title: Webpack + Babel: ERROR in ./_assets/js/src/main.js Module not found
body: <p>I am generally having problems with webpack. But in this case, the console tells me, that webpack can't find the core-js modules. In the warning at the top it says "we recommend explicitly setting the core-js version you are using via the <code>corejs</code> option". But how can I specify a core-js version? I couldn't find any hints in other webpack/babel related questions or in the official documentations.</p>
  
  <p><strong>Console output</strong></p>
  
  <pre><code> $ npm run build
  
      &gt; jkk-onepager@1.0.0 build /Users/frankwenzel/Repositories/_GitLab/jkk-onepager
      &gt; webpack
  
  
      WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
  
      You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
  
        npm install --save core-js@2    npm install --save core-js@3
        yarn add core-js@2              yarn add core-js@3
  
      @babel/preset-env: `DEBUG` option
  
      Using targets:
      {
        "android": "4",
        "chrome": "29",
        "edge": "15",
        "firefox": "52",
        "ie": "11",
        "ios": "7",
        "opera": "57",
        "safari": "9",
        "samsung": "4"
      }
  
      Using modules transform: auto
  
      Using plugins:
        transform-template-literals { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9" }
        transform-literals { "android":"4", "chrome":"29", "firefox":"52", "ie":"11", "ios":"7" }
        transform-function-name { "android":"4", "chrome":"29", "edge":"15", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-arrow-functions { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-block-scoped-functions { "android":"4", "chrome":"29", "ios":"7", "safari":"9" }
        transform-classes { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-object-super { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-shorthand-properties { "android":"4", "chrome":"29", "ie":"11", "ios":"7" }
        transform-duplicate-keys { "android":"4", "chrome":"29", "ie":"11", "ios":"7" }
        transform-computed-properties { "android":"4", "chrome":"29", "ie":"11", "ios":"7" }
        transform-for-of { "android":"4", "chrome":"29", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-sticky-regex { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-dotall-regex { "android":"4", "chrome":"29", "edge":"15", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-unicode-regex { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-spread { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-parameters { "android":"4", "chrome":"29", "edge":"15", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-destructuring { "android":"4", "chrome":"29", "edge":"15", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-block-scoping { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-typeof-symbol { "android":"4", "chrome":"29", "ie":"11", "ios":"7" }
        transform-new-target { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-regenerator { "android":"4", "chrome":"29", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-exponentiation-operator { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-async-to-generator { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        proposal-async-generator-functions { "android":"4", "chrome":"29", "edge":"15", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        proposal-object-rest-spread { "android":"4", "chrome":"29", "edge":"15", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        proposal-unicode-property-regex { "android":"4", "chrome":"29", "edge":"15", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        proposal-json-strings { "android":"4", "chrome":"29", "edge":"15", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        proposal-optional-catch-binding { "android":"4", "chrome":"29", "edge":"15", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        transform-named-capturing-groups-regex { "android":"4", "chrome":"29", "edge":"15", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
  
      Using polyfills with `entry` option:
  
      [/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src/main.js] Replaced @babel/polyfill entries with the following polyfills:
        es6.array.copy-within { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "samsung":"4" }
        es6.array.fill { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "samsung":"4" }
        es6.array.find { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "samsung":"4" }
        es6.array.find-index { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "samsung":"4" }
        es7.array.flat-map { "android":"4", "chrome":"29", "edge":"15", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        es6.array.from { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        es7.array.includes { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        es6.array.iterator { "android":"4", "chrome":"29", "ie":"11", "ios":"7" }
        es6.array.of { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "samsung":"4" }
        es6.array.sort { "android":"4", "chrome":"29", "ios":"7", "safari":"9", "samsung":"4" }
        es6.array.species { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        es6.date.to-json { "ios":"7", "safari":"9" }
        es6.date.to-primitive { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        es6.function.has-instance { "android":"4", "chrome":"29", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
        es6.function.name { "ie":"11" }
        es6.map { "android":"4", "chrome":"29", "firefox":"52", "ie":"11", "ios":"7", "safari":"9", "samsung":"4" }
  
      Hash: 6c65e92d03f5b74daa97
      Version: webpack 4.29.6
      Time: 2613ms
      Built at: 2019-04-01 14:03:40
          Asset     Size  Chunks             Chunk Names
      bundle.js  118 KiB     app  [emitted]  app
      Entrypoint app = bundle.js
      [./_assets/js/src/main.js] 24.3 KiB {app} [built]
          + 48 hidden modules
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.array.copy-within' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 1:0-47
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.array.fill' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 2:0-40
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.array.find' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 3:0-40
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.array.find-index' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 4:0-46
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.array.from' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 6:0-40
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.array.iterator' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 8:0-44
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.array.of' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 9:0-38
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.array.sort' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 10:0-40
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.array.species' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 11:0-43
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.date.to-json' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 12:0-42
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.date.to-primitive' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 13:0-47
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.function.has-instance' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 14:0-51
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.function.name' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 15:0-43
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.map' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 16:0-33
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.math.acosh' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 17:0-40
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.math.asinh' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 18:0-40
  
