From 3686506f2a6dc3eb83c51b4f611cc3d93cd466d5 Mon Sep 17 00:00:00 2001
From: Moody Salem <moody.salem@gmail.com>
Date: Fri, 23 Jul 2021 09:27:23 -0500
Subject: [PATCH] perf: remove extra spread operators from the combine maps
 function

---
 src/state/lists/hooks.ts | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/src/state/lists/hooks.ts b/src/state/lists/hooks.ts
index 1243835c4f..c75530c0e1 100644
--- a/src/state/lists/hooks.ts
+++ b/src/state/lists/hooks.ts
@@ -47,16 +47,29 @@ export function useAllLists(): AppState['lists']['byUrl'] {
   return useAppSelector((state) => state.lists.byUrl)
 }
 
-// TODO: return a proxy instead of doing a reduce
+/**
+ * Combine the tokens in map2 with the tokens on map1, where tokens on map1 take precedence
+ * @param map1 the base token map
+ * @param map2 the map of additioanl tokens to add to the base map
+ */
 export function combineMaps(map1: TokenAddressMap, map2: TokenAddressMap): TokenAddressMap {
-  const chainIds = Object.keys({ ...map1, ...map2 }).map((id) => parseInt(id))
-  return chainIds.reduce(
-    (acc, chainId) => ({
-      ...acc,
-      [chainId]: { ...map2[chainId], ...map1[chainId] },
-    }),
-    {}
-  )
+  const chainIds = Object.keys(
+    Object.keys(map1)
+      .concat(Object.keys(map2))
+      .reduce<{ [chainId: string]: true }>((memo, value) => {
+        memo[value] = true
+        return memo
+      }, {})
+  ).map((id) => parseInt(id))
+
+  return chainIds.reduce<Mutable<TokenAddressMap>>((memo, chainId) => {
+    memo[chainId] = {
+      ...map2[chainId],
+      // map1 takes precedence
+      ...map1[chainId],
+    }
+    return memo
+  }, {}) as TokenAddressMap
 }
 
 // merge tokens contained within lists from urls