fix onBlur logic to prevent unfocus on window unfocus

packages/slate-react/src/plugins/before.js

@@ -27,6 +27,7 @@ const debug = Debug('slate:before')
  */
 
 function BeforePlugin() {
+  let activeElement = null
   let compositionCount = 0
   let isComposing = false
   let isCopying = false
@@ -69,28 +70,34 @@ function BeforePlugin() {
     if (editor.props.readOnly) return true
 
     const { value } = change
-    const focusTarget = event.relatedTarget
+    const { relatedTarget, target } = event
+    const window = getWindow(target)
 
-    // focusTarget may be null when window itself being blurred
-    // (eg. when changing tabs), or when user clicks on elements
-    // without`tabindex` attribute.
-    if (focusTarget) {
+    // COMPAT: If the current `activeElement` is still the previous one, this is
+    // due to the window being blurred when the tab itself becomes unfocused, so
+    // we want to abort early to allow to editor to stay focused when the tab
+    // becomes focused again.
+    if (activeElement == window.document.activeElement) return true
+
+    // COMPAT: The `relatedTarget` can be null when the new focus target is not
+    // a "focusable" element (eg. a `<div>` without `tabindex` set).
+    if (relatedTarget) {
       const el = findDOMNode(editor)
-      // The event should be ignored if the focus returns to the editor from an
-      // embedded editable element (eg. an input element inside a void node).
-      if (focusTarget == el) return true
 
-      // when the focus moved from the editor to a void node spacer...
-      if (focusTarget.hasAttribute('data-slate-spacer')) return true
+      // COMPAT: The event should be ignored if the focus is returning to the
+      // editor from an embedded editable element (eg. an <input> element inside
+      // a void node).
+      if (relatedTarget == el) return true
 
-      // or to an editable element inside the editor but not into a void node
-      // (eg. a list item of the check list example).
-      if (
-        el.contains(focusTarget) &&
-        !findNode(focusTarget, value).isVoid
-      ) {
-        return true
-      }
+      // COMPAT: The event should be ignored if the focus is moving from the
+      // editor to inside a void node's spacer element.
+      if (relatedTarget.hasAttribute('data-slate-spacer')) return true
+
+      // COMPAT: The event should be ignored if the focus is moving to a non-
+      // editable section of an element that isn't a void node (eg. a list item
+      // of the check list example).
+      const node = findNode(relatedTarget, value)
+      if (el.contains(relatedTarget) && node && !node.isVoid) return true
     }
 
     debug('onBlur', { event })
@@ -323,6 +330,10 @@ function BeforePlugin() {
 
     const el = findDOMNode(editor)
 
+    // Save the new `activeElement`.
+    const window = getWindow(event.target)
+    activeElement = window.document.activeElement
+
     // COMPAT: If the editor has nested editable elements, the focus can go to
     // those elements. In Firefox, this must be prevented because it results in
     // issues with keyboard navigation. (2017/03/30)
@@ -407,6 +418,10 @@ function BeforePlugin() {
     if (isComposing) return true
     if (editor.props.readOnly) return true
 
+    // Save the new `activeElement`.
+    const window = getWindow(event.target)
+    activeElement = window.document.activeElement
+
     debug('onSelect', { event })
   }