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id: common-mistakes
title: Common Mistakes
sidebar_label: Common Mistakes
hide_title: true
description: Common Mistakes
---
import { InternalLinks } from '@site/src/components/InternalLinks'
# Common Mistakes
A somewhat common mistake is to write an <InternalLinks.InputSelectors text="input selector" /> that extracts a value or does some derivation, and a <InternalLinks.ResultFunction /> that just returns its result:
```ts
// ❌ BROKEN: this will not memoize correctly, and does nothing useful!
const brokenSelector = createSelector(
[(state: RootState) => state.todos],
todos => todos
)
```
Any <InternalLinks.ResultFunction /> that just returns its inputs is incorrect! The <InternalLinks.ResultFunction /> should always have the transformation logic.
Similarly:
```ts
// ❌ BROKEN: this will not memoize correctly!
const brokenSelector = createSelector(
[(state: RootState) => state],
state => state.todos
)
```
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