html-includes

# head
        <link rel="import" href="partials/header.html">
# body
        <div id="container"></div>
        <script>
          var link = document.querySelector('link[rel="import"]');

          // Clone the <template> in the import.
          var template = link.import.querySelector('template');
          var clone = document.importNode(template.content, true);

          document.querySelector('#container').parentNode.replaceChild(clone, document.querySelector('#container'));
        </script>