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3.2.26 • Public • Published


esrun is a "work out of the box" library to execute Typescript (as well as modern Javascript with decorators and stuff) without having to use a bundler. This is useful for quick demonstrations or when launching your tests written in Typescript.

This library is a thin wrapper around esbuild which compiles Typescript almost instantly.

The harder work to run typescript is to deal with dependencies. For example, you may need to import other Typescript files, but also libraries written in Javascript and using either the CJS or the ESM format. All these use cases should be considered.

esrun is able to handle all the annoying stuff and make things work as you would expect.


Global installation

Install the library globally with your favorite package manager:

npm i -g esrun

Then you can execute any Typescript file in the same way Node would execute a Javascript file:

esrun foo.ts

You can pass arguments like any process:

esrun foo.ts --option=bar --verbose -S

All file dependencies will be bundled and executed as well.

External module dependencies won't be bundled, it's up to the node engine to resolve dependencies.

Local installation

Install the library locally with your favorite package manager.

npm i -D esrun

Then you can use it in your package.json scripts:

   "scripts": {
      "test": "esrun test"

Running npm run test will run the first file that exists in the following list:

  • /test.ts
  • /test/index.ts
  • /test/test.ts
  • /test/main.ts
  • /test.js
  • /test/index.js
  • /test/test.js
  • /test/main.js

CLI parameters syntax

There are two kinds of parameters that you can pass to the esrun cli:

  1. esrun parameters, that will impact how to execute your Typescript file,
  2. and program parameters, that will be passed into process.argv to the file you want to execute.

esrun parameters follow the same syntax convention as node, ie:

  • it must start with a double hyphen "--"
  • then be followed by the name of the parameter
  • then, if a value is necessary, use an equal symbol "=" followed by the value, without space.


esrun --tsconfig=/path/to/tsconfig.json myFileToExecute.ts

All parameters that come after the file to execute are program parameters and will be sent via process.argv.

In this example, "foo" and "bar" will be sent to myFileToExecute:

esrun myFileToExecute.ts foo bar

Custom tsconfig.json

You can pass a custom path to your tsconfig.json file from the CLI:

esrun --tsconfig=/custom/path/to/tsconfig.json foo.ts

Top-level await

Esrun is compatible with top-level await.

To enable top-level await, you need to set the option "module": "esnext" in your tsconfig.json.

Watch mode

You can also execute esrun in watch mode.

In watch mode, your file will automatically be re-executed every time itself or one of its dependencies is updated.

esrun --watch foo.ts

The --watch (or -w) option must be placed before the path of the file to execute. If you place it after the file path, it will be passed as an argument to foo.ts instead.

This feature is very useful when you are doing test-driven development. You can just run esrun --watch test.ts and enjoy a live output of your changes right into your console.

You may want to watch other files than your code files. For example, if you load data from a configuration file. In this case you can specify a glob (or a list of globs) that have to be watched:

esrun --watch=src/*.json foo.ts

Then any json file in the src/folder will re-trigger the run.

You can use several globs separated by a comma (but no space):

esrun --watch=src/*.json,test/*.json foo.ts

Preventing console clearing

In watch mode, every file change will trigger a console clearing. You can disable this behavior with the --preserveConsole option:

esrun --watch --preserveConsole foo.ts

Inspect mode

You can also execute esrun in inspect mode.

When run in inspect mode, your code will be connected to the Webkit DevTools to benefit the power of the browser console instead of the terminal console.

First, run your program in inspect mode:

esrun --inspect foo.ts

Then open about:inspect in a Chrome / Brave / Edge browser. You should see your program running in the Remote targets section.

Click on Open dedicated DevTools for Node and enjoy the browser console for your back-end program.

In case of troubleshooting, read the node documentation.

Inspect and watch mode are alas not compatible yet.

Sudo mode

You can run the script in sudo mode:

esrun --sudo myScript.ts

Other node cli options

esrun uses esbuild to transform Typescript to Javascript, and then Node to execute it.

You can pass custom options to the node cli by prefixing the option name with "--node", like this:

esrun --node-max-old-space-size=4096 foo.ts
esrun --node-no-warnings foo.ts

Importing a CJS module

If you import a CJS module (like the typescript library itself), it's likely that you will need to set the esModuleInterop flag in your tsconfig.json file:

	"compilerOptions": {
		"esModuleInterop": true

This will suppress the import errors from the Typescript compiler and allow you to write import ts from "typescript" instead of import * as ts from "typescript" - the latest syntax being not standard ESM.

Using a directory as an entry point

If the given entry point is a directory, the following actions will be executed in order to find the right entry file:

  • check if a package.json file exists with a main field. The entry file will be the value of the main field, relative to the package.json directory.
  • check if an index.ts file exists in the given directory.
  • check if an eponym file exists in the given directory.
  • check if an eponym file with the .ts extension exists in the given directory.
  • check if a main.ts file exists in the given directory.
  • check if a index.js file exists in the given directory.
  • check if an eponym file with the .js extension exists in the given directory.
  • check if a main.js file exists in the given directory.


The library exports a single function that you can use to programmatically execute a Typescript file.

import esrun from 'esrun'

export async function esrun(filePath: string, options?: Options): Promise<void>

export type Options = {
   // arguments to pass to the script
   args?: string[] = []

   // if true, will reload the script on file changes
   // you can also pass an additional array of globs to watch
   watch?: boolean | string[] = false

   // if true, prevent console clearing on watch mode
   preserveConsole?: boolean

   // if true, turn on inspect mode to use browser's console
   inspect?: boolean = false

   // if false, do not transform __dirname and __filename
   // (the CLI option to disable file constants is --noFileConstants)
   fileConstants?: boolean = true

   // if false, external packages will be bundled
   makeAllPackagesExternal?: boolean = true

   // if false, process.exit() won't be called after execution
   exitAfterExecution?: boolean = true

   // enable use of process.send() from the children
   interProcessCommunication?: boolean = false

   // additional options to pass to node's cli
   nodeOptions?: Record<string, Parameter> = {}

   // indicate the mode to use to run code
   // "cliParameters" means the code is passed to the node program
   // as parameters
   // "temporaryFile" means a temporary file is created inside
   // the node_modules folder, then executed, then deleted
   sendCodeMode?: "cliParameters" | "temporaryFile"

   // executed before the code is executed (after the build)
   beforeRun?: () => unknown

   // executed after the code is executed
   afterRun?: () => unknown

Create a new runner to get / transform generated code

To have full control, you can create your own script runner instance:

import { Runner } from 'esrun'

const runner = new Runner(inputFile: string, options?: Options)

// build the given file and all its dependencies
await BuildOptions)

// you can see what the generated code is
console.log("Generated javascript code:", runner.outputCode)

// you can apply transformations to the code
await runner.transform(code => `console.log('Hello world!');\n` + code)

// then execute the build and return the given status
const status = await runner.execute()

Receive data

You can receive data from a script you executed by turning on the option interProcessCommunication.

When the option is on, the script will be able to call process.send(message: string).

At the end of the execution, the sent messages will be disponible through runner.output.

Let's suppose you have the following file helloWorld.ts:

// helloWorld.ts
process.send('Hello world')

Then you can receive data fro this script this way:

const runner = new Runner('helloWorld.ts', { interProcessCommunication: true })

await runner.execute({ exitAfterExecution: false })

console.log("Received data:", runner.output)
// should log 'Received data: Hello world'


The changelog is available here.

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