ts-node
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    10.8.0 • Public • Published

    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

    Command Line

    # 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 --transpileOnly
    ts-node-transpile-only script.ts
    
    # Equivalent to ts-node --cwdMode
    ts-node-cwd script.ts
    
    # Equivalent to ts-node --esm
    ts-node-esm script.ts

    Shebang

    To write scripts with maximum portability, specify options in your tsconfig.json and omit them from the shebang.

    #!/usr/bin/env ts-node
    
    // ts-node options are read from tsconfig.json
    
    console.log("Hello, world!")

    Including options within the shebang requires the env -S flag, which is available on recent versions of env. (compatibility)

    #!/usr/bin/env -S ts-node --files
    // This shebang works on Mac and Linux with newer versions of env
    // Technically, Mac allows omitting `-S`, but Linux requires it

    To test your version of env for compatibility with -S:

    # Note that these unusual quotes are necessary
    /usr/bin/env --debug '-S echo foo bar'

    node flags and other tools

    You can register ts-node without using our CLI: node -r ts-node/register and node --loader ts-node/esm

    In many cases, setting NODE_OPTIONS will enable ts-node within other node tools, child processes, and worker threads. This can be combined with other node flags.

    NODE_OPTIONS="-r ts-node/register --no-warnings" node ./index.ts

    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.

    If you are invoking node directly, you can avoid the environment variable and pass those flags to node.

    node --loader ts-node/esm --inspect ./index.ts

    Programmatic

    You can require ts-node and register the loader for future requires by using require('ts-node').register({ /* options */ }).

    Check out our API for more features.

    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 --skipProject 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 --cwdMode 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 --showConfig 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

    All command-line flags support both --camelCase and --hyphen-case.

    Most options can be declared in your tsconfig.json: Configuration via tsconfig.json

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

    ts-node supports --project and --showConfig similar to the tsc CLI.

    Environment variables, where available, are in ALL_CAPS

    CLI Options

    help

    ts-node --help

    Prints the help text

    version

    ts-node -v
    ts-node -vvv

    Prints the version. -vv includes node and typescript compiler versions. -vvv includes absolute paths to ts-node and typescript installations.

    eval

    ts-node -e <typescript code>
    # Example
    ts-node -e 'console.log("Hello world!")'

    Evaluate code

    print

    ts-node -p -e <typescript code>
    # Example
    ts-node -p -e '"Hello world!"'

    Print result of --eval

    interactive

    ts-node -i

    Opens the REPL even if stdin does not appear to be a terminal

    esm

    ts-node --esm
    ts-node-esm

    Bootstrap with the ESM loader, enabling full ESM support

    TSConfig Options

    project

    ts-node -P <path/to/tsconfig>
    ts-node --project <path/to/tsconfig>

    Path to tsconfig file.

    Note the uppercase -P. This is different from tsc's -p/--project option.

    Environment: TS_NODE_PROJECT

    skipProject

    ts-node --skipProject

    Skip project config resolution and loading

    Default: false
    Environment: TS_NODE_SKIP_PROJECT

    cwdMode

    ts-node -c
    ts-node --cwdMode
    ts-node-cwd

    Resolve config relative to the current directory instead of the directory of the entrypoint script

    compilerOptions

    ts-node -O <json compilerOptions>
    ts-node --compilerOptions <json compilerOptions>

    JSON object to merge with compiler options

    Environment: TS_NODE_COMPILER_OPTIONS

    showConfig

    ts-node --showConfig

    Print resolved tsconfig.json, including ts-node options, and exit

    Typechecking

    transpileOnly

    ts-node -T
    ts-node --transpileOnly

    Use TypeScript's faster transpileModule

    Default: false
    Environment: TS_NODE_TRANSPILE_ONLY

    typeCheck

    ts-node --typeCheck

    Opposite of --transpileOnly

    Default: true
    Environment: TS_NODE_TYPE_CHECK

    compilerHost

    ts-node -H
    ts-node --compilerHost

    Use TypeScript's compiler host API

    Default: false
    Environment: TS_NODE_COMPILER_HOST

    files

    ts-node --files

    Load files, include and exclude from tsconfig.json on startup. This may avoid certain typechecking failures. See Missing types for details.

