Register new event listeners in Polymer 1.0 after initial page load - dom

Question

In my Polymer 1.0 app, I have an on-tap function which dynamically adds another button into the page based on a few parameters in the form. The problem is that after adding the element and its event listener to the page, the new button won't actually fire the on-tap event.
JSFiddle for testing: https://jsfiddle.net/dme6tb7z/
index.html
<template is="dom-bind" id="app">
<div id="output"></div>
<paper-button id="myButton" on-tap="_addButton">Add Button</paper-button>
</template>
<script src="app.js"></script>
Here is where I create the new button and give it a listener in JS. Is there some kind of extra step I need to take so that Polymer can "see" the new on-tap event listener?
app.js
app._addButton = function(e) {
var el = document.createElement('paper-button');
el.innerHTML = "New Button";
el.id = "newbutton";
el.addEventListener('on-tap', '_testEvent');
this.$.output.appendChild(el);
// I also tried adding the event listener after appending
// the element to the page, like so...
// this.$.newButton.addEventListener('on-tap', '_testEvent');
};
app._testEvent = function(e) {
console.log(e);
};
EDIT
I'm thinking maybe I need to use something like Polymer.dom(parent).appendChild(node) to keep the two DOMs in sync. I did this in my app.js like so, but the event still doesn't fire.
app.js scope
(function(document) {
'use strict';
var app = document.querySelector('#app');
...
app._addButton = function(e) {
var el = document.createElement('paper-button');
el.innerHTML = "New Button";
el.id = "newbutton";
el.addEventListener('on-tap', '_testEvent');
var parentNode = document.getElementById('output');
Polymer.dom(parentNode).appendChild(el);
};
...
})(document);
Surely, there must be some way to add event listeners after initial page load? I've done this same thing countless times in other setups, but there's something weird going on with Polymer... I understand there are two DOMs to update, but I'm using the Polymer.dom method, so what in the world is preventing this from happening?
More Info
I noticed that after appending the new button to the page, I can successfully run this:
document.getElementById('newbutton').innerHTML = 'Hello World';
whereas this:
document.getElementById('newbutton').addEventListener('on-tap', '_testEvent');
has no effect (and no errors). Isn't that bizarre? Is there some sort of reinvented registration process in Polymer to add event listeners?

Answer 1

Okay, I think I figured it out.
First of all, on-tap in this context should be tap.
Second, the function name from JS should be formatted like this: this.functionName, or app.functionName if your template has an id of "app" and app is defined as var app = document.querySelector('#app');
All together, it looks like this:
var newElement = document.getElementById('newbutton');
newElement.addEventListener('tap', this._testEvent );
This doesn't work in the JS Fiddle for some reason, but does work in a real Polymer environment.