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# useMemo

## Syntax

`useMemo(computation: Function, cacheKeyProperties: Array<Any>): Any`

The `useMemo` hook allows you to persist computed values across state hook evaluations. It is very similar to `useCallback` but, when needed, it'll execute the function passed to it and return the computed value.

## Storing an expensive computation

```javascript
function useSlug({ text }) {
    const slug = useMemo(() => slugify(text), [text]);
    return slug;
}
```

In the above example, we memoize the call to an expensive `slugify` function, which will translate a string such as "Separation of Concerns" to "separation-of-concerns". `useMemo` enables us to avoid recomputing that value until the text we wanted to `slugify` actually changed.

As with `useCallback` and `useEffect` you should always try to minimise dependencies, however, due to the nature of `useMemo`, you'll want to depend on values instead of accessor functions, just like with `useEffect`.