Issue #3443644: Fix eslint warnings

Closes #3443644

js/splashify_full_screen.js

 (function ($) {
-  Drupal.behaviors.splashifyBehavior.full_screen =
-    function (context, settings) {
-      var splash_height = $(window).height();
+  Drupal.behaviors.splashifyBehavior.full_screen = function (
+    context,
+    settings,
+  ) {
+    const splashHeight = $(window).height();
 
-      $('#splashify', context).once('splashify_open').each(function () {
-        var $splash = $(this);
+    // Open the splash div.
+    function openSplash($splash) {
+      const $body = $('body');
+      $body.addClass('splash-active');
+
+      const originalHeight = $splash.attr('originalheight');
+
+      if (originalHeight) {
+        $body[0].style.marginTop = `${originalHeight}px`;
+
+        const splashWrapper = document.querySelector('.splash-wrapper');
+        if (splashWrapper) {
+          splashWrapper.style.height = `${originalHeight}px`;
+        }
+      }
+
+      window.scrollTo(0, 0);
+    }
+
+    $('#splashify', context)
+      .once('splashify_open')
+      .each(function () {
+        const $splash = $(this);
 
         // Get the height of the div. Set it as a custom attribute.
         // Update the height to 0 and then show the div.
-        $('body').css('margin-top', splash_height);
-        $splash.attr('originalheight', splash_height + 'px');
-        $splash.css('position', 'absolute');
-        $splash.css('display', 'block');
+        document.body.style.marginTop = splashHeight;
+        $splash.setAttribute('originalheight', `${splashHeight}px`);
+        $splash.style.position = 'absolute';
+        $splash.style.display = 'block';
 
         // Open the splash.
         openSplash($splash);
 
         // Track scroll position to destroy splash
-        $(context).once('splashify_scroll').on('scroll.splash', function () {
-          var $object = $(this);
-          var scroll_position = $object.scrollTop();
-          if (scroll_position >= splash_height) {
-            $object.scrollTop(0);
-            // Destroy the splash div...they scrolled passed it.
-            var $body = $('body');
-            $body.removeClass('splash-active');
-            $body.css('margin-top', 0);
-            $('#splashify', context).css('height', 0);
-            $object.off('scroll.splash');
-          }
-        });
-      });
+        $(context)
+          .once('splashify_scroll')
+          .on('scroll.splash', function () {
+            const $object = $(this);
+            const scrollPosition = $object.scrollTop();
+            if (scrollPosition >= splashHeight) {
+              $object.scrollTop(0);
+              // Destroy the splash div, they scrolled passed it.
+              const $body = $('body');
+              $body.removeClass('splash-active');
+              $body[0].style.marginTop = '0';
 
-      // Open the splash div.
-      function openSplash($splash) {
-        var $body = $('body');
-        $body.addClass('splash-active');
-        $body.css('margin-top', $splash.attr('originalheight'));
-        $('.splash-wrapper').css('height', $splash.attr('originalheight'));
-        window.scrollTo(0, 0);
-      }
+              const splashify = document.getElementById('splashify');
+              if (splashify) {
+                splashify.style.height = '0';
+              }
 
-      // Close the splash div.
-      function closeSplash() {
-        var $body = $('body');
-        $body.removeClass('splash-active');
-        $body.css('margin-top', 0);
-        $('.splash-wrapper').css('height', 0);
-      }
+              $object.off('scroll.splash');
+            }
+          });
+      });
 
+    // Close the splash div.
+    function closeSplash() {
+      const $body = $('body');
+      $body.removeClass('splash-active');
+      $body[0].style.marginTop = '0';
+      document.querySelector('.splash-wrapper').style.height = '0';
     }
-
+  };
 })(jQuery);