Import '.json' extension in ES6 Node.js throws an error

Question

We're trying to use the new ways of exporting and importing modules for ES6 with Node.js. It's important for us to get the version number from the package.json file. The following code should do that:

import {name, version} from '../../package.json'

However, on execution the following error is thrown:

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".json" for T:\ICP\package.json imported from T:\ICP\src\controllers\about.js

Is there something we're missing?
Is the extension .json not supported?
Is there another way to retrieve this information using Node.js 13+?

Jink

Do you have a json file in that path? Have you tried other ways to import like import pkg from ('../../package.json')? – Tarrel

Yes, the .json file location is correct. – Jink

Answer 1

From Node.js version 17.5.0 onward, importing a JSON file is possible using Import Assertions:

import packageFile from "../../package.json" assert { type: "json" };

const {
    name,
    version
  } = packageFile;

• assert { type: "json" } is mandatory
• Destructuring such as { name, version } is not possible in the import declaration directly
• The contents of the JSON file are exported as a default export, so they need to be imported from default.

The dynamic import version looks like this:

const {
    default: {
      name,
      version
    }
  } = await import("../../package.json", {
    assert: {
      type: "json"
    }
  });

Since import assertions and JSON modules have only recently promoted to stage 3, older versions of Node.js might have supported an older syntax. According to the compatibility tables on MDN for import declarations and dynamic import, older versions of Node.js (16.0.0 – 16.14.0 and 17.0.0 – 17.4.0) had varying support:

• These versions required the --experimental-json-modules flag:

  node --experimental-json-modules about.js
  

• Some versions did not support import assertions on dynamic import

• Some versions did not support the "json" type, specifically

• Some versions relied on an older proposal which did not specify the assert syntax yet

Perdita

Hii Idder, Even I got the same error after adding the flag . yarn run dev --experimental-json-modules that's the script is used to run my project – Loveinidleness

But it's annoying to add that flag every time. Can it be set permanently? – Companionate

@Companionate You can add the flag to one of your startup scripts in package.json. – Extranuclear

Answer 2

You can sill import require in an ES6 module for Node.js:

import { createRequire } from "module"; // Bring in the ability to create the 'require' method
const require = createRequire(import.meta.url); // construct the require method
const my_json_file = require("path/to/json/your-json-file.json") // use the require method

Pym

Node.Js v15 lastest give me this error ReferenceError: require is not defined – Translate

@CAlonsoCOrtega We are creating the require on line 2 of my answer. If it is undefined, you must have skipped the first few lines. – Pym

Answer 3

You can use it as in docs node-js as follow:

import { readFile } from 'fs/promises';

const json = JSON.parse(await readFile(new URL('../../package.json', import.meta.url)));

Edwin

If you're doing this on a server... I highly recommend the cleaner fs-extra, which promises everything transparently and supports recursive directory copy – Marquetry

eslint throws error on this as the await keyword can only be used within async functions – Amaliaamalie

Answer 4

2022

From Node.js v16 & v18 official documentation:

import SomeJson from './some.json' assert { type: 'json' }

And run it with the matching experimental flag:

node --experimental-json-modules ./your-file.js

Michellmichella

Answer 5

I had this same issue when compiling using Vite. Not even changing with to asset worked for me, I had to change the file from .json to .js and add export default at the beginning of the file to be able to import the data.

For me, this was the solution and it also simplified all the NodeJS syntax bureaucracy.

Concernment

Answer 6

try to use

process.env.npm_package_version

this might help you

Earhart

This will only work if the app is started with npm, which is not always the case. – Jink

did you try using fs to load the file ? – Earhart

That seems to be bad practice as it loads the complete file which shows the dependencies and other information that mekes the app vulnerable to attacks. – Jink

This feature will probably be removed... due to the mentioned security concerns, and the lack of support for deno and qbrt – Marquetry