ts-run

The minimalist TypeScript script runner for NodeJS.

Features

• On-demand TypeScript transpilation so fast you won't even notice.
• Supports source maps for accurate stack traces.
• Does not spawn another process to transpile TypeScript.
• Does not spawn another Node process to run your script.
• Strictly follows modern Node semantics for ESM / CommonJS modules.
• Zero config: no config file, no command line arguments, no environment variables, no nothing.
• Does not even need a tsconfig.json (though you may need one for authoring your scripts -- keep reading below).
• Light: only 220 kilobytes installed!
• Zero dependency!

Non-features

• Not for running full-blown TypeScript projects.
• No REPL support.

About

ts-run is a CLI command that you can use to run TypeScript scripts in NodeJS as if they were written in plain JavaScript. It is a simple as:

ts-run ./some-script.ts

The idea is that you take advantage of your IntelliSense-compatible editor to author your scripts with full type checking on, and ts-run will transparently run them without you having to run the TypeScript compliler beforehand.

Installation and usage

ts-run requires a modern (as of january 2024) version of NodeJS:

• Node 18 version 18.19.0 or later
• Node 20 version 20.6.0 or later
• Any version >= 21

Global install

For everyday use, you may want to install ts-run globally:

npm install -g @septh/ts-run

and have it always available in your CLI:

ts-run path/to/some/script.ts

Local install

Or you may install it locally in a project:

npm install --save-dev @septh/ts-run

and then call it from the scripts section in package.json:

{
    "scripts": {
        "get-data": "ts-run ./scripts/download-data.ts",
        "release": "ts-run ./scripts/prepare-release.ts"
    }
}

or from the command line:

npx ts-run ./scripts/do-something.ts

TypeScript to JavaScript considerations

ts-run's sole role is to transpile TypeScript code to JavaScript code, no more, no less. It does not try to optimize or minify your code and it does not downlevel nor polyfill JavaScript. Therefore, there are a few things you should keep in mind while authoring your scripts.

import specifiers

Use the .ts, .mts or .cts extensions when importing modules. Extensions are mandatory in ESM scripts and highly recommended in CJS scripts.

import { something } from './utilities.ts'

Contrary to the TypeScript compiler, ts-run will not try and find a corresponding .ts file if you use a .js specifier. See the authoring section for details on how to enable .ts extension imports in your editor.

import vs require

ts-run strictly follows the NodeJS semantics about ES and CommonJS modules. Refer to the following table to decide whether you should use import or require:

	ES importer	CJS importer
ES importee	import ... from 'specifier' or const ... = await import('specifier')	const ... = await import('specifier')
CJS importee	import namespace = require('specifier') or const ... = await import('specifier')	import ... from 'specifier' or const ... = require('specifier')

Notes:

1. The import ... from 'specifier' syntax is left as is in ES modules and transformed to const ... = require('specifier') in CommonJS modules.
2. The import namespace = require('specifier') syntax is valid in ES modules only and is transformed to const require = createRequire(); const namespace = require('specifier'), with the createRequire() call being hoisted if used several times.
3. Dynamics imports are always left untouched.

Type-only imports and exports

I find it generally better to be explicit about type-only imports and exports by using TypeScript's import type ..., import { type ... } and export type ... syntax.

However, because not everyone is willing to type the extra characters, ts-run version 1.2.3 and later will transparently ignore type-only imports and exports.

Path substitutions

TypeScript's module resolution specificities are not handled; instead, Node's module resolution algorithm is always used. In other words, as far as ts-run is concerned, it is like if moduleResolution was always set to Node16 and paths was not set.

Sucrase

ts-run uses a stripped down build of Sucrase under the hood and therefore exhibits the same potential bugs and misbehaviors than Sucrase.

If ts-run seems to not work as you'd expect, you should first check if this there is a Sucrase issue open for your problem. If not, please file an issue on ts-run.

Authoring your scripts

As stated earlier, ts-run does not need (and in fact, does not even look for) a tsconfig.json file. The same is not true however for the TypeScript Language Server that your IntelliSense-aware editor relies on. You'll find the following tsconfig.json useful to get the right warnings and errors reports in your IDE:

{
  "compilerOptions": {
    // This tells the TypeScript language server that this directory contains Node scripts.
    "module": "Node16",

    // - Scripts must import .ts files as ts-run does not map .js to .ts
    // - `noEmit` is required when using `allowImportingTsExtensions`
    "allowImportingTsExtensions": true,
    "noEmit": true,

    // Scripts are transpiled in isolation; this imposes a few restrictions
    // on some TypeScript features like const enums or namespaces.
    // (see https://www.typescriptlang.org/tsconfig#isolatedModules)
    "isolatedModules": true,

    // Of course, add any other type-checking options you deem necessary:
    "strict": true
    // etc.
  }
}

For reference, you can find such a tsconfig.json file in the test folder of this repository.

Using with a test-runner

I have tested ts-run with ava and Node itself and it works very well in both cases. I can see no reason why it wouldn't work with another test-runner.

With node:test

This very repo is using Node as its test-runner of choice -- see the scripts section in package.json:

  "scripts": {
    "test": "ts-run test/check-node-21.ts && node --import=@septh/ts-run/register --test test/**/*.test.{ts,mts,cts}"
  }

Note: to pass command line options to Node itself, you need to use the --import syntax as shown above.

The only caveat here is that Node started to support glob patterns as arguments to the --test option only since version 21, hence the little script that checks the version of Node before running the tests. This is a limitation of Node, not ts-run.

On the other hand, this works with older versions of Node supported by ts-run:

  "scripts": {
    "test": "node --import=@septh/ts-run/register --test my-test-script.ts"
}

With ava

Add the following entry to your package.json:

  "ava": {
    "extensions": {
      "ts": "module",
      "mts": "module",
      "cts": "commonjs"
    },
    "nodeArguments": [
      "--import=@septh/ts-run/register"
    ]
  }

Here's an example: https://github.com/Septh/rollup-plugin-node-externals

With other test-runners

Any test-runner that provides a mean to specify Node arguments (just like ava above) should work happily with ts-run.

In the worst case, you can always use the NODE_OPTIONS environment variable:

NODE_OPTIONS="--import=@septh/ts-run/register" my-test-runner

Debugging scripts with VS Code

Because ts-run generates sourcemaps, you can set breakpoints in your script, inspect variables, etc.

Either run ts-run in the VS Code Javascript Debug Terminal or use the following launch.json configuration (replace <path-to-your-script.ts> with the actual path to your script):

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Run with ts-run",
            "request": "launch",
            "type": "node",
            "runtimeArgs": [
                "--import=@septh/ts-run/register"
            ],
            "program": "${workspaceFolder}/<path-to-your-script.ts>",
            "windows": {
                "program": "${workspaceFolder}\\<path-to-your-script.ts>"
            },
            "skipFiles": [
                "<node_internals>/**",
                "**/node_modules/**"
            ],
            "resolveSourceMapLocations": [
                "!**/node_modules/**"
            ],
        }
    ]
}

Licence

MIT.