From b03752cbe0b5f20708cf49e4e966bfa6d0b1587d Mon Sep 17 00:00:00 2001
From: Lauren Tan <poteto@users.noreply.github.com>
Date: Mon, 17 Oct 2022 16:07:50 -0400
Subject: [PATCH] Use for loop instead of Array.prototype.fill

Some prior [microbenchmarking](https://jsbench.me/7ol98ws520/1) showed that a
for loop outperformed `fill` (which is about ~60% slower). This is the same
approach we use in the latest useMemoCache PR
---
 .../forget/packages/react-forget-runtime/index.js     | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/compiler/forget/packages/react-forget-runtime/index.js b/compiler/forget/packages/react-forget-runtime/index.js
index 3f0feafdc8..7ae3cb82cb 100644
--- a/compiler/forget/packages/react-forget-runtime/index.js
+++ b/compiler/forget/packages/react-forget-runtime/index.js
@@ -16,9 +16,12 @@ const {
 
 export const $empty = Symbol.for("react.usememocache_sentinel");
 
-export function unstable_useMemoCache(i) {
+export function unstable_useMemoCache(size) {
   "use no forget";
-  const $ = new Array(i).fill($empty);
+  const $ = new Array(size);
+  for (let ii = 0; ii < size; ii++) {
+    $[ii] = $empty;
+  }
   return useRef($).current;
 }
 
@@ -78,7 +81,9 @@ export function $endLazy() {
 }
 
 export function $reset($) {
-  $.fill($empty);
+  for (let ii = 0; ii < $.length; ii++) {
+    $[ii] = $empty;
+  }
 }
 
 export function $makeReadOnly() {