ts-node

Installation and Setup

A project installs ts-node as a dev dependency, together with the TypeScript compiler and the Node.js type definitions:

$ npm install --save-dev ts-node typescript@6 @types/node

ts-node reads its compiler settings from the project’s tsconfig.json file. The tsc --init command creates one with the current recommended options:

$ npx tsc --init

Created a new tsconfig.json

You can learn more at https://aka.ms/tsconfig

Next, confirm the installed version:

$ npx ts-node --version
v10.9.2

Key Features

• Type-checks each file before it runs and stops with a TSError when the check fails.
• Compiles TypeScript just in time, so a project doesn’t need a build step before it runs.
• Skips type checking with the --transpileOnly flag, or -T, for faster startup.
• Opens a TypeScript REPL when it runs without a file name.
• Hooks into the node command itself through node --require ts-node/register.

Usage

Say a shop’s cart.ts file declares an Item interface with numeric price and quantity fields, then logs the cart total. Running it through npx uses the project’s local copy of ts-node:

$ npx ts-node cart.ts
Total: 22.5

If one item’s price is the string "5" instead of a number, the type check fails and the file doesn’t run:

$ npx ts-node cart.ts
TSError: ⨯ Unable to compile TypeScript:
cart.ts(7,5): error TS2322: Type 'string' is not assignable to type 'number'.

The --transpileOnly flag skips the check and runs the same file anyway. JavaScript coerces "5" to a number during the multiplication, so the total doesn’t change:

$ npx ts-node --transpileOnly cart.ts
Total: 22.5

An npm script in package.json can call ts-node, so npm start runs the file:

{
  "scripts": {
    "start": "ts-node cart.ts"
  }
}

For every option and the ES module setup, see the ts-node documentation.