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# Store

The `Store` utility provides a string-backed key-value contract for Tempo features. Use
[`Store.memory`](/tempo/utilities/Store.memory) for process-local data or
[`Store.from`](/tempo/utilities/Store.from) to wrap another store.

## Contract

```ts
type CompareAndSet = (
  key: string,
  expected: string | null,
  value: string,
  options?: { expiresAt?: number },
) => MaybePromise<boolean>

type Store = {
  compareAndSet?: CompareAndSet | undefined
  getItem(key: string): MaybePromise<string | null | undefined>
  removeItem(key: string): MaybePromise<void>
  setItem(key: string, value: string): MaybePromise<void>
}

type Atomic = Store & {
  compareAndSet: CompareAndSet
}
```

### `compareAndSet`

Atomically replaces the current value when it equals `expected`. Multisig coordination uses this
method to preserve approvals submitted concurrently. A store passed to multisig coordination must
implement `compareAndSet` and satisfy `Store.Atomic`.

Set `options.expiresAt` to a Unix timestamp in milliseconds to expire the replacement value.
Omitting `expiresAt` stores the value until another write or removal. An atomic store must apply
the comparison, replacement, and expiration in one operation.

## See Also

* [`Store.from`](/tempo/utilities/Store.from)
* [`Store.memory`](/tempo/utilities/Store.memory)
* [`Store.session`](/tempo/utilities/Store.session)