The 'mode' option has not been set, webpack will fallback to 'production' for th is value

1、错误描述

C:\Users\Administrator>cd cma

C:\Users\Administrator\cma>webpack you.js today.js
Hash: 39919aae8cb041a7549f
Version: webpack 4.10.2
Time: 588ms
Built at: 2018-06-01 21:01:06
 1 asset
Entrypoint main = main.js
[0] ./you.js 288 bytes {0} [built]
[1] multi ./you.js today.js 40 bytes {0} [built]

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 multi ./you.js today.js
Module not found: Error: Can't resolve 'today.js' in 'C:\Users\Administrator\cma
'
 @ multi ./you.js today.js

C:\Users\Administrator\cma>webpack you.js today.js
Hash: 2ffa3d7e0a8a6e808dda
Version: webpack 4.10.2
Time: 613ms
Built at: 2018-06-01 21:11:11
  Asset     Size  Chunks             Chunk Names
main.js  1.1 KiB       0  [emitted]  main
Entrypoint main = main.js
[0] ./today.js 0 bytes {0} [built]
[1] ./you.js 288 bytes {0} [built]
[2] multi ./you.js ./today.js 40 bytes {0} [built]

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/

C:\Users\Administrator\cma>webpack you.js today.js
Hash: 2ffa3d7e0a8a6e808dda
Version: webpack 4.10.2
Time: 156ms
Built at: 2018-06-01 21:13:04
  Asset     Size  Chunks             Chunk Names
main.js  1.1 KiB       0  [emitted]  main
Entrypoint main = main.js
[0] ./today.js 0 bytes {0} [built]
[1] ./you.js 288 bytes {0} [built]
[2] multi ./you.js ./today.js 40 bytes {0} [built]

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/

C:\Users\Administrator\cma>

2、错误原因

     没有设置webpack的模式，是生产还是开发（production or development）

3、解决办法

     执行命令：webpack --mode=production或者webpack --mode=development

C:\Users\Administrator>webpack --mode=production
Hash: 68029a5423f50b49c81f
Version: webpack 4.10.2
Time: 91ms
Built at: 2018-06-01 21:18:40

ERROR in Entry module not found: Error: Can't resolve './src' in 'C:\Users\Admin
istrator'

C:\Users\Administrator>