@esbuild-kit/esm-loader

What is @esbuild-kit/esm-loader?

@esbuild-kit/esm-loader is an npm package that allows you to use ES modules (ESM) in Node.js environments that do not natively support them. It leverages esbuild to transpile and load ESM code, making it easier to work with modern JavaScript syntax and features.

What are @esbuild-kit/esm-loader's main functionalities?

Transpile ESM to CommonJS

This feature allows you to import and use CommonJS modules in an ESM context. The code sample demonstrates how to use the `createRequire` function to require a CommonJS module in an ESM file.

import { createRequire } from 'module';
const require = createRequire(import.meta.url);
const { exampleFunction } = require('./example-file.js');
exampleFunction();

Load TypeScript files

This feature allows you to directly import and use TypeScript files in your Node.js project. The code sample shows how to import a TypeScript file and call a function from it.

import { exampleFunction } from './example-file.ts';
exampleFunction();

Support for JSX/TSX

This feature enables you to import and use JSX/TSX files in your Node.js project. The code sample demonstrates how to import a TSX file and render a React component.

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App.tsx';

ReactDOM.render(<App />, document.getElementById('root'));

Other packages similar to @esbuild-kit/esm-loader

ts-node

ts-node is a TypeScript execution engine and REPL for Node.js. It allows you to run TypeScript code directly without precompiling. Compared to @esbuild-kit/esm-loader, ts-node focuses more on TypeScript execution and less on ESM support.

babel-register

babel-register is a package that hooks into Node.js require to compile files on the fly using Babel. It supports a wide range of JavaScript syntax and features. While it provides similar functionality to @esbuild-kit/esm-loader, it relies on Babel instead of esbuild for transpilation.

esm

esm is a package that enables ES module support in Node.js. It allows you to use ESM syntax in Node.js versions that do not natively support it. Compared to @esbuild-kit/esm-loader, esm is more focused on providing ESM support without additional transpilation features.

README

esm-loader

Node.js loader for loading TypeScript files.

Features

• Transforms TypeScript to ESM on demand
• Classic Node.js resolution (extensionless & directory imports)
• Cached for performance boost
• Supports Node.js v12.20.0+
• Handles node: import prefixes
• Resolves tsconfig.json paths
• Named imports from JSON modules

Protip: use with cjs-loader or tsx

esm-loader only transforms ES modules (.mjs/.mts extensions or .js files in module type packages).

To transform CommonJS files (.cjs/.cts extensions or .js files in commonjs type packages), use this with cjs-loader.

Alternatively, use tsx to handle them both automatically.

Install

npm install --save-dev @esbuild-kit/esm-loader

Usage

Pass @esbuild-kit/esm-loader into the --loader flag.

node --loader @esbuild-kit/esm-loader ./file.ts

TypeScript configuration

The following properties are used from tsconfig.json in the working directory:

• strict: Whether to transform to strict mode
• jsx: Whether to transform JSX

  Warning: When set to preserve, the JSX syntax will remain untransformed. To prevent Node.js from throwing a syntax error, chain another Node.js loader that can transform JSX to JS.

• jsxFactory: How to transform JSX
• jsxFragmentFactory: How to transform JSX Fragments
• jsxImportSource: Where to import JSX functions from
• allowJs: Whether to apply the tsconfig to JS files
• paths: For resolving aliases

Custom tsconfig.json path

By default, tsconfig.json will be detected from the current working directory.

To set a custom path, use the ESBK_TSCONFIG_PATH environment variable:

ESBK_TSCONFIG_PATH=./path/to/tsconfig.custom.json node --loader @esbuild-kit/esm-loader ./file.ts

Cache

Modules transformations are cached in the system cache directory (TMPDIR). Transforms are cached by content hash so duplicate dependencies are not re-transformed.

Set environment variable ESBK_DISABLE_CACHE to a truthy value to disable the cache:

ESBK_DISABLE_CACHE=1 node --loader @esbuild-kit/esm-loader ./file.ts

FAQ

Can it import JSON modules?

Yes. This loader transpiles JSON modules so it's also compatible with named imports.

Can it import ESM modules over network?

Node.js has built-in support for network imports behind the --experimental-network-imports flag.

You can pass it in with esm-loader:

node --loader @esbuild-kit/esm-loader --experimental-network-imports ./file.ts

Can it resolve files without an extension?

In ESM, import paths must be explicit (must include file name and extension).

For backwards compatibility, this loader adds support for classic Node resolution for extensions: .js, .json, .ts, .tsx, .jsx. Resolving a index file by the directory name works too.

import file from './file' // -> ./file.js
import directory from './directory' // -> ./directory/index.js

Can it use Node.js's CommonJS resolution algorithm?

ESM import resolution expects explicit import paths, whereas CommonJS resolution expects implicit imports (eg. extensionless & directory imports).

As a result of this change, Node.js changes how it imports a path that matches both a file and directory. In ESM, the directory would be imported, but in CJS, the file would be imported.

To use to the CommonJS resolution algorithm, use the --experimental-specifier-resolution=node flag.

node --loader @esbuild-kit/esm-loader --experimental-specifier-resolution=node ./file.ts

Related

• tsx - Node.js runtime powered by esbuild using @esbuild-kit/cjs-loader and @esbuild-kit/esm-loader.

• @esbuild-kit/cjs-loader - TypeScript & ESM to CJS transpiler using the Node.js loader API.

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