---
title: peek
description: "Reads a value without affecting eviction order — useful for inspection or metrics without disturbing LRU/LFU/MRU/MFU state."
type: package
package: "@zap-studio/cache"
---

`peek(key)` reads a value the same way `get(key)` does, but without notifying the eviction policy — so it never affects `lru()`/`mru()` recency or `lfu()`/`mfu()` frequency. It still respects TTL: an expired entry is removed and `undefined` is returned, same as `get`.

```ts
cache.peek("a"); // same as get(), but no recency/frequency bump
```

## Why It Exists

Sometimes you need to look at a cached value without that look counting as "use" — for example, inspecting cache contents for metrics or debugging, or checking a value opportunistically without wanting it to outlive entries that are actually being used.

```ts
const cache = createCache<string, number>(2); // lru() by default

cache.set("a", 1);
cache.set("b", 2);
cache.peek("a"); // does not mark "a" as recently used
cache.set("c", 3); // evicts "a" anyway — peek didn't save it

cache.has("a"); // false
cache.has("b"); // true
```

Compare with `get`, which would have kept `"a"` alive by bumping its recency:

```ts
const cache = createCache<string, number>(2);

cache.set("a", 1);
cache.set("b", 2);
cache.get("a"); // marks "a" as recently used
cache.set("c", 3); // evicts "b" instead

cache.has("a"); // true
cache.has("b"); // false
```

## Missing and Expired Keys

`peek` returns `undefined` for a missing key, and also for an expired key — removing it from the store and firing [`onEvict`](/cache/on-evict) if configured, exactly like `get` does.

```ts
cache.peek("missing"); // undefined

cache.set("a", 1, { ttl: 100 });
// ... 101ms later ...
cache.peek("a"); // undefined — expired and removed, onEvict fires
```

## See Also

- [Eviction Policies](/cache/eviction-policies) — what `get`/`set` bump that `peek` skips
- [TTL](/cache/ttl)