config
    .use('cache-loader')
    .loader('cache-loader')
    .options({
      cacheDirectory,
      cacheIdentifier
    })
    .end()
    .use('babel-loader')
      .loader('babel-loader')
      .options({
        // do not pick local project babel config
        babelrc: false,
        presets: [
          require.resolve('@vue/babel-preset-app')
        ]
      })

第八行结尾 end() 处返回的便又是 config 了