From 8e5adfbd7e605bda9c5e96c10e015b3dc0df688e Mon Sep 17 00:00:00 2001
From: Dan Abramov <dan.abramov@gmail.com>
Date: Wed, 21 Oct 2020 13:17:44 +0100
Subject: [PATCH] Remove usage of Array#fill (#20071)

---
 packages/react-reconciler/src/ReactFiberLane.js | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/packages/react-reconciler/src/ReactFiberLane.js b/packages/react-reconciler/src/ReactFiberLane.js
index 3dc89c45a956..027754dd76ee 100644
--- a/packages/react-reconciler/src/ReactFiberLane.js
+++ b/packages/react-reconciler/src/ReactFiberLane.js
@@ -640,7 +640,13 @@ export function higherLanePriority(
 }
 
 export function createLaneMap<T>(initial: T): LaneMap<T> {
-  return new Array(TotalLanes).fill(initial);
+  // Intentionally pushing one by one.
+  // https://v8.dev/blog/elements-kinds#avoid-creating-holes
+  const laneMap = [];
+  for (let i = 0; i < TotalLanes; i++) {
+    laneMap.push(initial);
+  }
+  return laneMap;
 }
 
 export function markRootUpdated(