解决方案如下:
npm install extract-text-webpack-plugin@next
安装后的版本是(package.json):
"devDependencies": { "css-loader": "^0.28.11", "extract-text-webpack-plugin": "^4.0.0-beta.0", "file-loader": "^1.1.11", "style-loader": "^0.21.0", "url-loader": "^1.0.1" }