JSFiddle - React, Tailwind, and code Playground

HTML

<script>Polymer={dom:'shadow'};</script>
<base href="https://polygit.org/*+:master/components/">
<link rel="import" href="polymer/polymer.html">
<link rel="import" href="paper-button/paper-button.html">

<dom-module id="x-foo">
  <template>
  <!-- Hackishly to give paper-button some properties. -->
  <paper-button made-up-bound-number="[[myMadeUpNumber]]"
                made-up-string="my made up string"
                made-up-bound-string="[[undefined]]my made up bound string"
                id="button"></paper-button>
  </template>
</dom-module>

<x-foo></x-foo>

JavaScript

Polymer({
  is: 'x-foo',
  properties: {
    myMadeUpNumber: {
      type: Number,
      value: 42,
    }
  },
  ready: function() {
    // Property defined dynamically and bound to [[myMadeUpNumber]] as Number.
    console.log(this.$.button.madeUpBoundNumber === 42);
    // Property not defined.
    console.log(this.$.button.madeUpString === undefined);
    // Property defined dynamically and bound to [[undefined]] + literal as String.
    console.log(this.$.button.madeUpBoundString === 'my made up bound string');
  },
});