Webpack buildエラー

npm run buildの実行エラーは次のとおりです.

D:\MyProjects\react_ssr_demo>npm run build

> [email protected] build D:\MyProjects\react_ssr_demo
> webpack --config build/webpack.config.js

Hash: 0b1003a436390263970e
Version: webpack 4.29.3
Time: 633ms
Built at: 2019-02-09 15:46:04
 1 asset
Entrypoint app = app.0b1003a436390263970e.js
[2] ./client/App.jsx 3 KiB {0} [not cacheable] [built] [failed] [1 error]
[3] ./client/app.js 100 bytes {0} [built]
[9] (webpack)/buildin/global.js 472 bytes {0} [built]
    + 7 hidden modules

WARNING in configuration
The 'mode' option has not been set, webpack will fallback to 'production' for th
is value. Set 'mode' option to 'development' or 'production' to enable defaults
for each environment.
You can also set it to 'none' to disable any default behavior. Learn more: https
://webpack.js.org/concepts/mode/

ERROR in ./client/App.jsx
Module build failed (from ./node_modules/[email protected]@babel-loader/lib/in
dex.js):
Error: Cannot find module '@babel/core'
 babel-loader@8 requires Babel 7.x (the package '@babel/core'). If you'd like to
 use Babel 6.x ('babel-core'), you should install 'babel-loader@7'.
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:581:15)
    at Function.Module._load (internal/modules/cjs/loader.js:507:25)
    at Module.require (internal/modules/cjs/loader.js:637:17)
    at require (D:\MyProjects\react_ssr_demo
ode_modules\[email protected].
2@v8-compile-cache\v8-compile-cache.js:159:20)
    at Object. (D:\MyProjects\react_ssr_demo
ode_modules\_babel-load
[email protected]@babel-loader\lib\index.js:10:11)
    at Module._compile (D:\MyProjects\react_ssr_demo
ode_modules\_v8-compile-ca
[email protected]@v8-compile-cache\v8-compile-cache.js:178:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
    at Module.load (internal/modules/cjs/loader.js:599:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
    at Function.Module._load (internal/modules/cjs/loader.js:530:3)
    at Module.require (internal/modules/cjs/loader.js:637:17)
    at require (D:\MyProjects\react_ssr_demo
ode_modules\[email protected].
2@v8-compile-cache\v8-compile-cache.js:159:20)
    at loadLoader (D:\MyProjects\react_ssr_demo
ode_modules\[email protected].
0@loader-runner\lib\loadLoader.js:18:17)
    at iteratePitchingLoaders (D:\MyProjects\react_ssr_demo
ode_modules\_loader
[email protected]@loader-runner\lib\LoaderRunner.js:169:2)
    at runLoaders (D:\MyProjects\react_ssr_demo
ode_modules\[email protected].
0@loader-runner\lib\LoaderRunner.js:365:2)
    at NormalModule.doBuild (D:\MyProjects\react_ssr_demo
ode_modules\_webpack@
4.29.3@webpack\lib\NormalModule.js:280:3)
    at NormalModule.build (D:\MyProjects\react_ssr_demo
ode_modules\_webpack@4.
29.3@webpack\lib\NormalModule.js:427:15)
    at Compilation.buildModule (D:\MyProjects\react_ssr_demo
ode_modules\_webpa
[email protected]@webpack\lib\Compilation.js:635:10)
    at factory.create (D:\MyProjects\react_ssr_demo
ode_modules\[email protected]
@webpack\lib\Compilation.js:884:14)
    at factory (D:\MyProjects\react_ssr_demo
ode_modules\[email protected]@webpac
k\lib\NormalModuleFactory.js:405:6)
    at hooks.afterResolve.callAsync (D:\MyProjects\react_ssr_demo
ode_modules\_
[email protected]@webpack\lib\NormalModuleFactory.js:155:13)
    at AsyncSeriesWaterfallHook.eval [as callAsync] (eval at create (D:\MyProjec
ts\react_ssr_demo
ode_modules\[email protected]@tapable\lib\HookCodeFactory.js:32:
10), :6:1)
    at resolver (D:\MyProjects\react_ssr_demo
ode_modules\[email protected]@webpa
ck\lib\NormalModuleFactory.js:138:29)
    at process.nextTick (D:\MyProjects\react_ssr_demo
ode_modules\[email protected]
.3@webpack\lib\NormalModuleFactory.js:342:9)
    at process._tickCallback (internal/process/next_tick.js:61:11)
 @ ./client/app.js 2:0-27 4:16-19
npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! [email protected] build: `webpack --config build/webpack.config.js`
npm ERR! Exit status 2
npm ERR!
npm ERR! Failed at the [email protected] build script.
npm ERR! This is probably not a problem with npm. There is likely additional log
ging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     C:\Users\Administrator.PC-201812050004\AppData\Roaming
pm-cache\_l
ogs\2019-02-09T07_46_04_537Z-debug.log

この中には2つの問題がある.

WARNING in configuration

解決方法:webpack.config.jsの下にmodeを追加:‘none’module.exports = { mode: ‘none’,

ERROR in ./client/App.jsx Module build failed (from ./node_modules/[email protected]@babel-loader/lib/in dex.js):

Error: Cannot find module '@babel/core' babel-loader@8 requires Babel 7.x (the package '@babel/core'). If you'd like to use Babel 6.x ('babel-core'), you should install 'babel-loader@7'.
解決策:npm i babel-loader@7 -D