Polymer Build cannot find ES6 classes which are not Polymer Elements - ecmascript-6

Question

We are using Polymer 2 for Building an App. We have Web Components deriving from Polymer Elements and pure ES6 classes that handles business logics. We have defined ES6 classes in html files and imported them via html import to where classes should be used.
myclass.html
<script>
class MyClass {
constructor(){
this.text = "MyClass";
}
getText(){
return this.text;
}
}
</script>
my-app.html
<link rel="import" href="../bower_components/polymer/polymer-element.html">
<link rel="import" href="myclass.html">
<dom-module id="my-app">
<template>
<div>{{text}}</div>
</template>
<script>
class MyApp extends Polymer.Element {
static get is() { return 'my-app'; }
static get properties() {
return {};
}
constructor(){
super();
var myObject = new MyClass();
this.text = myObject.getText();
}
}
window.customElements.define(MyApp.is, MyApp);
</script>
</dom-module>
This is running perfect with polymer serve via the source.
But when we do a Polymer Build and run via the build it gives the following error.
my-app.html:1 Uncaught ReferenceError: MyClass is not defined
at new MyApp (my-app.html:1)
at my-app.html:1

Answer 1

This was solved by modifying the MyClass like below. adding static get properties method.
<script>
class MyClass {
constructor(){
this.text = "MyClass";
}
static get properties() {
return {
};
}
getText(){
return this.text;
}
}