From fe660672cb5030e0f780d273798eec894209bbfa Mon Sep 17 00:00:00 2001
From: Nick Colley <nick.colley@digital.cabinet-office.gov.uk>
Date: Wed, 11 Dec 2019 17:47:56 +0000
Subject: [PATCH] Fix *ElementSibiling polyfills

In Internet Explorer 8 errors are thrown when checking the nodeType as nextSibiling is undefined, so to fix this issue we should first check if there is a next sibiling which matches the conditional in the while loop.

Fixes https://github.com/alphagov/govuk-frontend/issues/1490
---
 .../vendor/polyfills/Element/prototype/nextElementSibling.js    | 2 +-
 .../polyfills/Element/prototype/previousElementSibling.js       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/govuk/vendor/polyfills/Element/prototype/nextElementSibling.js b/src/govuk/vendor/polyfills/Element/prototype/nextElementSibling.js
index ec3c615496c..35592a91308 100644
--- a/src/govuk/vendor/polyfills/Element/prototype/nextElementSibling.js
+++ b/src/govuk/vendor/polyfills/Element/prototype/nextElementSibling.js
@@ -18,7 +18,7 @@ import '../../Element'
         get: function(){
           var el = this.nextSibling;
           while (el && el.nodeType !== 1) { el = el.nextSibling; }
-          return (el.nodeType === 1) ? el : null;
+          return (el && el.nodeType === 1) ? el : null;
         }
       });
 
diff --git a/src/govuk/vendor/polyfills/Element/prototype/previousElementSibling.js b/src/govuk/vendor/polyfills/Element/prototype/previousElementSibling.js
index 1184a0a3e31..a211fd96f3e 100644
--- a/src/govuk/vendor/polyfills/Element/prototype/previousElementSibling.js
+++ b/src/govuk/vendor/polyfills/Element/prototype/previousElementSibling.js
@@ -16,7 +16,7 @@ import '../../Element'
         get: function(){
           var el = this.previousSibling;
           while (el && el.nodeType !== 1) { el = el.previousSibling; }
-          return (el.nodeType === 1) ? el : null;
+          return (el && el.nodeType === 1) ? el : null;
         }
       });