@esbuild-kit/cjs-loader

What is @esbuild-kit/cjs-loader?

@esbuild-kit/cjs-loader is an npm package that allows you to use ES modules (ESM) in CommonJS (CJS) environments. It leverages esbuild to transpile ESM to CJS on the fly, enabling seamless integration of modern JavaScript modules in older Node.js projects.

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

Transpile ESM to CJS

This feature allows you to transpile ES modules to CommonJS on the fly. By registering the loader, you can require ESM files in a CJS environment.

const { register } = require('@esbuild-kit/cjs-loader');
register();
const esmModule = require('./esmModule.mjs');
console.log(esmModule);

Custom Loader Options

You can customize the loader options such as the target ECMAScript version and the output format. This provides flexibility in how the ESM is transpiled to CJS.

const { register } = require('@esbuild-kit/cjs-loader');
register({ target: 'es2017', format: 'cjs' });
const esmModule = require('./esmModule.mjs');
console.log(esmModule);

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

esm

The 'esm' package allows you to use ES modules in Node.js without the need for a build step. It provides a seamless way to load ESM in a CJS environment, similar to @esbuild-kit/cjs-loader, but without leveraging esbuild for transpilation.

babel-register

The 'babel-register' package hooks into Node.js require to transpile files on the fly using Babel. It supports a wide range of JavaScript syntax transformations, including ESM to CJS, but may have a larger performance overhead compared to @esbuild-kit/cjs-loader.

ts-node

The 'ts-node' package allows you to run TypeScript files directly in Node.js. It can also handle ESM to CJS transpilation when used with appropriate TypeScript configurations. It is more focused on TypeScript but can be used for similar purposes.

README

cjs-loader

Node.js require() hook for loading ESM & TypeScript.

Features

• Transforms ESM & TypeScript to CommonJS on demand
• Supports TS extensions .cjs & .mjs (.cts & .mts)
• Cached for performance boost
• Supports Node.js v12.16.2+
• Handles node: import prefixes
• Resolves tsconfig.json paths

Protip: use with esm-loader or tsx

cjs-loader only transforms CommonJS modules (.cjs/.cts or .js files in commonjs type packages).

To hook into import() calls or ES modules (.mjs/.mts extensions or .js files in module type packages), use this with esm-loader.

Alternatively, use tsx to handle them both automatically.

Install

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

Usage

Pass @esbuild-kit/cjs-loader into the --require flag

node -r @esbuild-kit/cjs-loader ./file.js

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 -r @esbuild-kit/cjs-loader ./file.js

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 -r @esbuild-kit/cjs-loader ./file.js

Related

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

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

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