Polymer/Webcomponents conditional polyfill

imports.html

<script>
  if ('registerElement' in document
    && 'createShadowRoot' in HTMLElement.prototype
    && 'import' in document.createElement('link')
    && 'content' in document.createElement('template')) {
    // We're using a browser with native WC support!
  } else {
    document.write(
      '<script src="https:\/\/cdnjs.cloudflare.com/ajax/libs/webcomponentsjs/0.6.0/webcomponents.min.js"><\/script>'
    );
  }
</script>
<link rel="import" href="my-custom-component.html">

<!-- credit to Glen Maddern, https://github.com/geelen/x-gif -->