# Hiding places

A hunt hides each card on a cell of a grid. `pickSpot` chooses one: lit, and not taken by another card. `useCardSpots` remembers the choice for the rest of the visit, so a card found on one tile is found on that tile again in a replay.

## Pick a cell

```ts
import { pickSpot } from "@react-cards-opening/core";

const levels = [0, 2, 0, 3, 1, 4]; // one number per cell, 0 is unlit
const cell = pickSpot(levels, [3]); // 1, 4 or 5: lit, and 3 is taken
```

Cards hide where there is something to find: an unlit cell is only used when nothing lit is free. The third argument is the random source. Pass `createRng(seed).next` to place cards the same way on every device.

## Remember it

```tsx
import { useCardSpots } from "@react-cards-opening/core";

const [spots, setSpots] = useCardSpots("deal:ada:2026:spots");
// spots["ash-phoenix"] === 142
```

It works like `useState`, with session storage behind it: the spots survive a reload and are gone when the tab closes. Pass `null` to keep them in memory. `CardHunt` does all of this for you through its `sessionKey` prop.

## Why not decide it up front

A cell is picked when its card's turn comes, not when the deal is made. Nothing in the page's HTML or state says where an unfound card is, so there is nothing to peek at in the inspector.

## Related

- [ScanGrid](https://bettertyped.github.io/react-cards-opening/docs/components/scan-grid/)
- [CardHunt](https://bettertyped.github.io/react-cards-opening/docs/components/card-hunt/)
- [Rolls and odds](https://bettertyped.github.io/react-cards-opening/docs/core/rolls/)
- [Beam and lock](https://bettertyped.github.io/react-cards-opening/docs/effects/beam-and-lock/)

Source: https://bettertyped.github.io/react-cards-opening/docs/core/spots/