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Oct 11, 2021

TypeScript Node

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TypeScript execution and REPL for node.js, with source map and native ESM support.

The latest documentation can also be found on our website: https://typestrong.org/ts-node

Table of Contents

Overview

ts-node is a TypeScript execution engine and REPL for Node.js.

It JIT transforms TypeScript into JavaScript, enabling you to directly execute TypeScript on Node.js without precompiling. This is accomplished by hooking node's module loading APIs, enabling it to be used seamlessly alongside other Node.js tools and libraries.

Features

  • Automatic sourcemaps in stack traces
  • Automatic tsconfig.json parsing
  • Automatic defaults to match your node version
  • Typechecking (optional)
  • REPL
  • Write standalone scripts
  • Native ESM loader
  • Use third-party transpilers
  • Use custom transformers
  • Integrate with test runners, debuggers, and CLI tools
  • Compatible with pre-compilation for production

TypeScript REPL

Installation

# Locally in your project.
npm install -D typescript
npm install -D ts-node

# Or globally with TypeScript.
npm install -g typescript
npm install -g ts-node

# Depending on configuration, you may also need these
npm install -D tslib @types/node

Tip: Installing modules locally allows you to control and share the versions through package.json. TS Node will always resolve the compiler from cwd before checking relative to its own installation.

Usage

Shell

# Execute a script as `node` + `tsc`.
ts-node script.ts

# Starts a TypeScript REPL.
ts-node

# Execute code with TypeScript.
ts-node -e 'console.log("Hello, world!")'

# Execute, and print, code with TypeScript.
ts-node -p -e '"Hello, world!"'

# Pipe scripts to execute with TypeScript.
echo 'console.log("Hello, world!")' | ts-node

# Equivalent to ts-node --transpile-only
ts-node-transpile-only script.ts

# Equivalent to ts-node --cwd-mode
ts-node-cwd script.ts

Shebang

#!/usr/bin/env ts-node

console.log("Hello, world!")

Passing CLI arguments via shebang is allowed on Mac but not Linux. For example, the following will fail on Linux:

#!/usr/bin/env ts-node --files
// This shebang is not portable.  It only works on Mac

Instead, specify all ts-node options in your tsconfig.json.

Programmatic

You can require ts-node and register the loader for future requires by using require('ts-node').register({ /* options */ }). You can also use file shortcuts - node -r ts-node/register or node -r ts-node/register/transpile-only - depending on your preferences.

Note: If you need to use advanced node.js CLI arguments (e.g. --inspect), use them with node -r ts-node/register instead of ts-node's CLI.

Developers

ts-node exports a create() function that can be used to initialize a TypeScript compiler that isn't registered to require.extensions, and it uses the same code as register.

Configuration

ts-node supports a variety of options which can be specified via tsconfig.json, as CLI flags, as environment variables, or programmatically.

For a complete list, see Options.

CLI flags

ts-node CLI flags must come before the entrypoint script. For example:

$ ts-node --project tsconfig-dev.json say-hello.ts Ronald
Hello, Ronald!

Via tsconfig.json (recommended)

ts-node automatically finds and loads tsconfig.json. Most ts-node options can be specified in a "ts-node" object using their programmatic, camelCase names. We recommend this because it works even when you cannot pass CLI flags, such as node --require ts-node/register and when using shebangs.

Use --skip-project to skip loading the tsconfig.json. Use --project to explicitly specify the path to a tsconfig.json.

When searching, it is resolved using the same search behavior as tsc. By default, this search is performed relative to the entrypoint script. In --cwd-mode or if no entrypoint is specified -- for example when using the REPL -- the search is performed relative to --cwd / process.cwd().

You can use this sample configuration as a starting point:

{
  // This is an alias to @tsconfig/node12: https://github.com/tsconfig/bases
  "extends": "ts-node/node12/tsconfig.json",

  // Most ts-node options can be specified here using their programmatic names.
  "ts-node": {
    // It is faster to skip typechecking.
    // Remove if you want ts-node to do typechecking.
    "transpileOnly": true,

    "files": true,

    "compilerOptions": {
      // compilerOptions specified here will override those declared below,
      // but *only* in ts-node.  Useful if you want ts-node and tsc to use
      // different options with a single tsconfig.json.
    }
  },
  "compilerOptions": {
    // typescript options here
  }
}

Our bundled JSON schema lists all compatible options.

