feat: add native .env file loading support

[shivarm]

Giving a try

This example demonstrates how to use Express's built-in environment variable loading from .env files.

Automatically loads .env, .env.[NODE_ENV], and .env.local

import express from "express";

express.loadEnv();

Enable watch mode

import express from 'express';

 
const unwatch = express.loadEnv({
  watch: true,
  onChange: (changed, loaded) => {
    console.log('Environment variables changed:', changed);
  },
  onError: (err) => {
    console.error('Error reloading .env:', err.message);
  }
});

// Cleanup on shutdown
process.on('SIGINT', () => {
  unwatch();
  process.exit();
});

[krzysdz]

Modern Node.js versions support loading .env files:

• --env-file flag since v20.6.0,
• --env-file-if-exists=file flag since v22.9.0 (experimental) and stabilised in v24.10.0,
• process.loadEnvFile(path) function since v20.12.0/v21.7.0 (experimental) and stabilised in v24.10.0,
• util.parseEnv(content) function returning parsed env variables from string as an object.

I'm not sure Express should do something that can be easily done using standard Node.js functionality and that isn't really connected to serving things over HTTP.

[shivarm]

I understand the concern about scope, and I agree Express should stay focused on HTTP. However, I believe this feature complements Express's developer experience. it can watch the realtime changes in .env files, for more info you can run the example project locally and by default watch mode code is commented in example but you can read about it.

[bjohansebas]

I think this shouldn’t be handled by Express, as already mentioned, Node.js already does this, and since Express is minimalistic, I don’t think things like this should be added.