How to include commonjs module in ES6 module node app?
Solution 1
Working with CommonJS modules is pretty straight forward.
You can only do default
exports from CommonJS modules.
import packageMain from 'commonjs-package'; // Works
import { method } from 'commonjs-package'; // Errors
This means that all commonjs exports will live on the packageMain
object, and you need to dot in to the packageMain object to pickup what you need.
packageMain.method1()
More info in the official nodejs docs
Solution 2
Since Node 13.10, there is another option, the most forward-looking one:
File an issue in the repo of the CommonJS library you'd like to use, persuading the maintainers to publish dual packages (ESM + CommonJS), using conditional exports.
For libraries written in TypeScript, generating dual packages is easy, and doesn't require Babel or rollup or any additional tools. Here's how I did it in local-iso-dt:
Relevant parts of package.json:
{
"name": "local-iso-dt",
"version": "3.1.0",
"description": "...",
"type": "commonjs",
"exports": {
"node": {
"import": "./index.mjs",
"require": "./index.js"
},
"default": "./index.mjs"
},
"main": "index.js",
"files": [
"index.ts",
"index.mjs",
"index.js"
],
"scripts": {
"clean": "rm index*.js index.mjs",
"prepublishOnly:cjs": "tsc index.ts --esModuleInterop --removeComments",
"prepublishOnly:esm": "tsc index.ts -t ES2015 --types node && mv index.js index.mjs",
"prepublishOnly": "npm run prepublishOnly:esm; npm run prepublishOnly:cjs"
},
"devDependencies": {
"typescript": "^4.0.2"
},
}
prepublishOnly:esm
renames the output manually because TypeScript can't yet generate .mjs
output directly and --outFile
doesn't work with ES Modules.
The exports
block has the "conditional exports that enable TypeScript code transpiled with ES Modules, to use named imports. TypeScript doesn't directly support .mjs input files.
No tsconfig.json
was necessary for this simple module.
Solution 3
Ivan's answer is helpful, but I also should note that that because I was using node 12.16.3, I also needed to add the --experimental-modules
flag to my start script in package.json
:
"type": "module",
"scripts": {
"start": "node --experimental-modules --experimental-json-modules server.mjs",
}
-
"type": "module"
tells node that you should use ES6 modules - file name of
.mjs
further makes it clear that we're working with a module JavaScript file -
--experimental-modules
and--experimental-json-modules
let you useimport
in node version 12.
Then I was able to do things like import express from 'express';
(where express 4.17.1 is a CommonJS module), and it worked fine.
Solution 4
Make sure the module in question has a index.js
that exports the code you want to import
or require
.
In the package.json
under the dependencies
attribute add the following:
"myCustomModule":"file:./path/to/myCustomModule"
After you have done this run npm install
.
Once that is completed look inside the node_modules
of the project root and you will see a directory named myCustonModule
.
Now in any project file you can import
or require
that code as you would any other mode_module
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Luke
Software Engineer / Web App Developer / Hobbyist Gamedev
Updated on September 15, 2022Comments
-
Luke over 1 year
I have a node app that I'd like to use in the standard ES6 module format (i.e.,
"type": "module"
in thepackage.json
, and usingimport
andexport
throughout) without transpiling down to ES5. But I would like to take advantage of some older libraries such as a express and socket.io that use CommonJS /require
format. What are my options (as of 5/2020, Node 12.16.3) for combining CommonJS modules into an ES6 app?-
Chance almost 4 yearsYou can mix and match the two? I don't think you'll have any issues.
-
-
xamgore over 3 yearsStarting from nodejs
v14.13.0
it is possible to use qualified imports of CJS modules. -
joegomain about 2 yearsHow does an index.js export code you want to import? The module in question is a commonjs module.