Make plugin work in Firefox when CSS has html {scroll-behavior: smooth;}

kswedberg · kswedberg · commit 0987f08fd826 · 2016-01-16T15:20:07.000-05:00
diff --git a/src/jquery.smooth-scroll.js b/src/jquery.smooth-scroll.js
@@ -70,13 +70,21 @@
       }
     });
 
-    // If no scrollable elements, fall back to <body>,
-    // if it's in the jQuery collection
-    // (doing this because Safari sets scrollTop async,
-    // so can't set it to 1 and immediately get the value.)
     if (!scrollable.length) {
       this.each(function() {
-        if (this.nodeName === 'BODY') {
+        // If no scrollable elements and <html> has scroll-behavior:smooth because
+        // "When this property is specified on the root element, it applies to the viewport instead."
+        // and "The scroll-behavior property of the … body element is *not* propagated to the viewport."
+        // → https://drafts.csswg.org/cssom-view/#propdef-scroll-behavior
+        if (this === document.documentElement && $(this).css('scrollBehavior') === 'smooth') {
+          scrollable = [this];
+        }
+
+        // If still no scrollable elements, fall back to <body>,
+        // if it's in the jQuery collection
+        // (doing this because Safari sets scrollTop async,
+        // so can't set it to 1 and immediately get the value.)
+        if (!scrollable.length && this.nodeName === 'BODY') {
           scrollable = [this];
         }
       });
