What plugin does Webpack need to build multiple bundles?

Question

JavaScript

Ohio.
I want to improve the codebase of my pet project. There is now noodle code, and I decided to break it into modules. I've been poking around with Webpack for a while and have some idea about it. But now I’m in a stupor and I can’t find information on the most common case.
Bottom line: I have some core.js , and for several pages there is pageA.js and pageB.js . It's important for me to share it this way. Everything seems to be fine, but on a regular Webpack config, pageA.js is assembled with all the internals from core.js
To make it a little clearer, here:

# core/lib/func.js
export function sayHello () { /* ... */ }

# pageA/index.js
import { sayHello } from './../core/lib/func'
sayHello ()

And it turns out that sayHello is located both in core.js and in pageA.js (and you shouldn’t need to in
pageA.js ) bundle? (well, something like with externals: { jquery: 'jQuery' } )
(I just want core.js to be cached so that the code that is definitely needed here and there does not compete over the network every time)