Estaba tratando de correrwebpack-4 primera vez

webpack ./src/js/app.js ./dist/app.bundle.js

muestra advertencia / error:

WARNING in configuration
The 'mode' option has not been set, webpack will fallback to 'production' for this 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 ./src/js/app.js ./dist/app.bundle.js
Module not found: Error: Can't resolve './dist/app.bundle.js' in 'D:\wamp64\www\webpack-4'
 @ multi ./src/js/app.js ./dist/app.bundle.js

Entonces traté de cambiar el modo

webpack --mode development

muestra :

ERROR in Entry module not found: Error: Can't resolve './src'