[build]ES6 Bundle errors in browser with extending PolymerElement or mixin

[dman777]

Using Polymer 3 with cli 1.9.11 on linux system.

I have a Polymer 3 app that works with no issues. But if I build and bundle it I am having issues when bundled. I am only doing es6 for now. I have no idea how to even go about trouble shooting this..pretty stuck.

Polymer.json

      "builds": [
        {
          "name": "es6-bundled",
          "browserCapabilities": [
            "es2015"
          ],
          "js": {
            "minify": false,
            "transformModulesToAmd": true
          },
          "css": {
            "minify": false
          },
          "html": {
            "minify": false
          },
          "bundle": true,
          "addServiceWorker": false
        }
      ],

---

Error in browser:

    all-items:formatted:211 Uncaught TypeError: (0 , _mainApp.PauseForRipple) is not a function
        at user-login.js? [sm]:4

---

Code from bundle:

    define(["../main-app.js"], function(_mainApp) {
        "use strict";
    
        class UserLogin extends (0,
        _mainApp.PauseForRipple)(_mainApp.PolymerElement) {
            static get template() {
                return _mainApp.html`
          <style>
            :host {
              display: flex;
              align-items: center;

---

Original code before build:

    import { PauseForRipple } from '../mixins/pause-for-ripple-mixin.js';
    
    class UserLogin extends PauseForRipple(PolymerElement) {
      static get template() {
        return html`
          <style>
            :host {
              display: flex;
              align-items: center;
              justify-content: center;

---

Update I then removed the mixin and now browser is complaining about caught TypeError: Class extends value undefined is not a constructor or null

with the code:

  class UserLogin extends _mainApp.PolymerElement {
    static get template() {
      return _mainApp.html`

Please, if anyone can fix this or tell me what I am doing wrong.

[dman777]

Closing this.... the root cause is I had double import import './login/user-login.js'; in main-app.js.