      ERROR in ./_assets/js/src/main.js
      Module not found: Error: Can't resolve 'core-js/modules/es6.math.atanh' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
       @ ./_assets/js/src/main.js 19:0-40
  
  
       @ ./_assets/js/src/main.js 129:0-42
      npm ERR! code ELIFECYCLE
      npm ERR! errno 2
      npm ERR! jkk-onepager@1.0.0 build: `webpack`
      npm ERR! Exit status 2
      npm ERR! 
      npm ERR! Failed at the jkk-onepager@1.0.0 build script.
      npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
  
      npm ERR! A complete log of this run can be found in:
  </code></pre>
  
  <p><strong>package.json</strong></p>
  
  <pre><code>{
    "name": "jkk-onepager",
    "version": "1.0.0",
    "description": "",
    "main": "index.js",
    "scripts": {
      "test": "echo \"Error: no test specified\" &amp;&amp; exit 1",
      "build": "webpack",
      "start": "webpack-dev-server"
    },
    "repository": {
      "type": "git",
      "url": "http://10.8.1.1:850/root/jkk-onepager.git"
    },
    "author": "",
    "license": "ISC",
    "dependencies": {
      "@babel/core": "^7.4.0",
      "@babel/polyfill": "^7.4.0",
      "@babel/preset-env": "^7.4.2",
      "babel-loader": "^8.0.5",
      "babel-plugin-syntax-flow": "^6.18.0",
      "babel-plugin-transform-class-properties": "^6.24.1",
      "babel-plugin-transform-decorators-legacy": "^1.3.5",
      "babel-plugin-transform-flow-strip-types": "^6.22.0",
      "babel-plugin-transform-object-rest-spread": "^6.26.0",
      "babel-polyfill": "^6.26.0",
      "babel-preset-es2015": "^6.24.1",
      "core-js": "^3.0.0",
      "webpack-dev-server": "^3.2.1"
    },
    "devDependencies": {
      "babel-core": "^7.0.0-bridge.0",
      "babel-preset-env": "^1.7.0",
      "webpack": "^4.29.6",
      "webpack-cli": "^3.3.0"
    }
  }
  </code></pre>
  
  <p><strong>.babelrc</strong></p>
  
  <pre><code>{
      "presets": [
          ["@babel/preset-env", {
              "useBuiltIns": "entry",
              "debug": true
          }]
      ]
  }
  </code></pre>
  
  <p>Edit:</p>
  
  <p>After some additional research I found this and tried it:</p>
  
  <pre><code>webpack --progress --color --watch --display-error-details
  
  ERROR in ./_assets/js/src/main.js
  Module not found: Error: Can't resolve 'core-js/modules/web.dom.iterable' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
  resolve 'core-js/modules/web.dom.iterable' in '/Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src'
    Parsed request is a module
    using description file: /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/package.json (relative path: ./_assets/js/src)
      Field 'browser' doesn't contain a valid alias configuration
      resolve as module
        /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/src/node_modules doesn't exist or is not a directory
        /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/js/node_modules doesn't exist or is not a directory
        /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/_assets/node_modules doesn't exist or is not a directory
        /Users/frankwenzel/Repositories/_GitLab/node_modules doesn't exist or is not a directory
        /Users/frankwenzel/Repositories/node_modules doesn't exist or is not a directory
        /Users/frankwenzel/node_modules doesn't exist or is not a directory
        /Users/node_modules doesn't exist or is not a directory
        /node_modules doesn't exist or is not a directory
        looking for modules in /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/node_modules
          using description file: /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/package.json (relative path: ./node_modules)
            Field 'browser' doesn't contain a valid alias configuration
            using description file: /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/node_modules/core-js/package.json (relative path: ./modules/web.dom.iterable)
              no extension
                Field 'browser' doesn't contain a valid alias configuration
                /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/node_modules/core-js/modules/web.dom.iterable doesn't exist
              .wasm
                Field 'browser' doesn't contain a valid alias configuration
                /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/node_modules/core-js/modules/web.dom.iterable.wasm doesn't exist
              .mjs
                Field 'browser' doesn't contain a valid alias configuration
                /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/node_modules/core-js/modules/web.dom.iterable.mjs doesn't exist
              .js
                Field 'browser' doesn't contain a valid alias configuration
                /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/node_modules/core-js/modules/web.dom.iterable.js doesn't exist
              .json
                Field 'browser' doesn't contain a valid alias configuration
                /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/node_modules/core-js/modules/web.dom.iterable.json doesn't exist
              as directory
                /Users/frankwenzel/Repositories/_GitLab/jkk-onepager/node_modules/core-js/modules/web.dom.iterable doesn't exist
  </code></pre>