@tsconfig/bases

@tsconfig/bases maintains recommended configurations for several node versions. As a convenience, these are bundled with ts-node.

{
  "extends": "ts-node/node16/tsconfig.json",

  // Or install directly with `npm i -D @tsconfig/node16`
  "extends": "@tsconfig/node16/tsconfig.json",
}

Default config

If no tsconfig.json is loaded from disk, ts-node will use the newest recommended defaults from @tsconfig/bases compatible with your node and typescript versions. With the latest node and typescript, this is @tsconfig/node16.

Older versions of typescript are incompatible with @tsconfig/node16. In those cases we will use an older default configuration.

When in doubt, ts-node --show-config will log the configuration being used, and ts-node -vv will log node and typescript versions.

node flags

node flags must be passed directly to node; they cannot be passed to the ts-node binary nor can they be specified in tsconfig.json

We recommend using the NODE_OPTIONS environment variable to pass options to node.

NODE_OPTIONS='--trace-deprecation --abort-on-uncaught-exception' ts-node ./index.ts

Alternatively, you can invoke node directly and install ts-node via --require/-r

node --trace-deprecation --abort-on-uncaught-exception -r ts-node/register ./index.ts

Options

ts-node supports --print (-p), --eval (-e), --require (-r) and --interactive (-i) similar to the node.js CLI options.

Environment variables, where available, are in ALL_CAPS

Shell

  • -h, --help Prints the help text
  • -v, --version Prints the version. -vv prints node and typescript compiler versions, too
  • -e, --eval Evaluate code
  • -p, --print Print result of --eval
  • -i, --interactive Opens the REPL even if stdin does not appear to be a terminal

TSConfig

  • -P, --project [path] Path to TypeScript JSON project file
    Environment: TS_NODE_PROJECT
  • --skip-project Skip project config resolution and loading
    Default: false
    Environment: TS_NODE_SKIP_PROJECT
  • -c, --cwd-mode Resolve config relative to the current directory instead of the directory of the entrypoint script
  • -O, --compiler-options [opts] JSON object to merge with compiler options
    Environment: TS_NODE_COMPILER_OPTIONS
  • --show-config Print resolved tsconfig.json, including ts-node options, and exit

Typechecking

  • -T, --transpile-only Use TypeScript's faster transpileModule
    Default: false
    Environment: TS_NODE_TRANSPILE_ONLY
  • --type-check Opposite of --transpile-only
    Default: true
    Environment: TS_NODE_TYPE_CHECK
  • -H, --compiler-host Use TypeScript's compiler host API
    Default: false
    Environment: TS_NODE_COMPILER_HOST
  • --files Load files, include and exclude from tsconfig.json on startup
    Default: false
    Environment: TS_NODE_FILES
  • -D, --ignore-diagnostics [code] Ignore TypeScript warnings by diagnostic code
    Environment: TS_NODE_IGNORE_DIAGNOSTICS

Transpilation

  • -I, --ignore [pattern] Override the path patterns to skip compilation
    Default: /node_modules/
    Environment: TS_NODE_IGNORE
  • --skip-ignore Skip ignore checks
    Default: false
    Environment: TS_NODE_SKIP_IGNORE
  • -C, --compiler [name] Specify a custom TypeScript compiler
    Default: typescript
    Environment: TS_NODE_COMPILER
  • --transpiler [name] Specify a third-party, non-typechecking transpiler
  • --prefer-ts-exts Re-order file extensions so that TypeScript imports are preferred
    Default: false
    Environment: TS_NODE_PREFER_TS_EXTS

Diagnostics

  • --log-error Logs TypeScript errors to stderr instead of throwing exceptions
    Default: false
    Environment: TS_NODE_LOG_ERROR
  • --pretty Use pretty diagnostic formatter
    Default: false
    Environment: TS_NODE_PRETTY
  • TS_NODE_DEBUG Enable debug logging

