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Question

所以我刚刚开始学习webpack（2.2.1）并做出反应，我遇到了NODE_ENV的一些问题。我在package.json中设置它是这样的：

 "scripts": {
    "start": "set NODE_ENV=production&& webpack",
    "test": "echo \"Error: no test specified\" && exit 1"
 }

然后我将一个console.log(process.env.NODE_ENV)放入webpack的入口文件中，看看它是否已设置并按预期进行。 但是，当我在项目的根目录中名为server.js的文件中运行express时：

const express = require('express');
const path = require('path');
const app = new express;
console.log(process.env.NODE_ENV);

const port = process.env.PORT || 3000;
app.use(express.static('public'));

app.get('/',(req,res)=>{
    res.sendFile(path.join(__dirname, "public/index.html"));
});
app.listen(port, ()=>{
    console.log("listening...", process.env.NODE_ENV);
});

process.env.NODE_ENV未定义。
这是webpack.config

const webpack = require('webpack');
const path = require('path');
const ExtractTextPlugin = require('extract-text-webpack-plugin');
const VENDOR_LIBS = ['react', 'react-dom', 'bootstrap', 'jquery'];

module.exports = {
    entry: {
        bundle: './src/index.js',
        vendor: VENDOR_LIBS
    },
    output: {
        path: __dirname + '/public',
        filename: '[name].js'
    },
    module: {
        rules: [
            {
                use: 'babel-loader',
                test: /\.(js|jsx)$/,
                exclude: /node_modules/
            },
            {
            loader: ['style-loader', 'css-loader'],
            test: /.css$/
            },
            {
            test: /\.ttf(\?v=\d+\.\d+\.\d+)?$/,
            loader: 'url?limit=10000&mimetype=application/octet-stream'
            },
            {
            loader: 'url?limit=10000!img?progressive=true',
            test:  /\.(jpe?g|png|gif|svg)$/i
            }
        ]
    },

    plugins: [
        new webpack.ProvidePlugin({
            $: 'jquery',
            jquery: 'jquery',
            jQuery: 'jquery'
        }),
        new webpack.optimize.CommonsChunkPlugin({name: "vendor", filename: "vendor.js"}),
        new ExtractTextPlugin("./styles/bootstrap.css"),
        new webpack.DefinePlugin({'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV)})
    ]
}

非常感谢任何帮助。