Trying to setup shopify-api-node with express, where do I place the Shopify instance?

Trying to setup shopify-api-node with express, where do I place the Shopify instance? I'm using express.

In my app.js or in my public/javascripts folder?

https://github.com/monei/Shopify-api-node

const Shopify = require('shopify-api-node');

const shopify = new Shopify({
   shopName: 'your-shop-name',
   apiKey: 'your-api-key',
   password: 'your-app-password'
});

via CDBoi