[WIP] Scoll to selection tweaks, possible fix for #1032 (#1165)

* Scoll to selection tweaks, possible fix for #1032

* Update scroll-to-selection.js

* Update scroll-to-selection.js

packages/slate-react/src/utils/scroll-to-selection.js

@@ -2,6 +2,45 @@
 import getWindow from 'get-window'
 import isBackward from 'selection-is-backward'
 
+/**
+ * CSS overflow values that would cause scrolling.
+ *
+ * @type {Array}
+ */
+
+const OVERFLOWS = [
+  'auto',
+  'overlay',
+  'scroll',
+]
+
+/**
+ * Find the nearest parent with scrolling, or window.
+ *
+ * @param {el} Element
+ */
+
+function findScrollContainer(el) {
+  const window = getWindow(el)
+  let parent = el.parentNode
+  let scroller = window
+  
+  while (!scroller) {
+    if (!parent.parentNode) break
+    const style = window.getComputedStyle(parent)
+    const { overflowY } = style
+
+    if (OVERFLOWS.includes(overflowY)) {
+      scroller = parent
+      break
+    }
+    
+    parent = parent.parentNode
+  }
+  
+  return scroller
+}
+
 /**
  * Scroll the current selection's focus point into view if needed.
  *
@@ -12,22 +51,47 @@ function scrollToSelection(selection) {
   if (!selection.anchorNode) return
 
   const window = getWindow(selection.anchorNode)
+  const scroller = findScrollContainer(selection.anchorNode)
+  const isWindow = scroller == window
   const backward = isBackward(selection)
   const range = selection.getRangeAt(0)
   const rect = range.getBoundingClientRect()
-  const { innerWidth, innerHeight, pageYOffset, pageXOffset } = window
-  const top = (backward ? rect.top : rect.bottom) + pageYOffset
-  const left = (backward ? rect.left : rect.right) + pageXOffset
+  let width
+  let height
+  let yOffset
+  let xOffset
   
-  const x = left < pageXOffset || innerWidth + pageXOffset < left
-    ? left - innerWidth / 2
-    : pageXOffset
+  if (isWindow) {
+    const { innerWidth, innerHeight, pageYOffset, pageXOffset } = scroller
+    width = innerWidth
+    height = innerHeight
+    yOffset = pageYOffset
+    xOffset = pageXOffset
+  } else {
+    const { offsetWidth, offsetHeight, scrollTop, scrollLeft } = scroller
+    width = offsetWidth
+    height = offsetHeight
+    yOffset = scrollTop
+    xOffset = scrollLeft
+  }
   
-  const y = top < pageYOffset || innerHeight + pageYOffset < top
-    ? top - innerHeight / 2
-    : pageYOffset
+  const top = (backward ? rect.top : rect.bottom) + yOffset
+  const left = (backward ? rect.left : rect.right) + xOffset
   
+  const x = left < yOffset || innerWidth + xOffset < left
+    ? left - width / 2
+    : xOffset
+
+  const y = top < yOffset || height + yOffset < top
+    ? top - height / 2
+    : yOffset
+
+  if (isWindow) {
     window.scrollTo(x, y)
+  } else {
+    scroller.scrollTop = scroller.scrollTop + y
+    scroller.scrollLeft = scroller.scrollLeft + x
+  }
 }
 
 /**