    Default: false
    Environment: TS_NODE_FILES

    ignoreDiagnostics

    ts-node -D <code,code>
    ts-node --ignoreDiagnostics <code,code>

    Ignore TypeScript warnings by diagnostic code

    Environment: TS_NODE_IGNORE_DIAGNOSTICS

    Transpilation Options

    ignore

    ts-node -I <regexp matching ignored files>
    ts-node --ignore <regexp matching ignored files>

    Override the path patterns to skip compilation

    Default: /node_modules/
    Environment: TS_NODE_IGNORE

    skipIgnore

    ts-node --skipIgnore

    Skip ignore checks

    Default: false
    Environment: TS_NODE_SKIP_IGNORE

    compiler

    ts-node -C <name>
    ts-node --compiler <name>

    Specify a custom TypeScript compiler

    Default: typescript
    Environment: TS_NODE_COMPILER

    swc

    ts-node --swc

    Transpile with swc. Implies --transpileOnly

    Default: false

    transpiler

    ts-node --transpiler <name>
    # Example
    ts-node --transpiler ts-node/transpilers/swc

    Use a third-party, non-typechecking transpiler

    preferTsExts

    ts-node --preferTsExts

    Re-order file extensions so that TypeScript imports are preferred

    Default: false
    Environment: TS_NODE_PREFER_TS_EXTS

    Diagnostic Options

    logError

    ts-node --logError

    Logs TypeScript errors to stderr instead of throwing exceptions

    Default: false
    Environment: TS_NODE_LOG_ERROR

    pretty

    ts-node --pretty

    Use pretty diagnostic formatter

    Default: false
    Environment: TS_NODE_PRETTY

    TS_NODE_DEBUG

    TS_NODE_DEBUG=true ts-node

    Enable debug logging

    Advanced Options

    require

    ts-node -r <module name or path>
    ts-node --require <module name or path>

    Require a node module before execution

    cwd

    ts-node --cwd <path/to/directory>

    Behave as if invoked in this working directory

    Default: process.cwd()
    Environment: TS_NODE_CWD

    emit

    ts-node --emit

    Emit output files into .ts-node directory. Requires --compilerHost

    Default: false
    Environment: TS_NODE_EMIT

    scope

    ts-node --scope

    Scope compiler to files within scopeDir. Anything outside this directory is ignored.

    *Default: false
    Environment: TS_NODE_SCOPE

    scopeDir

    ts-node --scopeDir <path/to/directory>

    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

    moduleTypes

    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

    TS_NODE_HISTORY=<path/to/history/file> ts-node

    Path to history file for REPL

    Default: ~/.ts_node_repl_history

    noExperimentalReplAwait

    ts-node --noExperimentalReplAwait

    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

    experimentalResolver

    Enable experimental hooks that re-map imports and require calls to support:

    • resolves .js to .ts, so that import "./foo.js" will execute foo.ts
    • resolves .cjs to .cts
    • resolves .mjs to .mts
    • allows including file extensions in CommonJS, for consistency with ESM where this is often mandatory

    In the future, this hook will also support:

    • baseUrl, paths
    • rootDirs
    • outDir to rootDir mappings for composite projects and monorepos

    For details, see #1514.

    Default: false, but will likely be enabled by default in a future version
    Can only be specified via tsconfig.json or API.

    experimentalSpecifierResolution

    ts-node --experimentalSpecifierResolution node

    Like node's --experimental-specifier-resolution, but can also be set in your tsconfig.json for convenience. Requires esm to be enabled.

    Default: explicit

    API Options

    The API includes additional options not shown here.

    SWC

    SWC support is built-in via the --swc flag or "swc": true tsconfig option.

    SWC is a TypeScript-compatible transpiler implemented in Rust. This makes it an order of magnitude faster than vanilla transpileOnly.

    To use it, first install @swc/core or @swc/wasm. If using importHelpers, also install @swc/helpers. If target is less than "es2015" and using async/await or generator functions, also install regenerator-runtime.

