code: function generateLoaders (loaders) {
      const sourceLoader = loaders.map(function (loader) {
        let extraParamChar
        if (/\?/.test(loader)) {
          loader = loader.replace(/\?/, '-loader?')
          extraParamChar = '&'
        } else {
          loader = loader + '-loader'
          extraParamChar = '?'
        }
        return loader + (options.sourceMap ? extraParamChar + 'sourceMap' : '')
      }).join('!')
  
      // Extract CSS when that option is specified
      // (which is the case during production build)
      if (options.extract) {
        return ExtractTextPlugin.extract({
          use: sourceLoader,
          fallback: 'vue-style-loader'
        })
      } else {
        return ['vue-style-loader', sourceLoader].join('!')
      }
    }
docs: generate loader string to be used with extract text plugin