webpack配置css单独分离打包

https://www.imooc.com/video/16409   学习视频，老师的版本和目前版本不一致，问题已解决，如下：

.vue中的文件是和组件一起异步加载的

1   npm i extract-text-webpack-plugin    （注意版本）

2webpack.config.js配置

const path = require('path');
const isDev = process.env.NODE_ENV === 'development';
const HTMLPlugin = require('html-webpack-plugin');
const VueLoaderPlugin = require('vue-loader/lib/plugin');
const ExtractPlugin = require('extract-text-webpack-plugin'); //把非js代码打包成单独的资源文件，提高效率
const webpack = require('webpack');
const config = {
  target: 'web',
  entry: path.join(__dirname, 'src/index.js'), //__dirname 当前文件所在的目录地址
  output: {
    filename: 'bundle.js',
    path: path.join(__dirname, 'dist'),
  },
  module: {
    rules: [
      {
        test: /.vue$/,
        loader: 'vue-loader',
      },
      {
        test: /.jsx$/,
        loader: 'babel-loader',
      },
      {
        test: /.(gif|jpg|jpeg|png|svg)$/,
        use: [
          {
            loader: 'url-loader',
            options: {
              limit: 1024,
              name: '[name]-aaa.[ext]',
            },
          },
        ],
      },
    ],
  },
  plugins: [
    new webpack.DefinePlugin({
      'process.env': {
        NODE_ENV: isDev ? '"development"' : '"production"',
      },
    }),
    new VueLoaderPlugin(),
    new HTMLPlugin(),
  ],
  mode: 'development',
};
//判断开发环境和正式环境   cross-env 运行跨平台设置和用环境变量的脚本
if (isDev) {
  config.module.rules.push({
    test: /.styl/,
    use: [
      'style-loader',
      'css-loader',
      {
        loader: 'postcss-loader',
        options: {
          sourceMap: true,
        },
      },
      'stylus-loader',
    ],
  });
  config.devtool = '#cheap-module-eval-source-map';
  config.devServer = {
    port: 8000,
    host: '0.0.0.0',
    overlay: {
      errors: true,
    },
    hot: true,
    // open: true
  };
  config.plugins.push(
    new webpack.HotModuleReplacementPlugin(),
    new webpack.NoEmitOnErrorsPlugin()
  );
} else {
    //正式环境
  config.output.filename = '[name].[chunkhash:8].js';
  config.module.rules.push({
    test: /.styl/,
    use: ExtractPlugin.extract({
      fallback: 'style-loader',
      use: [
        'css-loader',
        {
          loader: 'postcss-loader',
          options: {
            sourceMap: true,
          },
        },
        'stylus-loader',
      ],
    }),
  });
//  config.plugins.push(new ExtractPlugin('styles.[contentHash:8].css'));//这里有问题偶，contentHash是关键字，不可使用

  　　config.plugins.push(new ExtractPlugin('styles.[contentHash:hex:8].css'));

}
module.exports = config;

3npm run build

"scripts": {
    "test": "echo "Error: no test specified" && exit 1",
    "build": "cross-env NODE_ENV=production webpack --config webpack.config.js","dev": "cross-env NODE_ENV=development webpack-dev-server --config webpack.config.js"
  },

4报错处理

 版本问题导致的，webpack4.0以上用3.x extract-webpack-plugin 打包会不兼容，extract-webpack-plugin升级就可以了

解决方法：npm i extract-text-webpack-plugin@4.0.0-beta.0

 是因为webpack4.3 包含了contenthash 这个关键字段，所以在ExtractPlugin 中不能使用contenthash，
使用mds:contenthash:hex:8 替代