Why not possible to use ES imports in vue.config.js file with VueJS?

Question

Why aren't ES imports working in vue.config.js file?

In example:

import * as path from 'path';
import * as pjson from './package.json';

module.exports = {
  configureWebpack: {
    resolve: {
      alias: {
        '@': path.join(__dirname, '/src'), // Alias @ to /src folder for ES/TS imports
      },
    },
  },
  pwa: {
    name: pjson.title,
    assetsVersion: pjson.version,
  },
};

Getting error after running npm run lint command (which uses vue-cli-service):

\vue.config.js:1
import * as path from 'path';

SyntaxError: Unexpected token *
    at Module._compile (internal/modules/cjs/loader.js:720:23)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:787:10)
    at Module.load (internal/modules/cjs/loader.js:643:32)
    at Function.Module._load (internal/modules/cjs/loader.js:556:12)
    at Module.require (internal/modules/cjs/loader.js:6

Also import 'path'; is not working either (tried also other syntax variants):

import 'path';
       ^^^^^^

SyntaxError: Unexpected string

The reason I'm trying to refactor from const path = require('path'); syntax is to avoid this new linter error after ESLint plugins upgrade:

Require statement not part of import statement. eslint(@typescript-eslint/no-var-requires)

But it seems I still need to append this on top of the file: /* eslint-disable @typescript-eslint/no-var-requires */

Answer 1

The file vue.config.js is loaded by @vue/cli-shared-utils/lib/module.js via CommonJS require. Because of that, it expects vue.config.js to be CommonJS, too.

There are a few schemes you could employ to overcome this built-in limitation such as using vue.config.js to

require('@babel/register'); 

then require another file like vue.config.mjs where your ESM-based code resides.

But given this is only a config file that usually doesn't have a lot of code, it may be better not to fight city hall and instead use CommonJS.