LWC File structure with many modulated JS files

helper.js

export function isFunction(value) {
    return 'Test'+ value;
}

lwc_pd_comp.html

<template>
    <lightning-card title="Details" icon-name="custom:custom14">
        <div class="slds-m-around_medium">
            <p>Hello, {greeting}!   {result}!</p>
            <lightning-input label="Name" value={greeting} onchange={changeHandler}></lightning-input>
        </div>
    </lightning-card>
</template>

lwc_pd_comp.js

import { LightningElement, track } from 'lwc';
import { isFunction } from './helper';
export default class HelloWorld extends LightningElement {
    @track greeting = 'world';
    @track result = 'init';
    changeHandler(event) {
        this.greeting = event.target.value;

        // Call the imported library function
        this.result = isFunction(' ' + event.target.value + ' ;'); 
    }
}

lwc_pd_comp.js-meta.xml

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata" fqn="helloWorld">
  <apiVersion>45.0</apiVersion>
  <isExposed>true</isExposed>
  <targets>
    <target>lightning__AppPage</target>
    <target>lightning__RecordPage</target>
    <target>lightning__HomePage</target>
  </targets>
</LightningComponentBundle>