From 1c87d33441f2c2c088a6398a08a871391f100067 Mon Sep 17 00:00:00 2001
From: David Himmelstrup <lemmih@gmail.com>
Date: Thu, 12 Oct 2017 17:58:42 +0200
Subject: [PATCH 1/2] Change 'lookUpwardForInlineStyle' from O(n^2) to O(n).

---
 src/model/immutable/EditorState.js | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/src/model/immutable/EditorState.js b/src/model/immutable/EditorState.js
index 1d833784f7..8069c773f6 100644
--- a/src/model/immutable/EditorState.js
+++ b/src/model/immutable/EditorState.js
@@ -652,17 +652,13 @@ function lookUpwardForInlineStyle(
   content: ContentState,
   fromKey: string,
 ): DraftInlineStyle {
-  var previousBlock = content.getBlockBefore(fromKey);
-  var previousLength;
-
-  while (previousBlock) {
-    previousLength = previousBlock.getLength();
-    if (previousLength) {
-      return previousBlock.getInlineStyleAt(previousLength - 1);
-    }
-    previousBlock = content.getBlockBefore(previousBlock.getKey());
-  }
+  var lastNonEmpty = content.getBlockMap()
+    .reverse()
+    .skipUntil((block, k) => k === fromKey && block.getLength())
+    .first();
 
+  if (lastNonEmpty)
+    return lastNonEmpty.getInlineStyleAt(lastNonEmpty.getLength() - 1);
   return OrderedSet();
 }
 

From 9a135472b13afa503c6a1061f277332c7bae9d88 Mon Sep 17 00:00:00 2001
From: David Himmelstrup <lemmih@gmail.com>
Date: Thu, 12 Oct 2017 19:32:11 +0200
Subject: [PATCH 2/2] lookUpwardForInlineStyle: Skip the current block to only
 look at the previous blocks.

---
 src/model/immutable/EditorState.js | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/model/immutable/EditorState.js b/src/model/immutable/EditorState.js
index 8069c773f6..8f5f547eba 100644
--- a/src/model/immutable/EditorState.js
+++ b/src/model/immutable/EditorState.js
@@ -654,7 +654,9 @@ function lookUpwardForInlineStyle(
 ): DraftInlineStyle {
   var lastNonEmpty = content.getBlockMap()
     .reverse()
-    .skipUntil((block, k) => k === fromKey && block.getLength())
+    .skipUntil((_, k) => k === fromKey)
+    .skip(1)
+    .skipUntil((block, _) => block.getLength())
     .first();
 
   if (lastNonEmpty)