treeshaking.js

// modules.js
export function drive(props) {
 return props.gas
}

export function fly(props) {
 return props.miles 
}

// main.js
import { drive } from modules;

/// some code
eventHandler = (event) => {
  event.preventDefault()
  drive({ gas: event.target.value })
}
/// some code

// fly() was never importent and won't be included in our bundle

Looks like line 20 should be something like this:
// fly() was never imported...