Edits by @JLHwung

The report includes a package.json and a webpack configuration, but it is an import from Babel issue 8599 and directs readers to a specific comment there. Start with that linked discussion and compare the dependency setup shown here; the payload does not define a repository change or a verifiable done condition.

Edits by @JLHwung

If you hit this issue via search engines, please refer to https://github.com/babel/babel/issues/8599#issuecomment-417880788.

Bug Report

Current Behavior
Recently I'm trying to setup babel with webpack. and I'm getting an error.

ERROR in ./src/index.js
Module build failed (from ./node_modules/babel-loader/lib/index.js):
Error: Cannot find module '@babel/core'
ERROR in ./src/index.js
Module build failed (from ./node_modules/babel-loader/lib/index.js):
Error: Cannot find module '@babel/core'
npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! webpack-4-tutorial@1.0.0 build: `webpack --mode production`
npm ERR! Exit status 2
npm ERR!
npm ERR! Failed at the webpack-4-tutorial@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:
npm ERR!     C:\Users\Mentos\AppData\Roaming\npm-cache\_logs\2018-09-01T10_50_57_222Z-debug.log

package.json

{
  "name": "webpack-4-tutorial",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "dev": "webpack --mode development",
    "build": "webpack --mode production"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "babel-core": "^6.26.3",
    "babel-loader": "^8.0.0",
    "babel-preset-env": "^1.7.0",
    "webpack": "^4.17.1",
    "webpack-cli": "^3.1.0"
  }
}

package.json

// webpack v4
const path = require('path');
module.exports = {
    entry: { main: './src/index.js' },
    output: {
        path: path.resolve(__dirname, 'dist'),
        filename: 'main.js'
    },
    module: {
        rules: [
            {
                test: /\.js$/,
                exclude: /node_modules/,
                use: {
                    loader: "babel-loader"
                }
            }
        ]
    }
};

Expected behavior/code
Babel Configuration (.babelrc, package.json, cli command)

{
    "presets": [
        "env"
    ]
}

debug.log

0 info it worked if it ends with ok
1 verbose cli [ 'C:\\Program Files\\nodejs\\node.exe',
1 verbose cli   'C:\\Program Files\\nodejs\\node_modules\\npm\\bin\\npm-cli.js',
1 verbose cli   'run',
1 verbose cli   'build' ]
2 info using npm@6.2.0
3 info using node@v10.9.0
4 verbose run-script [ 'prebuild', 'build', 'postbuild' ]
5 info lifecycle webpack-4-tutorial@1.0.0~prebuild: webpack-4-tutorial@1.0.0
6 info lifecycle webpack-4-tutorial@1.0.0~build: webpack-4-tutorial@1.0.0
7 verbose lifecycle webpack-4-tutorial@1.0.0~build: unsafe-perm in lifecycle true
8 verbose lifecycle webpack-4-tutorial@1.0.0~build: PATH: C:\Program Files\nodejs\node_modules\npm\node_modules\npm-lifecycle\node-gyp-bin;D:\Playground\webpack-4-tutorial\node_modules\.bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Windows\System32\OpenSSH\;C:\Program Files (x86)\AMD\ATI.ACE\Core-Static;C:\Program Files\Git\cmd;C:\Program Files\TortoiseGit\bin;C:\Program Files\Microsoft VS Code\bin;C:\Program Files\nodejs\;C:\Users\Mentos\AppData\Local\Microsoft\WindowsApps;;C:\Program Files\Microsoft VS Code\bin;C:\Users\Mentos\AppData\Local\Programs\Microsoft VS Code\bin;C:\Users\Mentos\AppData\Roaming\npm
9 verbose lifecycle webpack-4-tutorial@1.0.0~build: CWD: D:\Playground\webpack-4-tutorial
10 silly lifecycle webpack-4-tutorial@1.0.0~build: Args: [ '/d /s /c', 'webpack --mode production' ]
11 silly lifecycle webpack-4-tutorial@1.0.0~build: Returned: code: 2  signal: null
12 info lifecycle webpack-4-tutorial@1.0.0~build: Failed to exec build script
13 verbose stack Error: webpack-4-tutorial@1.0.0 build: `webpack --mode production`
13 verbose stack Exit status 2
13 verbose stack     at EventEmitter.<anonymous> (C:\Program Files\nodejs\node_modules\npm\node_modules\npm-lifecycle\index.js:304:16)
13 verbose stack     at EventEmitter.emit (events.js:182:13)
13 verbose stack     at ChildProcess.<anonymous> (C:\Program Files\nodejs\node_modules\npm\node_modules\npm-lifecycle\lib\spawn.js:55:14)
13 verbose stack     at ChildProcess.emit (events.js:182:13)
13 verbose stack     at maybeClose (internal/child_process.js:961:16)
13 verbose stack     at Process.ChildProcess._handle.onexit (internal/child_process.js:250:5)
14 verbose pkgid webpack-4-tutorial@1.0.0
15 verbose cwd D:\Playground\webpack-4-tutorial
16 verbose Windows_NT 10.0.17134
17 verbose argv "C:\\Program Files\\nodejs\\node.exe" "C:\\Program Files\\nodejs\\node_modules\\npm\\bin\\npm-cli.js" "run" "build"
18 verbose node v10.9.0
19 verbose npm  v6.2.0
20 error code ELIFECYCLE
21 error errno 2
22 error webpack-4-tutorial@1.0.0 build: `webpack --mode production`
22 error Exit status 2
23 error Failed at the webpack-4-tutorial@1.0.0 build script.
23 error This is probably not a problem with npm. There is likely additional logging output above.
24 verbose exit [ 2, true ]

Environment

• Babel version(s): 6.26.3
• Node/npm version: Node 10.9.0/npm 6.2]
• OS: Windows 10
• How you are using Babel:loader

Possible Solution

Additional context/Screenshots
I follow the same step in past and it was work fine.

Originally posted by @palak-temp in https://github.com/babel/babel/issues/8599