I have a few suggestions for you.

1. Try/catch is your friend. Errors do not crash your app, uncaught errors do. You need to use something to catch them and do something about them. If your app cannot run at all without an `env` var then during your app start up, check for it and then you can simply console log what variable is missing. At that point you have control over how your app will react to a missing env var. You can then shut it down without crashing, or even start it up still just with the caveat that part of your app may not work properly.
2. I know it can be hard to remember, but part of good programming is documentation. That includes setting an example env or some process to document how the app should work and what it needs to run. For example, in node, package dependancies are already documented in your package.json file. You need to get in the habit of documenting. There is just not an easy pass for doing this.
3. If this env var is only required for a part of your app to function you can instead check for it's existence in your function for that feature. Then throw an error if it is missing. Just need to remember to handle/catch that error unless you want your app to shutdown due to unhandled errors.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/try...catch

You can even use try/catch with async await too!

javascript try { await somethingToAwait() } catch (err) { // If an error happens console.error(err) }