Fix undefined access error

app/accounts/[id]/settings.tsx

@@ -5,7 +5,11 @@ import { Divider, List, Text } from "react-native-paper";
 import { useAccount } from "../../../components/AccountContext";
 import { DeleteAccountDialog } from "../../../components/DeleteAccountDialog";
 import { Screen } from "../../../components/Screen";
-import { getLastEventId, listCategory } from "../../../lib/account";
+import {
+  getLastEvent,
+  getLastEventId,
+  listCategory,
+} from "../../../lib/account";
 import { deleteAccountFromLocal } from "../../../lib/account-local-storage";
 
 export default function Settings(): JSX.Element {
@@ -58,7 +62,7 @@ export default function Settings(): JSX.Element {
         <Divider style={{ width: "100%" }} />
         <List.Item
           title="Last updated"
-          description={`${account.events[account.events.length - 1].at}`}
+          description={`${getLastEvent(account).at}`}
           style={{ width: "100%" }}
         />
         <Divider style={{ width: "100%" }} />

components/AccountContext.tsx

@@ -51,5 +51,5 @@ export function useAccount(
         .then((account) => setAccount(account));
     }
   }, deps);
-  return [accounts[accountId], setAccount];
+  return [accounts[accountId] ?? null, setAccount];
 }

lib/account.ts

@@ -115,9 +115,16 @@ export const deleteTransaction = (
   return [applyEvent(self, event), event];
 };
 
+// query
+export function getLastEvent(self: Account): AccountEvent {
+  const lastEvent = self.events[self.events.length - 1];
+  if (lastEvent === undefined) throw new Error("assertion error");
+  return lastEvent;
+}
+
 // query
 export const getLastEventId = (self: Account): string => {
-  return self.events[self.events.length - 1].id;
+  return getLastEvent(self).id;
 };
 
 // query
@@ -136,11 +143,13 @@ export const listCategory = (
 
 export const restoreAccount = (events: AccountEvent[]): Account => {
   if (events.length === 0) throw new Error("events is empty");
+  const firstEvent = events[0];
+  if (firstEvent === undefined) throw new Error("assertion error");
   return events
     .slice(1)
     .reduce(
       (state, event) => applyEvent(state, event),
-      applyEvent(null, events[0])
+      applyEvent(null, firstEvent)
     );
 };
 

tsconfig.json

@@ -1,6 +1,7 @@
 {
   "extends": "expo/tsconfig.base",
   "compilerOptions": {
+    "noUncheckedIndexedAccess": true,
     "strict": true
   }
 }