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

    Then add the following to your tsconfig.json.

    {
      "ts-node": {
        "swc": true
      }
    }

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

    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
    node -r ts-node/register
    NODE_OPTIONS="ts-node/register" node
    require('ts-node').register({/* options */})
    Use any of:
    ts-node --esm
    ts-node-esm
    Set "esm": true in tsconfig.json
    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
      },
      "ts-node": {
        // Tell ts-node CLI to install the --loader automatically, explained below
        "esm": true
      }
    }

    You must also ensure node is passed --loader. The ts-node CLI will do this automatically with our esm option.

    Note: --esm must spawn a child process to pass it --loader. This may change if node adds the ability to install loader hooks into the current process.

    # pass the flag
    ts-node --esm
    # Use the convenience binary
    ts-node-esm
    # or add `"esm": true` to your tsconfig.json to make it automatic
    ts-node

    If you are not using our CLI, pass the loader flag to node.

    node --loader ts-node/esm ./index.ts
    # Or via environment variable
    NODE_OPTIONS="--loader ts-node/esm" node ./index.ts

    Troubleshooting

    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 --showConfig. 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 --showConfig
    {
      "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"
      }
    }

    Common 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.

    ERR_REQUIRE_ESM

    This error is thrown by node when a module is require()d, but node believes it should execute as native ESM. This can happen for a few reasons:

    • You have installed an ESM dependency but your own code compiles to CommonJS.
      • Solution: configure your project to compile and execute as native ESM. Docs
      • Solution: downgrade the dependency to an older, CommonJS version.
    • You have moved your project to ESM but still have a config file, such as webpack.config.ts, which must be executed as CommonJS
      • Solution: if supported by the relevant tool, rename your config file to .cts
      • Solution: Configure a module type override. Docs
    • You have a mix of CommonJS and native ESM in your project
      • Solution: double-check all package.json "type" and tsconfig.json "module" configuration Docs
      • Solution: consider simplifying by making your project entirely CommonJS or entirely native ESM

    ERR_UNKNOWN_FILE_EXTENSION

    This error is thrown by node when a module has an unrecognized file extension, or no extension at all, and is being executed as native ESM. This can happen for a few reasons:

    • You are using a tool which has an extensionless binary, such as mocha.
      • CommonJS supports extensionless files but native ESM does not.
      • Solution: upgrade to ts-node >=v10.6.0, which implements a workaround.
    • Our ESM loader is not installed.
      • Solution: Use ts-node-esm, ts-node --esm, or add "ts-node": {"esm": true} to your tsconfig.json. Docs
    • You have moved your project to ESM but still have a config file, such as webpack.config.ts, which must be executed as CommonJS
      • Solution: if supported by the relevant tool, rename your config file to .cts
      • Solution: Configure a module type override. Docs

    Missing Types

    ts-node does not eagerly load files, include or exclude by default. This is because a large majority of 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.

    Occasionally, this optimization leads to missing types. Fortunately, there are other ways to include them in typechecking.

    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"]
        }
      }
    }

    Another option is triple-slash directives. This may be helpful if you prefer not to change your compilerOptions or structure your type definitions for typeRoots. Below is an example of a triple-slash directive as a relative path within your project:

    /// <reference path="./types/lib_greeter" />
    import {Greeter} from "lib_greeter"
    const g = new Greeter();
    g.sayHello();

    If none of the above work, and you must use files, include, or exclude, enable our files option.

    npx, yarn dlx, and node_modules

    When executing TypeScript with npx or yarn dlx, the code resides within a temporary node_modules directory.

    The contents of node_modules are ignored by default. If execution fails, enable skipIgnore.

    Performance

    These tricks will make ts-node faster.

    Skip typechecking

    It is often better to use tsc --noEmit to typecheck as part of your tests or linting. In these cases, ts-node can skip typechecking.

    • Enable swc
      • This is by far the fastest option
    • Enable transpileOnly to skip typechecking without swc

    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.

    We also register a few other hooks to apply sourcemaps to stack traces and remap from .js imports to .ts.

