Layout Grid Examples: Fix NUX close button for IE (pull #548)

Fix issue #531: NUX instructions not closing as expected with IE11.

A loop was created on focus,
where the instructions were displayed and then dismissing the instructions set focus to the element that displayed the instructions on focus.
This happened because the once option was used for the event listener, which is not supported in IE11.

This commit adds an event listener that, when fired, removed the event listener and setup the instructions and close listeners/ handlers.

examples/grid/js/layoutGrids.js

@@ -35,31 +35,24 @@ window.addEventListener('load', function () {
 
   var gridNUX = document.getElementById('grid-nux');
   var firstGridCell = document.querySelector('#ex1 [tabindex="0"]');
-  firstGridCell.addEventListener(
-    'focus',
-    function () {
-      aria.Utils.removeClass(gridNUX, 'hidden');
-    },
-    {
-      once: true
-    }
-  );
-
   var NUXclose = document.getElementById('close-nux-button');
   var closeNUX = function () {
     aria.Utils.addClass(gridNUX, 'hidden');
-    try {
-      firstGridCell.focus();
-    }
-    catch (error) { }
+    firstGridCell.focus();
   };
-  NUXclose.addEventListener('click', closeNUX);
-  NUXclose.addEventListener('keyup', function (event) {
-    var key = event.which || event.keyCode;
-    if (key === aria.KeyCode.RETURN) {
-      closeNUX();
-    }
-  });
+  var setupInstructions = function () {
+    firstGridCell.removeEventListener('focus', setupInstructions);
+    aria.Utils.removeClass(gridNUX, 'hidden');
+
+    NUXclose.addEventListener('click', closeNUX);
+    NUXclose.addEventListener('keyup', function (event) {
+      if (event.which === aria.KeyCode.RETURN) {
+        closeNUX();
+      }
+    });
+  };
+
+  firstGridCell.addEventListener('focus', setupInstructions);
 });
 
 function PillList (grid, input, submitButton, formUpdateText) {