webpack里set NODE_ENV=production，react依然有warning？

系统是windows，想用 webpack 打包 react 生产环境代码，package.json部分代码如下：

"scripts": {
    "start": "node server.js",
    "build": "set NODE_ENV=production && webpack -p --progress --profile --colors"
  },

命令行敲入npm run build后刷新网页，为什么console里依然有warning？

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什么warning？

参考：undefined is not an object (evaluating 'process.env.NODE_ENV')

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Note: by default, React will be in development mode. To use React in production mode, set the environment variable NODE_ENV to production (using envify or webpack's DefinePlugin). A minifier that performs dead-code elimination such as UglifyJS is recommended to completely remove the extra code present in development mode.

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