memoize common bases (#853)

* memoize common bases

* improve memoization

src/constants/index.ts

 import { ChainId, JSBI, Percent, Token, WETH, Pair, TokenAmount } from '@uniswap/sdk'
+
 import { fortmatic, injected, portis, walletconnect, walletlink } from '../connectors'
 
 export const ROUTER_ADDRESS = '0xf164fC0Ec4E93095b804a4795bBe1e041497b92a'
 
 // used to construct intermediary pairs for trading
-
 export const BASES_TO_CHECK_TRADES_AGAINST: { readonly [chainId in ChainId]: Token[] } = {
   [ChainId.MAINNET]: [
     WETH[ChainId.MAINNET],

src/hooks/Trades.ts

@@ -4,6 +4,7 @@ import flatMap from 'lodash.flatmap'
 
 import { useActiveWeb3React } from './index'
 import { usePairs } from '../data/Reserves'
+
 import { BASES_TO_CHECK_TRADES_AGAINST } from '../constants'
 
 function useAllCommonPairs(tokenA?: Token, tokenB?: Token): Pair[] {
@@ -11,7 +12,8 @@ function useAllCommonPairs(tokenA?: Token, tokenB?: Token): Pair[] {
 
   const bases = useMemo(() => BASES_TO_CHECK_TRADES_AGAINST[chainId as ChainId] ?? [], [chainId])
 
-  const allPairs = usePairs([
+  const allPairCombinations: [Token | undefined, Token | undefined][] = useMemo(
+    () => [
       // the direct pair
       [tokenA, tokenB],
       // token A against all bases
@@ -20,7 +22,11 @@ function useAllCommonPairs(tokenA?: Token, tokenB?: Token): Pair[] {
       ...bases.map((base): [Token | undefined, Token | undefined] => [tokenB, base]),
       // each base against all bases
       ...flatMap(bases, (base): [Token, Token][] => bases.map(otherBase => [base, otherBase]))
-  ])
+    ],
+    [tokenA, tokenB, bases]
+  )
+
+  const allPairs = usePairs(allPairCombinations)
 
   // only pass along valid pairs, non-duplicated pairs
   return useMemo(