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Import ‘.json’ extension in ES6 Node.js throws an error

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:ICPpackage.json imported from T:ICPsrccontrollersabout.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+?

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Answer

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

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