The package that linked you here is now pure ESM. It cannot be require()
'd from CommonJS.
This means you have the following choices:
- Use ESM yourself. (preferred)
Useimport foo from 'foo'
instead ofconst foo = require('foo')
to import the package. You also need to put"type": "module"
in your package.json and more. Follow the below guide. - If the package is used in an async context, you could use
await import(…)
from CommonJS instead ofrequire(…)
. - Stay on the existing version of the package until you can move to ESM.
- Since Node.js 22, you may be able to
require()
ESM modules. However, I strongly recommend moving to ESM instead.
You also need to make sure you're on the latest minor version of Node.js. At minimum Node.js 16.
I would strongly recommend moving to ESM. ESM can still import CommonJS packages, but CommonJS packages cannot import ESM packages synchronously.
My repos are not the place to ask ESM/TypeScript/Webpack/Jest/ts-node/CRA support questions.
- Add
"type": "module"
to your package.json. - Replace
"main": "index.js"
with"exports": "./index.js"
in your package.json. - Update the
"engines"
field in package.json to Node.js 18:"node": ">=18"
. - Remove
'use strict';
from all JavaScript files. - Replace all
require()
/module.export
withimport
/export
. - Use only full relative file paths for imports:
import x from '.';
→import x from './index.js';
. - If you have a TypeScript type definition (for example,
index.d.ts
), update it to use ESM imports/exports. - Use the
node:
protocol for Node.js built-in imports.
Sidenote: If you're looking for guidance on how to add types to your JavaScript package, check out my guide.
Yes, but you need to convert your project to output ESM. See below.
Quick steps:
- Make sure you are using TypeScript 4.7 or later.
- Add
"type": "module"
to your package.json. - Replace
"main": "index.js"
with"exports": "./index.js"
in your package.json. - Update the
"engines"
field in package.json to Node.js 18:"node": ">=18"
. - Add
"module": "node16", "moduleResolution": "node16"
to your tsconfig.json. (Example)moduleResolution
must be set tonode16
ornodenext
, NOTnode
!
- Use only full relative file paths for imports:
import x from '.';
→import x from './index.js';
. - Remove
namespace
usage and useexport
instead. - Use the
node:
protocol for Node.js built-in imports. - You must use a
.js
extension in relative imports even though you're importing.ts
files.
If you use ts-node
, follow this guide. Example config.
Electron supports ESM as of Electron 28. Please read this.
The problem is either Webpack or your Webpack configuration. First, ensure you are on the latest version of Webpack. Please don't open an issue on my repo. Try asking on Stack Overflow or open an issue the Webpack repo.
Upgrade to Next.js 12 which has full ESM support.
If you have decided to make your project ESM ("type": "module"
in your package.json), make sure you have "module": "node16"
in your tsconfig.json and that all your import statements to local files use the .js
extension, not .ts
or no extension.
I would recommend tsx
instead.
Follow this guide and ensure you are on the latest version of ts-node
.
Create React App doesn't yet fully support ESM. I would recommend opening an issue on their repo with the problem you have encountered. One known issue is #10933.
Follow this guide.
We got you covered with this ESLint rule. You should also use this rule.
Node.js 20.11+
Use import.meta.dirname
and import.meta.filename
.
Older Node.js versions
import {fileURLToPath} from 'node:url';
import path from 'node:path';
const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(fileURLToPath(import.meta.url));
However, in most cases, this is better:
import {fileURLToPath} from 'node:url';
const foo = fileURLToPath(new URL('foo.js', import.meta.url));
And many Node.js APIs accept URL directly, so you can just do this:
const foo = new URL('foo.js', import.meta.url);
There's no good way to do this yet. Not until we get ESM loader hooks. For now, this snippet can be useful:
const importFresh = async modulePath => import(`${modulePath}?x=${Date.now()}`);
const chalk = (await importFresh('chalk')).default;
Note: This will cause memory leaks, so only use it for testing, not in production. Also, it will only reload the imported module, not its dependencies.
Node.js 18.20+
import packageJson from './package.json' with {type: 'json'};
Older Node.js versions
import fs from 'node:fs/promises';
const packageJson = JSON.parse(await fs.readFile('package.json'));
My general rule is that if something exports a single main thing, it should be a default export.
Keep in mind that you can combine a default export with named exports when it makes sense:
import readJson, {JSONError} from 'read-json';
Here, we had exported the main thing readJson
, but we also exported an error as a named export.
If your package has both an asynchronous and synchronous main API, I would recommend using named exports:
import {readJson, readJsonSync} from 'read-json';
This makes it clear to the reader that the package exports multiple main APIs. We also follow the Node.js convention of suffixing the synchronous API with Sync
.
I have noticed a bad pattern of packages using overly generic names for named exports:
import {parse} from 'parse-json';
This forces the consumer to either accept the ambiguous name (which might cause naming conflicts) or rename it:
import {parse as parseJson} from 'parse-json';
Instead, make it easy for the user:
import {parseJson} from 'parse-json';
With ESM, I now prefer descriptive named exports more often than a namespace default export:
CommonJS (before):
const isStream = require('is-stream');
isStream.writable(…);
ESM (now):
import {isWritableStream} from 'is-stream';
isWritableStream(…);
@ljharb
This is simply untrue. Runtime identity issues are just one symptom of the dual package hazard. If you are bundling, consuming the ESM and CJS formats of the same code in different parts of your code base / dependency graph result in the same code being bundled twice, which slows your builds, and increases the download and parse times for users loading the web app. If you are not bundling, loading and parsing more code still has a performance cost.
Technically not the dual package hazard, but another downside regardless, is if every package in
node_modules
duplicated it's API in seperate ESM and CJS files,node_modules
takes up considerably more disk space.node_modules
install size is a serious problem the industry is facing; it slows installations in CI or for deployments, and increases disk space usage increasing costs or exceeding environment limits (particularly for serverless).@OmgImAlexis
There are good reasons automatic file extension resolution was dropped from the final Node.js ESM system, and it isn't a thing in Deno or browsers either. It's a bad idea. Looking up all the possible resolutions is prohibitive if the modules are imported using HTTP imports over network; either in a server environment (Deno) or in browsers for apps using ESM for real on the client. It also significantly complicates and slows a lot of dev tooling that statically analyses imports. For an example of just one tool, look at all the extra complexity supporting it added to
find-unused-exports
:--resolve-file-extensions
--resolve-index-files
resolveFileExtensions
resolveIndexFiles