webpack4 提倡，一旦用了这个，不能使用 style-loader 以及 css module
安装
npm install –save-dev mini-css-extract-plugin
rules
rules: [
{
test: /\.css$/,
use: [{
loader: MiniCssExtractPlugin.loader,
options: {
// you can specify a publicPath here
// by default it use publicPath in webpackOptions.output
publicPath: ‘../’
}
}, “css-loader”]
}
]
plugins
new MiniCssExtractPlugin({
// Options similar to the same options in webpackOptions.output
// both options are optional
filename: _modeflag ? “styles/[name].[hash:5].css” : “styles/[name].css”,
chunkFilename: _modeflag ? “styles/[id].[hash:5].css” : “styles/[id].css”
}),