vue vue-style-loader !css-loader错误

vue框架中，使用webpack打包vue项目，在执行npm run start的时候 出现如下错误：

!!vue-style-loader!css-loader?{"minimize":false,"sourceMap":false}!../../node_modules/vue-loader/lib/style-compiler/index?{"vue":true,"id":"data-v-1d57e5ea","scoped":false,"hasInlineConfig":false}!stylus-loader?{"sourceMap":false}!../../node_modules/vue-loader/lib/selector?type=styles&index=0!./a.vue in ./src/components/a.vue

To install it, you can run: npm install --save !!vue-style-loader!css-loader?{"minimize":false,"sourceMap":false}!../../node_modules/vue-loader/lib/style-compiler/index?{"vue":true,"id":"data-v-1d57e5ea","scoped":false,"hasInlineConfig":false}!stylus-loader?{"sourceMap":false}!../../node_modules/vue-loader/lib/selector?type=styles&index=0!./a.vu

解决办法：

npm install sass-loader --save-dev;
npm install node-sass --save-dev;

然后运行npm run start就可以 了