webpack配置不能使用ES6导入作为相对路径

Question

I have converted my Webpack configuration files from CommonJS to ES6 Modules to cjs-to-es6 . Some of the ES6 import statements such as this works:

import config from '../config'

Whilst this line does not work

import utils from './utils'

Resulting in this error

$ babel-node ./node_modules/.bin/webpack-dev-server --inline --progress --config build/webpack.dev.conf.js
/my/directory/build/vue-loader.conf.js:34
  loaders: _utils2.default.cssLoaders({
                           ^

TypeError: Cannot read property 'cssLoaders' of undefined
    at Object.<anonymous> (/my/directory/build/vue-loader.conf.js:19:18)
    at Module._compile (module.js:649:30)
    at loader (/Users/hanxue/.config/yarn/global/node_modules/babel-register/lib/node.js:144:5)
    at Object.require.extensions.(anonymous function) [as .js] (/Users/hanxue/.config/yarn/global/node_modules/babel-register/lib/node.js:154:7)
    at Module.load (module.js:561:32)
    at tryModuleLoad (module.js:501:12)
    at Function.Module._load (module.js:493:3)
    at Module.require (module.js:593:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (/my/directory/build/webpack.base.conf.js:5:1)
error An unexpected error occurred: "Command failed.

Workaround

Changing

import utils from './utils'

to

const utils = require('./utils')

will eliminate the error message.

Background

webpack: 4.0.1 node: v9.8.0 yarn: 1.5.1

Directory structure

$ ls -a config/
.       .babelrc    index.js    test.env.js
..      dev.env.js  prod.env.js
$ ls -a build/
.           check-versions.js   webpack.base.conf.js
..          logo.png        webpack.dev.conf.js
.babelrc        utils.js        webpack.prod.conf.js
build.js        vue-loader.conf.js  webpack.temp.js

Content of build/.babelrc and config/.babelrc :

{
  "presets": ["es2015"]
}

Relevant package.json content

"scripts": {
    "dev": "babel-node ./node_modules/.bin/webpack-dev-server --inline --progress --config build/webpack.dev.conf.js",
    "start": "npm run dev",
    "unit": "jest --config test/unit/jest.conf.js --coverage",
    "e2e": "node test/e2e/runner.js",
    "test": "npm run unit && npm run e2e",
    "lint": "eslint --ext .js,.vue src test/unit/specs test/e2e/specs",
    "build": "node build/build.js"
  },

Question

How can I make import utils from './utils' work correctly?

Answer 1

Replace import utils from './utils' to import * as utils from './utils' .

• import something from 'module' imports the default export as something
• import * as something from 'module' imports everything as something

It only works if utils.js is an ES6 module (which I assume), if it's a CommonJS module ( module.exports ) then both should work.

At runtime the Babel CommonJS plugin will check if the module is ES6 or CommonJS (using __esModule ) and :

• with import default from module :
  • if it's a CommonJS module : return module.exports
  • if it's an ES6 module : return export default (this is why it doesn't work for you)
• with import * as all from module :
  • if it's a CommonJS module : return module.exports
  • if it's an ES6 module : return all named exports in an object