source: frontend/node_modules/webpack/lib/EnvironmentPlugin.js

/*
        MIT License http://www.opensource.org/licenses/mit-license.php
        Authors Simen Brekken @simenbrekken, Einar Löve @einarlove
*/

"use strict";

const DefinePlugin = require("./DefinePlugin");
const WebpackError = require("./errors/WebpackError");

/** @typedef {import("./Compiler")} Compiler */
/** @typedef {import("./DefinePlugin").CodeValue} CodeValue */

const PLUGIN_NAME = "EnvironmentPlugin";

class EnvironmentPlugin {
        /**
         * Creates an instance of EnvironmentPlugin.
         * @param {(string | string[] | Record<string, EXPECTED_ANY>)[]} keys keys
         */
        constructor(...keys) {
                if (keys.length === 1 && Array.isArray(keys[0])) {
                        /** @type {string[]} */
                        this.keys = keys[0];
                        this.defaultValues = {};
                } else if (keys.length === 1 && keys[0] && typeof keys[0] === "object") {
                        this.keys = Object.keys(keys[0]);
                        this.defaultValues =
                                /** @type {Record<string, EXPECTED_ANY>} */
                                (keys[0]);
                } else {
                        this.keys = /** @type {string[]} */ (keys);
                        this.defaultValues = {};
                }
        }

        /**
         * Applies the plugin by registering its hooks on the compiler.
         * @param {Compiler} compiler the compiler instance
         * @returns {void}
         */
        apply(compiler) {
                const definePlugin = new DefinePlugin({});

                compiler.hooks.thisCompilation.tap(PLUGIN_NAME, (compilation) => {
                        /** @type {Record<string, CodeValue>} */
                        const definitions = {};
                        for (const key of this.keys) {
                                const value =
                                        process.env[key] !== undefined
                                                ? process.env[key]
                                                : this.defaultValues[key];

                                if (value === undefined) {
                                        const error = new WebpackError(
                                                `${PLUGIN_NAME} - ${key} environment variable is undefined.\n\n` +
                                                        "You can pass an object with default values to suppress this warning.\n" +
                                                        "See https://webpack.js.org/plugins/environment-plugin for example."
                                        );

                                        error.name = "EnvVariableNotDefinedError";
                                        compilation.errors.push(error);
                                }
                                const defValue =
                                        value === undefined ? "undefined" : JSON.stringify(value);
                                definitions[`process.env.${key}`] = defValue;
                                definitions[`import.meta.env.${key}`] = defValue;
                        }
                        definePlugin.definitions = definitions;
                });
                definePlugin.apply(compiler);
        }
}

module.exports = EnvironmentPlugin;