Best practice when using an API key in Node.js

I have an API key I'm using in my Node.js application. Currently, I keep it stored in a text file and put it in a global variable when my application starts up.

Sooo basically it's just:

var key = getKey();
useKeyGetData(key);

I don't like having this global variable, and it's a pain to pass between files. Is there a better way to get my key where/when I need it? Is there some standard for doing so?