Node.js import hook to instantaneously transform TypeScript to ESM on demand using esbuild.

• 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

Tip:

esm-loader doesn't hook into require() calls or transform CommonJS files (.js in commonjs package, .cjs, .cts).

Use this with cjs-loader for CommonJS support. Alternatively, use tsx to handle them both automatically.

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

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

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

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

• jsxFactory
• jsxFragmentFactory

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/esm-loader ./file.ts

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

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

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

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

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

• 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.