Core-js is not installed
In the directory where package.json is located: npm i core-js -D

ERROR in . /src/js/index.js 1:0-48
Production environment configuration \15js compatibility handling\src\js'

ERROR in ./src/js/index.js 2:0-39
Module not found: Error: Can't resolve 'core-js/modules/es.promise.js' in 'D:\Desktop\My Files\RecentlyStudy\WebPack\demo\3.webpack production environment configuration 
webpack production environment configuration \15js compatibility handling\src\js'

ERROR in ./src/js/index.js 3:0-39
Module not found: Error: Can't resolve 'core-js/modules/web.timers.js' in 'D:\Desktop\My Files\RecentlyStudy\WebPack\demo\3.webpack

3 errors have detailed information that is not shown.
Use 'stats.errorDetails: true' resp. '--stats-error-details' to show it.