How can I output a variable to another file?

Question

Express.js

Good afternoon, I'm doing a project on node js, express, handlebars. Faced a problem with exporting a variable to another file that is connected to the html page.
This writes if connected via module exports and require - Uncaught ReferenceError: require is not defined at main.js
: then I doubt it very much, since everything is written correctly, like

export let a = 1
import {a} from '../database/itemsSelect'

The main question is how can I export a large block of data and work with them, and after outputting from js to html, I don’t need to send to html right away, I need to work with the js file, but in another
Just like a regular html css js stack is the same