Nest.js: check if all used environment variables are defined in .env before building.

check_env.ts

import { createReadStream } from 'node:fs';
import { readdir } from 'node:fs/promises';
import { resolve } from 'node:path';

let envFileContent = '';
createReadStream('.env')
    .on('data', (chunk) => {
        envFileContent += chunk.toString();
    })
    .on('end', () => {
        checkEnv(envFileContent.split('\n').filter((l) => l !== ''));
    });

async function* getFiles(dir: string): AsyncGenerator<string> {
    const dirents = await readdir(dir, { withFileTypes: true });
    for (const dirent of dirents) {
        const file = resolve(dir, dirent.name);
        if (dirent.isDirectory()) yield* getFiles(file);
        else yield file;
    }
}

async function checkEnv(envArr: string[]) {
    for await (const file of getFiles('./src')) {
        let content = '';
        createReadStream(file)
            .on('data', (chunk) => {
                content += chunk.toString();
            })
            .on('end', () => {
                const arr = content.split('\n');
                for (const line of arr) {
                    const match = line.match(
                        /configService\.get.*\((\S*(?:'|"))(?:\)|,\s)?((\S*(?:'|")))/
                    );
                    if (!match) continue;
                    const envKey = match[1].replaceAll(/'|"/g, '');
                    const defaultValue = match[3]?.replaceAll(/'|"/g, '');
                    const foundEnv = envArr.find((env) => env.startsWith(envKey));
                    if (!foundEnv || envKey + '=' === foundEnv)
                        throw new Error(
                            `A used process.env.${envKey} is not defined in the '.env' file. ${
                                defaultValue ? `defaultValue: ${defaultValue}` : ''
                            }`
                        );
                }
            });
    }
}

"scripts": {
    "prebuild": "rimraf dist",
}

to

"scripts": {
    "prebuild": "npx ts-node check_env.ts && rimraf dist",
}