Installs into .claude/skills of the current project.
Are you the author of Js Index Maps?
Add the live security badge to your README. It updates with every re-scan.
[](https://www.skillsdirectory.com/skills/anubhavg-icpl-js-index-maps)
---
name: js-index-maps
description: Build Index Maps for Repeated Lookups. Use when you need help with js index maps.
license: CC-BY-NC-SA-4.0
metadata:
risk: unknown
source: community
kind: mode
category: rules
---
## Build Index Maps for Repeated Lookups
Multiple `.find()` calls by the same key should use a Map.
**Incorrect (O(n) per lookup):**
```typescript
function processOrders(orders: Order[], users: User[]) {
return orders.map((order) => ({
...order,
user: users.find((u) => u.id === order.userId),
}));
}
```
**Correct (O(1) per lookup):**
```typescript
function processOrders(orders: Order[], users: User[]) {
const userById = new Map(users.map((u) => [u.id, u]));
return orders.map((order) => ({
...order,
user: userById.get(order.userId),
}));
}
```
Build map once (O(n)), then all lookups are O(1).
For 1000 orders × 1000 users: 1M ops → 2K ops.
