conditionally load webcomponentsjs

webcoponents_support.js

var webComponentsSupported = ('registerElement' in document
  && 'import' in document.createElement('link')
  && 'content' in document.createElement('template'));

if (!webComponentsSupported) {
  var wcPoly = document.createElement('script');
  wcPoly.src = '/../bower_components/webcomponentsjs/webcomponents-lite.js';
  wcPoly.onload = lazyLoadPolymerAndElements;
  document.head.appendChild(wcPoly);
} else {
  lazyLoadPolymerAndElements();
}

function lazyLoadPolymerAndElements () {
  // Set up the element imports.
}