Make runkit script async.

Author: jdalton

_config.yml

@@ -77,6 +77,7 @@ vendor:
 
   js:
     - href: https://embed.runkit.com/
+      async: true
 
     - href: https://cdn.jsdelivr.net/g/fuse@2.6.1,react@15.4.0(react.min.js+react-dom.min.js
       integrity: sha384-txLSiuN1HJSO1or/mE1Y6bvgD0cV3WA6Ss7rs9WqvPQ3zthR8w/DzHpB+DVTDAMz

_layouts/docs.html

@@ -29,11 +29,7 @@
     {% assign resources = resources | unshift:site.builds[page.version] %}
     {% for res in resources %}
       {% assign protocol = res.href | slice:0,6 %}
-      {% if res.integrity and protocol == 'https:' %}
-    <script src="{{ res.href }}" integrity="{{ res.integrity }}" crossorigin></script>
-      {% else %}
-    <script src="{{ res.href }}"></script>
-      {% endif %}
+    <script src="{{ res.href }}"{% if res.integrity and protocol == 'https:' %} integrity="{{ res.integrity }}" crossorigin{% endif %}{% if res.async %} async{% endif %}></script>
     {% endfor %}
     <script src="/assets/js/docs.js"></script>
   {% endcapture %}

assets/js/docs.js

@@ -425,6 +425,10 @@
         button.textContent = 'Try in REPL'
         button.style.display = navigator.onLine ? '' : 'none'
         button.addEventListener('click', function() {
+          if (typeof RunKit === 'undefined') {
+            return
+          }
+
           var source = div.innerText
           parent.removeChild(div)
           parent.removeChild(button)