What’s the best way to manage environment variables in Node.js projects?

I've run into a common issue where my process.env variables ended up being undefined because my configuration files were loaded before dotenv had a chance to initialize. To address this, I set up separate files for development and production environments: .env.development and .env.production. I dynamically load these based on the NODE_ENV value and then import the appropriate configuration.

Here's a snippet of my code:
```js
import dotenv from "dotenv";
const ENV = (process.env.NODE_ENV || "development").trim().toLowerCase();
dotenv.config({ path: `.env.${ENV}` });

let config;
if (ENV === "production") {
const prod = await import("./production.js");
config = prod.default;
} else {
const dev = await import("./development.js");
config = dev.default;
}
export default config;
```

With this setup:
- If NODE_ENV is set to development, it connects to a local MongoDB.
- If NODE_ENV is set to production, it connects to an Atlas cluster.

This approach works well for me, but I'm curious to know how others handle their environment variables and configurations in their projects. Do you guys use a single .env file with conditionals, rely on libraries like config or dotenv-flow, or do you have a different method like using Docker secrets or cloud service configurations? Looking forward to hearing what works for you!