javascript - 通过 DefinePlugin 使用 Webpack 传递 NODE_ENV 值

Question

我正在尝试通过 DefinePlugin 使用 webpack 将 NODE_ENV 值注入(inject)我的代码。我或多或少地检查了一个 identical question ，但仍然无法正常工作。

具体来说，这是我的设置。

在package.json中:

"scripts": {
    "build": "rimraf dist && cross-env NODE_ENV=production webpack",
    "dev": "cross-env NODE_ENV=development && node webpack-dev-server.js"
},

在 webpack.config.js 中:

"use strict";

/* requiring the modules */
const webpack = require("webpack");
const path = require("path");

/* defining the source and distribution paths */
const DIST_DIR = path.resolve(__dirname, "dist");
const SRC_DIR = path.resolve(__dirname, "src");

const DEVELOPMENT = process.env.NODE_ENV === "development";
const PRODUCTION = process.env.NODE_ENV === "production";
// const PRODUCTION = !!process.argv.find((element) => element === '--production');
// const DEVELOPMENT = !!process.argv.find((element) => element === '--development');


/* defining the entries*/
const productionEntries = {
    home: SRC_DIR + "/_home.js",
    about: SRC_DIR + "/_about.js",
};
const developmentEntries = Object.assign({}, productionEntries, {webpackDevServer: ["webpack/hot/dev-server", "webpack-dev-server/client?http://localhost:8080"]});
const entries = PRODUCTION ? productionEntries : developmentEntries;


/* defining the output */
const output = {
    filename: "[name].js",
    path: DIST_DIR,
    publicPath: "/dist/",
    pathinfo: true,
    library: "MyLibraryName"
};


/* defining the plugins */
const plugins = PRODUCTION
    ? [
        new webpack.optimize.OccurrenceOrderPlugin(),
        new webpack.optimize.AggressiveMergingPlugin(),
        new webpack.optimize.UglifyJsPlugin({comments: false}),
    ]
    :  [
        new webpack.HotModuleReplacementPlugin(),
    ];

plugins.push(
    new webpack.optimize.CommonsChunkPlugin({name: "vendor.bundle", minChunks: 2}),
    new webpack.DefinePlugin({
        PRODUCTION: PRODUCTION,
        DEVELOPMENT: DEVELOPMENT,
    })
);


/* defining the modules -> rules -> loaders */
const modules = {
    rules:
        [
            {
                test: /\.(js|jsx)$/,
                include: SRC_DIR,
                exclude: /node_modules/,
                loader: "babel-loader",
                options:
                    {
                        presets: ["react", ["es2015", {modules: false}], "stage-2"]
                    }
            }
        ]
};



/* building the webpack config object */
const config = {
    entry: entries,
    output: output,
    module: modules,
    plugins: plugins,
    devtool: "source-map",
    target: "web",
    stats: "verbose"
};

/* exporting the webpack config */
module.exports = config;

最后，在 _about.js 我有以下内容:

// output after using: npm run dev
console.log(process.env.NODE_ENV); // prints undefined
console.log(PRODUCTION); // prints false
console.log(DEVELOPMENT); // prints false

if (module.hot) {
    module.hot.accept();
}

问题:

• 由于 npm run dev 运行成功(即服务器启动并且插件和条目被充分选择)，我不明白为什么 console.log(DEVELOPMENT) 的输出 是 false，为什么 console.log(process.env.NODE_ENV) 会打印 undefined。
• 在 webpack.config.js 内部执行的条件检查中，NODE_ENV 值被正确选择，否则插件、条目和开发服务器将不会不工作。但是，我无法使用 DefinePlugin 将该值传递给 _about.js。
• 我也试过EnvironmentPlugin，结果一样。

我的问题:请您帮我了解哪里出了问题？

---

编辑 1:

我在没有任何改进的情况下尝试了以下方法:

new webpack.DefinePlugin({
    PRODUCTION: JSON.stringify(PRODUCTION),
    DEVELOPMENT: JSON.stringify(DEVELOPMENT)
})

我在 Windows 10 上运行 node.js。

---

编辑 2:

试过了:

const DEVELOPMENT = process.env.NODE_ENV === "development";
const PRODUCTION = process.env.NODE_ENV === "production";

// with this inside plugins:
new webpack.DefinePlugin({
    "process.env.PRODUCTION": JSON.stringify(PRODUCTION),
    "process.env.DEVELOPMENT": JSON.stringify(DEVELOPMENT)
})

并且(使用 npm run dev)我得到以下输出:

console.log(process.env.PRODUCTION); // false
console.log(process.env.DEVELOPMENT); // false
console.log(process.env.NODE_ENV); // undefined
console.log(PRODUCTION); // Uncaught ReferenceError: PRODUCTION is not defined
console.log(DEVELOPMENT); // Uncaught ReferenceError: DEVELOPMENT is not defined

很遗憾，没有改进。

---

编辑 3:

我的 devDependencies 是:

"devDependencies": {
    "babel-core": "^6.21.0",
    "babel-loader": "^6.2.10",
    "babel-preset-es2015": "^6.18.0",
    "babel-preset-react": "^6.16.0",
    "babel-preset-stage-2": "^6.18.0",
    "cross-env": "^3.1.4",
    "rimraf": "^2.5.4",
    "webpack": "^2.2.0-rc.4",
    "webpack-dev-server": "^2.2.0-rc.0"
}

---

编辑 4:(已解决)

@Cleiton 发现了这个问题。这与使用 cross-env 构建 npm 脚本的方式有关。请参阅下面的完整答案。

Answer 1

问题是因为您以错误的方式使用 cross-env。它只会更改其上下文的 env 变量，因此当您使用 '&&' 运行 webpack 时，它已经消失了，webpack 什么也看不到。

所以你必须写

"scripts": {
    "build": "rimraf dist && cross-env NODE_ENV=production webpack",
    "dev": "cross-env NODE_ENV=development node webpack-dev-server.js"
},

请注意，您已经为“构建”脚本编写了正确的代码。

另一个问题是如果你想在你的代码库中引用“process.env.PRODUCTION”，你应该写:

   new webpack.DefinePlugin({
        "process.env.PRODUCTION": JSON.stringify(PRODUCTION),
        "proccess.env.DEVELOPMENT": JSON.stringify(DEVELOPMENT),
    });