Advanced

  • -r, --require [path] Require a node module before execution
  • --cwd Behave as if invoked in this working directory
    Default: process.cwd()
    Environment: TS_NODE_CWD
  • --emit Emit output files into .ts-node directory
    Default: false
    Environment: TS_NODE_EMIT
  • --scope Scope compiler to files within scopeDir. Anything outside this directory is ignored.
    *Default: false
    Environment: TS_NODE_SCOPE
  • --scopeDir Directory within which compiler is limited when scope is enabled.
    Default: First of: tsconfig.json "rootDir" if specified, directory containing tsconfig.json, or cwd if no tsconfig.json is loaded.
    Environment: TS_NODE_SCOPE_DIR
  • moduleType Override the module type of certain files, ignoring the package.json "type" field. See Module type overrides for details.
    Default: obeys package.json "type" and tsconfig.json "module"
    Can only be specified via tsconfig.json or API.
  • TS_NODE_HISTORY Path to history file for REPL
    Default: ~/.ts_node_repl_history
  • --no-experimental-repl-await Disable top-level await in REPL. Equivalent to node's --no-experimental-repl-await
    Default: Enabled if TypeScript version is 3.8 or higher and target is ES2018 or higher.
    Environment: TS_NODE_EXPERIMENTAL_REPL_AWAIT set false to disable

API

The API includes additional options not shown here.

CommonJS vs native ECMAScript modules

TypeScript is almost always written using modern import syntax, but it is also transformed before being executed by the underlying runtime. You can choose to either transform to CommonJS or to preserve the native import syntax, using node's native ESM support. Configuration is different for each.

Here is a brief comparison of the two.

CommonJS Native ECMAScript modules
Write native import syntax Write native import syntax
Transforms import into require() Does not transform import
Node executes scripts using the classic CommonJS loader Node executes scripts using the new ESM loader
Use any of:
ts-node CLI
node -r ts-node/register
NODE_OPTIONS="ts-node/register" node
require('ts-node').register({/* options */})
Must use the ESM loader via:
node --loader ts-node/esm
NODE_OPTIONS="--loader ts-node/esm" node

CommonJS

Transforming to CommonJS is typically simpler and more widely supported because it is older. You must remove "type": "module" from package.json and set "module": "CommonJS" in tsconfig.json.

{
  // This can be omitted; commonjs is the default
  "type": "commonjs"
}
{
  "compilerOptions": {
    "module": "CommonJS"
  }
}

If you must keep "module": "ESNext" for tsc, webpack, or another build tool, you can set an override for ts-node.

{
  "compilerOptions": {
    "module": "ESNext"
  },
  "ts-node": {
    "compilerOptions": {
      "module": "CommonJS"
    }
  }
}

Native ECMAScript modules

Node's ESM loader hooks are experimental and subject to change. ts-node's ESM support is as stable as possible, but it relies on APIs which node can and will break in new versions of node. Thus it is not recommended for production.

For complete usage, limitations, and to provide feedback, see #1007.

You must set "type": "module" in package.json and "module": "ESNext" in tsconfig.json.

{
  "type": "module"
}
{
  "compilerOptions": {
    "module": "ESNext" // or ES2015, ES2020
  }
}

Troubleshooting

Understanding configuration

ts-node uses sensible default configurations to reduce boilerplate while still respecting tsconfig.json if you have one. If you are unsure which configuration is used, you can log it with ts-node --show-config. This is similar to tsc --showConfig but includes "ts-node" options as well.

ts-node also respects your locally-installed typescript version, but global installations fallback to the globally-installed typescript. If you are unsure which versions are used, ts-node -vv will log them.

$ ts-node -vv
ts-node v10.0.0
node v16.1.0
compiler v4.2.2

$ ts-node --show-config
{
  "compilerOptions": {
    "target": "es6",
    "lib": [
      "es6",
      "dom"
    ],
    "rootDir": "./src",
    "outDir": "./.ts-node",
    "module": "commonjs",
    "moduleResolution": "node",
    "strict": true,
    "declaration": false,
    "sourceMap": true,
    "inlineSources": true,
    "types": [
      "node"
    ],
    "stripInternal": true,
    "incremental": true,
    "skipLibCheck": true,
    "importsNotUsedAsValues": "error",
    "inlineSourceMap": false,
    "noEmit": false
  },
  "ts-node": {
    "cwd": "/d/project",
    "projectSearchDir": "/d/project",
    "require": [],
    "project": "/d/project/tsconfig.json"
  }
}

Understanding Errors

It is important to differentiate between errors from ts-node, errors from the TypeScript compiler, and errors from node. It is also important to understand when errors are caused by a type error in your code, a bug in your code, or a flaw in your configuration.

