From 8c6f4675beac9c71e96126dd6f06f455c4e4bf01 Mon Sep 17 00:00:00 2001
From: xobotyi <xog3@yandex.ru>
Date: Mon, 15 Jun 2020 14:37:37 +0300
Subject: [PATCH] feat(usePrevious): reworked the hook, now it is more
 memory-efficient.

Better to use two-variables exchange than `useEffect` with new
function on each render.
---
 src/usePrevious.ts | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/src/usePrevious.ts b/src/usePrevious.ts
index 658f0f68e6..69592b75ad 100644
--- a/src/usePrevious.ts
+++ b/src/usePrevious.ts
@@ -1,13 +1,11 @@
-import { useEffect, useRef } from 'react';
+import { useRef } from 'react';
 
-const usePrevious = <T>(state: T): T | undefined => {
-  const ref = useRef<T>();
+export default function usePrevious<T>(state: T): T | undefined {
+  const curRef = useRef<T>();
+  const prevRef = useRef<T>();
 
-  useEffect(() => {
-    ref.current = state;
-  });
+  prevRef.current = curRef.current;
+  curRef.current = state;
 
-  return ref.current;
-};
-
-export default usePrevious;
+  return prevRef.current;
+}