index.js

const fs = require('fs');
const dotenv = require('dotenv');
const { RawSource } = require('webpack-sources');

class DotenvToExportsPlugin {
	constructor (config = {}) {
		this.config = {
			filename: './env.js',
			...config
		}
	}

	apply (compiler) {
		const pluginName = this.constructor.name;
		const { env, filter, transformKey, transformValue } = this.config;
		compiler.hooks.thisCompilation.tap(pluginName, (compilation) => {
			const defaultsFile = dotenv.parse(fs.readFileSync('./.env'));
			let envFile = {}
			if (env) {
				try {
					envFile = dotenv.parse(fs.readFileSync(`./.env.${env}`));
				} catch (e) {
					console.log('No config file for env:', env);
				}
			}
			const combinedFile = {
				...defaultsFile,
				...envFile
			};
			const activeKeys = [];
			// format to exports
			let exportFile = "";
			for (let key in combinedFile) {
				let val = combinedFile[key];
				if (filter && !filter({ key, val })) {
					continue;
				}
				if (transformKey) {
					key = transformKey({ key, val });
				}
				if (transformValue) {
					val = transformValue({ key, val });
				}
				activeKeys.push(key);
				exportFile += `const ${key} = "${val}";\n`;
			}
			exportFile += `\nexport { ${activeKeys.join(', ')} }`;
			compilation.emitAsset(this.config.filename, new RawSource(exportFile));
		});
	}
}

module.exports = DotenvToExportsPlugin;