TSError

Type errors from the compiler are thrown as a TSError. These are the same as errors you get from tsc.

SyntaxError

Any error that is not a TSError is from node.js (e.g. SyntaxError), and cannot be fixed by TypeScript or ts-node. These are bugs in your code or configuration.

Unsupported JavaScript syntax

Your version of node may not support all JavaScript syntax supported by TypeScript. The compiler must transform this syntax via "downleveling," which is controlled by the tsconfig "target" option. Otherwise your code will compile fine, but node will throw a SyntaxError.

For example, node 12 does not understand the ?. optional chaining operator. If you use "target": "esnext", then the following TypeScript syntax:

const bar: string | undefined = foo?.bar;

will compile into this JavaScript:

const a = foo?.bar;

When you try to run this code, node 12 will throw a SyntaxError. To fix this, you must switch to "target": "es2019" or lower so TypeScript transforms ?. into something node can understand.

Make it fast

These tricks will make ts-node faster.

Skip typechecking

It is often better to use tsc --noEmit to typecheck once before your tests run or as a lint step. In these cases, ts-node can skip typechecking.

With typechecking

  • Avoid dynamic require() which may trigger repeated typechecking; prefer import
  • Try with and without --files; one may be faster depending on your project
  • Check tsc --showConfig; make sure all executed files are included
  • Enable skipLibCheck
  • Set a types array to avoid loading unnecessary @types

Advanced

How It Works

ts-node works by registering hooks for .ts, .tsx, .js, and/or .jsx extensions.

Vanilla node loads .js by reading code from disk and executing it. Our hook runs in the middle, transforming code from TypeScript to JavaScript and passing the result to node for execution. This transformation will respect your tsconfig.json as if you had compiled via tsc.

.js and .jsx are only transformed when allowJs is enabled.

.tsx and .jsx are only transformed when jsx is enabled.

Warning: if a file is ignored or its file extension is not registered, node will either fail to resolve the file or will attempt to execute it as JavaScript without any transformation. This may cause syntax errors or other failures, because node does not understand TypeScript type syntax nor bleeding-edge ECMAScript features.

Warning: When ts-node is used with allowJs, all non-ignored JavaScript files are transformed using the TypeScript compiler.

Skipping node_modules

By default, TypeScript Node avoids compiling files in /node_modules/ for three reasons:

  1. Modules should always be published in a format node.js can consume
  2. Transpiling the entire dependency tree will make your project slower
  3. Differing behaviours between TypeScript and node.js (e.g. ES2015 modules) can result in a project that works until you decide to support a feature natively from node.js

paths and baseUrl

You can use ts-node together with tsconfig-paths to load modules according to the paths section in tsconfig.json.

{
  "ts-node": {
    // Do not forget to `npm i -D tsconfig-paths`
    "require": ["tsconfig-paths/register"]
  }
}

Why is this not built-in to ts-node?

The official TypeScript Handbook explains the intended purpose for "paths" in "Additional module resolution flags".

The TypeScript compiler has a set of additional flags to inform the compiler of transformations that are expected to happen to the sources to generate the final output.

It is important to note that the compiler will not perform any of these transformations; it just uses these pieces of information to guide the process of resolving a module import to its definition file.

This means "paths" are intended to describe mappings that the build tool or runtime already performs, not to tell the build tool or runtime how to resolve modules. In other words, they intend us to write our imports in a way node already understands. For this reason, ts-node does not modify node's module resolution behavior to implement "paths" mappings.

Help! My Types Are Missing!

ts-node does not use files, include or exclude, by default. This is because a large majority projects do not use all of the files in a project directory (e.g. Gulpfile.ts, runtime vs tests) and parsing every file for types slows startup time. Instead, ts-node starts with the script file (e.g. ts-node index.ts) and TypeScript resolves dependencies based on imports and references.

For global definitions, you can use the typeRoots compiler option. This requires that your type definitions be structured as type packages (not loose TypeScript definition files). More details on how this works can be found in the TypeScript Handbook.

