Minimum messages code?

Thank you.
When I receive a message in

Bangle.on("message", (type, msg) => require("xxlmessage").listener(type, msg));

and I want to show a scrolling message, I need a timeout for the redraw, and a variable holding the current scroll position.
So I can make a global variable like:

var scrollPosition=0;
var scrollTimeout;
exports.messageListener = function(type, msg) {
}

Now, when I exit this code, by calling load(), will the global variables 'scrollPosition' etc. be freed from memory?
Also, can I break things, if my global variables have names that are used in other apps or the system?
I ask, because this code is in boot.js and thus always loaded. Will 'require()' load the js file on demand? What is the variable scope? The scope of require(), or global?