custom element template

custom_element.html

<template>
  <style>
  </style>
</template>

<script>
  var doc = document.currentScript.ownerDocument;
  var ElementPrototype = Object.create(HTMLElement.prototype);

  ElementPrototype.createdCallback = function() {

    var shadow = this.createShadowRoot();
    var template = doc.querySelector('template');
    var clone = template.content.cloneNode(true);
    shadow.appendChild(clone);

  };

  var Element = document.registerElement('custom-element', {
    prototype: ElementPrototype
  });
</script>