Add Object.assign polyfill for IE11

layouts/partials/layout/javascript.html

@@ -25,6 +25,36 @@
 <!-- always use local version of the notes plugin since HTML file it requires isn't on CDN -->
 <script type="text/javascript" src="{{ "reveal-js/plugin/notes/notes.js" | relURL }}"></script>
 <script type="text/javascript">
+  // polyfill needed for IE11 and below
+  if (typeof Object.assign != 'function') {
+    // Must be writable: true, enumerable: false, configurable: true
+    Object.defineProperty(Object, "assign", {
+      value: function assign(target, varArgs) { // .length of function is 2
+        'use strict';
+        if (target == null) { // TypeError if undefined or null
+          throw new TypeError('Cannot convert undefined or null to object');
+        }
+
+        var to = Object(target);
+
+        for (var index = 1; index < arguments.length; index++) {
+          var nextSource = arguments[index];
+
+          if (nextSource != null) { // Skip over if undefined or null
+            for (var nextKey in nextSource) {
+              // Avoid bugs when hasOwnProperty is shadowed
+              if (Object.prototype.hasOwnProperty.call(nextSource, nextKey)) {
+                to[nextKey] = nextSource[nextKey];
+              }
+            }
+          }
+        }
+        return to;
+      },
+      writable: true,
+      configurable: true
+    });
+  }
   // Hugo lowercases all params and Reveal.js needs camelcase
   // So params in Hugo must be stored in snakecase and we camelize them here
   function camelize(map) {