Update details polyfill

alphagov/govuk_elements#521

app/assets/javascripts/details.polyfill.js

@@ -6,10 +6,12 @@
 
 // http://www.sitepoint.com/fixing-the-details-element/
 
-(function () {
+;(function () {
   'use strict'
 
   var NATIVE_DETAILS = typeof document.createElement('details').open === 'boolean'
+  var KEY_ENTER = 13
+  var KEY_SPACE = 32
 
   // Add event construct for modern browsers or IE
   // which fires the callback with a pre-converted target reference
@@ -25,25 +27,50 @@
     }
   }
 
+  // Cross-browser character code / key pressed
+  function charCode (e) {
+    return (typeof e.which === 'number') ? e.which : e.keyCode
+  }
+
+  // Cross-browser preventing default action
+  function preventDefault (e) {
+    if (e.preventDefault) {
+      e.preventDefault()
+    } else {
+      e.returnValue = false
+    }
+  }
+
   // Handle cross-modal click events
   function addClickEvent (node, callback) {
-    // Prevent space(32) from scrolling the page
     addEvent(node, 'keypress', function (e, target) {
-      if (target.nodeName === 'SUMMARY') {
-        if (e.keyCode === 32) {
-          if (e.preventDefault) {
-            e.preventDefault()
+      // When the key gets pressed - check if it is enter or space
+      if (charCode(e) === KEY_ENTER || charCode(e) === KEY_SPACE) {
+        if (target.nodeName.toLowerCase() === 'summary') {
+          // Prevent space from scrolling the page
+          // and enter from submitting a form
+          preventDefault(e)
+          // Click to let the click event do all the necessary action
+          if (target.click) {
+            target.click()
           } else {
-            e.returnValue = false
+            // except Safari 5.1 and under don't support .click() here
+            callback(e, target)
           }
         }
       }
     })
-    // When the key comes up - check if it is enter(13) or space(32)
+
+    // Prevent keyup to prevent clicking twice in Firefox when using space key
     addEvent(node, 'keyup', function (e, target) {
-      if (e.keyCode === 13 || e.keyCode === 32) { callback(e, target) }
+      if (charCode(e) === KEY_SPACE) {
+        if (target.nodeName === 'SUMMARY') {
+          preventDefault(e)
+        }
+      }
     })
-    addEvent(node, 'mouseup', function (e, target) {
+
+    addEvent(node, 'click', function (e, target) {
       callback(e, target)
     })
   }
@@ -89,6 +116,10 @@
       details.__summary = details.getElementsByTagName('summary').item(0)
       details.__content = details.getElementsByTagName('div').item(0)
 
+      if (!details.__summary || !details.__content) {
+        return
+      }
+
       // If the content doesn't have an ID, assign it one now
       // which we'll need for the summary's aria-controls assignment
       if (!details.__content.id) {