How to call Nunjucks configuration file into my main app.js - express

Question

Within my Express 4.17.1 app, I have the following template setup (below). I have read sources on pulling out routes into their own module files. But how can I take my nunjucks configuration code below and have it called into my app.js as a separate file and still use my template filters? Just trying to unclutter.
Thanks!
App.js
const express = require('express');
const nunjucks = require('nunjucks');
const env = new nunjucks.Environment();
const path = require('path');
//...other stuff...
// VIEWS | NUNJUCKS
app.set('view engine', 'njk');
app.set('views', [path.join(__dirname, 'views'), path.join(__dirname, 'views/shared/')]);
// NUNJUCKS - CONFIGURATION & CUSTOM FILTERS
function setUpNunjucks(expressApp) {
const env = nunjucks.configure([path.join(__dirname, 'views'), path.join(__dirname, 'views/shared/')], {
autoescape: true, //default
throwOnUndefined: true, //for dev testing only
trimBlocks: true,
lstripBlocks: true,
noCache: false, //default
express: app
});
//custom Nunjucks filter to pass back into template!
env.addFilter('shorten', function (str, count) {
return str.slice(0, count || 5);
});
//an object looper. then do stuff with it
//apply the following inside the template form
env.addFilter('param', function (obj, mparam) {
for (const [key, value] of Object.entries(obj)) {
//example of whatever is needed...
if (mparam == value.param) {
return `${value.value}`;
}
}
});
}
setUpNunjucks(app);
//...other stuff...
//LISTEN
const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
console.log(`Sever started on port ${PORT}`);
});