报错

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/configuration/mode/

解决：

在package.json文件里进行修改：增加如下：

scripts": {

   "dev": "webpack-dev-server --mode development",

   "build": "webpack --mode development"