How to change the state of a Vue variable in an external JS file?

Let’s say I have a vue component:

import {foo} from 'path';
export default {
  data() {
    return {
      inputValue: "",
    };
  },

How can I create imported JavaScript function that takes an inputValue, modifies it, and then returns the updated state of the inputValue to the vue component?

I tried passing the inputValue as a parameter to the function foo(), changing its value inside the function, and returning it, but I got an undefined value.

I’m creating an external function because modifying inputValue is just a small part of the function, and I don’t want my code to become cluttered.