    Ignored files

    ts-node transforms certain files and ignores others. We refer to this mechanism as "scoping." There are various options to configure scoping, so that ts-node transforms only the files in your project.

    Warning:

    An ignored file can still be executed by node.js. Ignoring a file means we do not transform it from TypeScript into JavaScript, but it does not prevent execution.

    If a file requires transformation but is ignored, node may either fail to resolve it or attempt to execute it as vanilla JavaScript. This may cause syntax errors or other failures, because node does not understand TypeScript type syntax nor bleeding-edge ECMAScript features.

    File extensions

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

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

    Warning:

    When ts-node is used with allowJs, all non-ignored JavaScript files are transformed by ts-node.

    Skipping node_modules

    By default, ts-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

    If you need to import uncompiled TypeScript in node_modules, use --skipIgnore or TS_NODE_SKIP_IGNORE to bypass this restriction.

    Skipping pre-compiled TypeScript

    If a compiled JavaScript file with the same name as a TypeScript file already exists, the TypeScript file will be ignored. ts-node will import the pre-compiled JavaScript.

    To force ts-node to import the TypeScript source, not the precompiled JavaScript, use --preferTsExts.

    Scope by directory

    Our scope and scopeDir options will limit transformation to files within a directory.

    Ignore by regexp

    Our ignore option will ignore files matching one or more regular expressions.

    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.

    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" }
        ]
      }
    }

    Transpilers

    ts-node supports third-party transpilers as plugins. Transpilers such as swc can transform TypeScript into JavaScript much faster than the TypeScript compiler. You will still benefit from ts-node's automatic tsconfig.json discovery, sourcemap support, and global ts-node CLI. Plugins 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.

    Third-party plugins

    The transpiler option allows using third-party transpiler plugins with ts-node. transpiler must be given the name of a module which can be require()d. The built-in swc plugin is exposed as ts-node/transpilers/swc.

    For example, to use a hypothetical "speedy-ts-compiler", first install it into your project: npm install speedy-ts-compiler

    Then add the following to your tsconfig:

    {
      "ts-node": {
        "transpileOnly": true,
        "transpiler": "speedy-ts-compiler"
      }
    }

    Write your own plugin

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

    Plugins are require()d by ts-node, so they can be a local script or a node module published to npm. The module must export a create function described by our TranspilerModule interface. create is invoked by ts-node at startup to create one or more transpiler instances. The instances are used to transform TypeScript into JavaScript.

    For a working example, check out out our bundled swc plugin: https://github.com/TypeStrong/ts-node/blob/main/src/transpilers/swc.ts

    Module type overrides

    Wherever possible, it is recommended to use TypeScript's NodeNext or Node16 mode instead of the options described in this section. Setting "module": "NodeNext" and using the .cts file extension should work well for most projects.

    When deciding how a file should be compiled and executed -- as either CommonJS or native ECMAScript module -- ts-node matches 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. Set "module": "NodeNext" and everything should work.

    In rare cases, you may need to override this behavior for some files. For example, some tools read a name-of-tool.config.ts and require that file to execute as CommonJS. If you have package.json configured with "type": "module" and tsconfig.json with "module": "esnext", the config is native ECMAScript by default and will raise an error. You will need to force the config and any supporting scripts to execute as CommonJS.

    In these situations, our moduleTypes option can override certain files to be CommonJS or ESM. Similar overriding is possible by using .mts, .cts, .cjs and .mjs file extensions. moduleTypes achieves the same effect for .ts and .js files, 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.

    API

    ts-node's complete API is documented here: API Docs

    Here are a few highlights of what you can accomplish:

    • create() creates ts-node's compiler service without registering any hooks.
    • createRepl() creates an instance of our REPL service, so you can create your own TypeScript-powered REPLs.
    • createEsmHooks() creates our ESM loader hooks, suitable for composing with other loaders or augmenting with additional features.

    Recipes

    Watching and restarting

    ts-node focuses on adding first-class TypeScript support to node. 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. Note that ts-node-dev is incompatible with our native ESM loader.

    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

    Install

    npm i ts-node

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