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ESM

Version 3.0.0 of @oclif/core officially supports ESM plugin development and CJS/ESM interoperability, meaning that you can have a root plugin written with CJS and your plugins written in ESM or vice versa.

Interoperability Overview​

Here's a high level overview of ESM/CJS interoperability:

ESM Root plugin​

✅ Install CJS plugins

✅ Install ESM plugins

✅ Link CJS plugins

⚠️ Link ESM plugins

  • Auto-compilation will not work with linked ESM plugins. Instead, oclif will use the plugin's compiled source - this means that you must compile the plugin yourself before executing any of the commands. We plan to support this again once the node ecosystem offers more comprehensive native support for ESM.

CJS Root plugin​

✅ Install CJS plugins

✅ Install ESM plugins

✅ Link CJS plugins

⚠️ Link ESM plugins

  • Auto-compilation will not work with linked ESM plugins. Instead, oclif will use the plugin's compiled source - this means that you must compile the plugin yourself before executing any of the commands. We plan to support this again once the node ecosystem offers more comprehensive native support for ESM.

Creating an ESM plugin​

To generate a new ESM plugin from the hello-world-esm template run the oclif generate command and select ESM when it prompts you to select a module type:

$ npx oclif generate my-esm-plugin
? Select a module type
  CommonJS
❯ ESM

Migrating a CJS plugin to ESM​

Update bin scripts​

First you will need to update the bin scripts under the bin directory.

bin/dev → bin/dev.js​

Rename bin/dev to bin/dev.js and replace the existing code with the following:

#!/usr/bin/env -S node --loader ts-node/esm --no-warnings=ExperimentalWarning

import {execute} from '@oclif/core'

await execute({development: true, dir: import.meta.url})

This leverages oclif's execute function which handles all the development setup for you. You no longer need set the NODE_ENV env var or register the project with ts-node. You can still adjust oclif settings before executing the CLI. For example,

#!/usr/bin/env -S node --loader ts-node/esm --no-warnings=ExperimentalWarning

import {execute, settings} from '@oclif/core'

settings.performanceEnabled = true

await execute({development: true, dir: import.meta.url})

bin/run → bin/run.js​

Rename bin/run to bin/run.js and replace the existing code with the following:

#!/usr/bin/env node

import {execute} from '@oclif/core'

await execute({dir: import.meta.url})

Update tsconfig.json​

After updating the bin scripts you now need to update the tsconfig.json to include the following options:

{
  "compilerOptions": {
    "module": "ES2020",
    "moduleResolution": "node16",
  },
  "ts-node": {
    "esm": true
  }
}

Update package.json to "module" type​

Add "type": "module" to your package.json so that your files will be loaded as ESM modules

Update references to bin scripts​

You will need to update the references to your bin scripts to the bin scripts with the .js extension. In the package.json you will need to update the bin like so:

  "bin": {
    "my-cli": "./bin/run"
  },

to

  "bin": {
    "my-cli": "./bin/run.js"
  },

You may have references to the bin scripts in your .vscode/launch.json or in the scripts of your package.json. You'll need to update these as well.

Update mocharc settings​

In order for your mocha tests to run, you'll need to make a couple of changes:

  1. Add the following to the .mocharc.json
{
  "node-option": [
    "loader=ts-node/esm"
  ]
}
  1. Update test/helpers/init.js

If your plugin was generated oclif generate then you likely have a test/helpers/init.js file that needs to be updated. You can either update the file extension to .cjs or update the require at the top of the file to an import,

import path from 'node:path'

Alternatively, you can safely delete this file since it's no longer necessary.