mostly data work, as the Python rule below says. Turn on every check, as Use TypeScript in strict mode says.

Examples

Using these examples: they show one way to follow this rule. Keep the behaviour and the check, not the syntax. Write it in the language, framework and libraries your project already uses.

JSON example

{
  "compilerOptions": {
    "strict": true,
    "target": "ES2022",
    "module": "NodeNext",
    "noEmit": true
  }
}

TypeScript example

type Booking = { id: string; startsAt: Date; seats: number };

export function totalSeats(bookings: Booking[]): number {
  return bookings.reduce((sum, booking) => sum + booking.seats, 0);
}

Shell example

npm install --save-dev typescript@6.0
npx tsc --noEmit

How to check

npx tsc --version prints 6.0 or 7.0. tsconfig.json sets "strict": true. npx tsc --noEmit exits with code 0 in continuous integration.

Sources

• TypeScript documentation
• TypeScript tsconfig reference

Related rules

• Use TypeScript in strict mode in Software choices