Example tsconfig.json:

{
  "compilerOptions": {
    "typeRoots" : ["./node_modules/@types", "./typings"]
  }
}

Example project structure:

<project_root>/
-- tsconfig.json
-- typings/
  -- <module_name>/
    -- index.d.ts

Example module declaration file:

declare module '<module_name>' {
    // module definitions go here
}

For module definitions, you can use paths:

{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "custom-module-type": ["types/custom-module-type"]
    }
  }
}

An alternative approach for definitions of third-party libraries are triple-slash directives. This may be helpful if you prefer not to change your TypeScript compilerOptions or structure your custom type definitions when using typeRoots. Below is an example of the triple-slash directive as a relative path within your project:

/// <reference types="./types/untyped_js_lib" />
import UntypedJsLib from "untyped_js_lib"

Tip: If you must use files, include, or exclude, enable --files flags or set TS_NODE_FILES=true.

Third-party compilers

Some projects require a patched typescript compiler which adds additional features. For example, ttypescript and ts-patch add the ability to configure custom transformers. These are drop-in replacements for the vanilla typescript module and implement the same API.

For example, to use ttypescript and ts-transformer-keys, add this to your tsconfig.json:

{
  "ts-node": {
    // This can be omitted when using ts-patch
    "compiler": "ttypescript"
  },
  "compilerOptions": {
    // plugin configuration is the same for both ts-patch and ttypescript
    "plugins": [
      { "transform": "ts-transformer-keys/transformer" }
    ]
  }
}

Third-party transpilers

In transpile-only mode, we skip typechecking to speed up execution time. You can go a step further and use a third-party transpiler to transform TypeScript into JavaScript even faster. You will still benefit from ts-node's automatic tsconfig.json discovery, sourcemap support, and global ts-node CLI. Integrations can automatically derive an appropriate configuration from your existing tsconfig.json which simplifies project boilerplate.

What is the difference between a compiler and a transpiler?

For our purposes, a compiler implements TypeScript's API and can perform typechecking. A third-party transpiler does not. Both transform TypeScript into JavaScript.

Bundled swc integration

We have bundled an experimental swc integration.

swc is a TypeScript-compatible transpiler implemented in Rust. This makes it an order of magnitude faster than transpileModule.

To use it, first install @swc/core or @swc/wasm. If using importHelpers, also install @swc/helpers.

npm i -D @swc/core @swc/helpers

Then add the following to your tsconfig.json.

{
  "ts-node": {
    "transpileOnly": true,
    "transpiler": "ts-node/transpilers/swc-experimental"
  }
}

swc uses @swc/helpers instead of tslib. If you have enabled importHelpers, you must also install @swc/helpers.

Writing your own integration

To write your own transpiler integration, check our API docs.

Integrations are require()d, so they can be published to npm. The module must export a create function matching the TranspilerModule interface.

Module type overrides

When deciding between CommonJS and native ECMAScript modules, ts-node defaults to matching vanilla node and tsc behavior. This means TypeScript files are transformed according to your tsconfig.json "module" option and executed according to node's rules for the package.json "type" field.

In some projects you may need to override this behavior for some files. For example, in a webpack project, you may have package.json configured with "type": "module" and tsconfig.json with "module": "esnext". However, webpack uses our CommonJS hook to execute your webpack.config.ts, so you need to force your webpack config and any supporting scripts to execute as CommonJS.

In these situations, our moduleTypes option lets you override certain files, forcing execution as CommonJS or ESM. Node supports similar overriding via .cjs and .mjs file extensions, but .ts files cannot use them. moduleTypes achieves the same effect, and also overrides your tsconfig.json "module" config appropriately.

The following example tells ts-node to execute a webpack config as CommonJS:

{
  "ts-node": {
    "transpileOnly": true,
    "moduleTypes": {
      "webpack.config.ts": "cjs",
      // Globs are also supported with the same behavior as tsconfig "include"
      "webpack-config-scripts/**/*": "cjs"
    }
  },
  "compilerOptions": {
    "module": "es2020",
    "target": "es2020"
  }
}

Each key is a glob pattern with the same syntax as tsconfig's "include" array. When multiple patterns match the same file, the last pattern takes precedence.

