# react-hooks/memo-dependencies

> Require the dependency list of `useMemo` and `useCallback` to match what the callback reads

`useMemo` and `useCallback` keep their result until a value in the dependency list changes. If the callback reads a value that isn't in the list, the result stays the same when that value changes, and the component shows old data. A value in the list that the callback doesn't read makes it run again for nothing.

You don't have to list values that never change between renders, such as a `setState` function or a ref.

In `.ts` and `.tsx` files, the report comes with a suggestion that rewrites the list, which your editor can apply.

{/* Generated by src/codegen/lint-rule-docs.ts. Do not edit this section. */}

## Configure

Off by default. To turn it on:

```toml bunfig.toml
[lint.rules]
"react-hooks/memo-dependencies" = "error" # or "warn"
```

{/* End of the generated section. */}

## Examples

Reported, because `query` is missing from the list:

{/* bad */}
```jsx
import { useMemo } from "react";

function Results({ items, query }) {
  const visible = useMemo(() => items.filter(item => item.name.includes(query)), [items]);
  return <List items={visible} />;
}
```

Reported, because the callback doesn't read `theme`:

{/* bad */}
```jsx
import { useCallback } from "react";

function SaveButton({ save, draft, theme }) {
  const onClick = useCallback(() => save(draft), [save, draft, theme]);
  return <button onClick={onClick}>Save</button>;
}
```

Not reported:

{/* good */}
```jsx
import { useCallback, useMemo, useState } from "react";

function Results({ items, query }) {
  const [selected, setSelected] = useState(null);
  const visible = useMemo(() => items.filter(item => item.name.includes(query)), [items, query]);
  const onSelect = useCallback(item => setSelected(item.id), []);
  return <List items={visible} selected={selected} onSelect={onSelect} />;
}
```

## When not to use it

`react-hooks/exhaustive-deps` checks the same two hooks, and effects too. With both rules on, the same list is reported twice.