  • cjs overrides matches files to compile and execute as CommonJS.
  • esm overrides matches files to compile and execute as native ECMAScript modules.
  • package resets either of the above to default behavior, which obeys package.json "type" and tsconfig.json "module" options.

Caveats

Files with an overridden module type are transformed with the same limitations as isolatedModules. This will only affect rare cases such as using const enums with preserveConstEnums disabled.

This feature is meant to facilitate scenarios where normal compilerOptions and package.json configuration is not possible. For example, a webpack.config.ts cannot be given its own package.json to override "type". Wherever possible you should favor using traditional package.json and tsconfig.json configurations.

Recipes

Watching and Restarting

TypeScript Node compiles source code via require(), watching files and code reloads are out of scope for the project. If you want to restart the ts-node process on file change, existing node.js tools such as nodemon, onchange and node-dev work.

There's also ts-node-dev, a modified version of node-dev using ts-node for compilation that will restart the process on file change.

AVA

Assuming you are configuring AVA via your package.json, add one of the following configurations.

CommonJS

Use this configuration if your package.json does not have "type": "module".

{
  "ava": {
    "extensions": [
      "ts"
    ],
    "require": [
      "ts-node/register"
    ]
  }
}

Native ECMAScript modules

This configuration is necessary if your package.json has "type": "module".

{
  "ava": {
    "extensions": {
      "ts": "module"
    },
    "nonSemVerExperiments": {
      "configurableModuleFormat": true
    },
    "nodeArguments": [
      "--loader=ts-node/esm"
    ]
  }
}

Gulp

ts-node support is built-in to gulp.

# Create a `gulpfile.ts` and run `gulp`.
gulp

See also: https://gulpjs.com/docs/en/getting-started/javascript-and-gulpfiles#transpilation

IntelliJ and Webstorm

Create a new Node.js configuration and add -r ts-node/register to "Node parameters."

Note: If you are using the --project <tsconfig.json> command line argument as per the Configuration Options, and want to apply this same behavior when launching in IntelliJ, specify under "Environment Variables": TS_NODE_PROJECT=<tsconfig.json>.

Mocha

Mocha 7 and newer

mocha --require ts-node/register --extensions ts,tsx --watch --watch-files src 'tests/**/*.{ts,tsx}' [...args]

Or specify options via your mocha config file.

{
  // Specify "require" for CommonJS
  "require": "ts-node/register",
  // Specify "loader" for native ESM
  "loader": "ts-node/esm",
  "extensions": ["ts", "tsx"],
  "spec": [
    "tests/**/*.spec.*"
  ],
  "watch-files": [
    "src"
  ]
}

See also: https://mochajs.org/#configuring-mocha-nodejs

Mocha <=6

mocha --require ts-node/register --watch-extensions ts,tsx "test/**/*.{ts,tsx}" [...args]

Note: --watch-extensions is only used in --watch mode.

Tape

ts-node node_modules/tape/bin/tape [...args]

Visual Studio Code

Create a new Node.js debug configuration, add -r ts-node/register to node args and move the program to the args list (so VS Code doesn't look for outFiles).

{
    "configurations": [{
        "type": "node",
        "request": "launch",
        "name": "Launch Program",
        "runtimeArgs": [
            "-r",
            "ts-node/register"
        ],
        "args": [
            "${workspaceFolder}/src/index.ts"
        ]
    }],
}

Note: If you are using the --project <tsconfig.json> command line argument as per the Configuration Options, and want to apply this same behavior when launching in VS Code, add an "env" key into the launch configuration: "env": { "TS_NODE_PROJECT": "<tsconfig.json>" }.

Other

In many cases, setting NODE_OPTIONS will enable ts-node within other node tools, child processes, and worker threads.

NODE_OPTIONS="-r ts-node/register"

Or, if you require native ESM support:

NODE_OPTIONS="--loader ts-node/esm"

This tells any node processes which receive this environment variable to install ts-node's hooks before executing other code.

License

ts-node is licensed under the MIT license. MIT

ts-node includes source code from Node.js which is licensed under the MIT license. Node.js license information

ts-node includes source code from the TypeScript compiler which is licensed under the Apache License 2.0. TypeScript license information