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---
id: handling-empty-array-results
title: Handling Empty Array Results
sidebar_label: Handling Empty Array Results
hide_title: true
description: Handling Empty Array Results
---
import Tabs from '@theme/Tabs'
import TabItem from '@theme/TabItem'
import { InternalLinks } from '@site/src/components/InternalLinks'
# Handling Empty Array Results
To reduce recalculations, use a predefined empty array when `array.filter` or similar methods result in an empty array.
So you can have a pattern like this:
{/* START: handling-empty-array-results/firstPattern.ts */}
<Tabs
groupId='language'
defaultValue='ts'
values={[
{label: 'TypeScript', value: 'ts'},
{label: 'JavaScript', value: 'js'},
]}>
<TabItem value='ts'>
```ts title="handling-empty-array-results/firstPattern.ts"
import { createSelector } from 'reselect'
export interface RootState {
todos: {
id: number
title: string
description: string
completed: boolean
}[]
}
const EMPTY_ARRAY: [] = []
const selectCompletedTodos = createSelector(
[(state: RootState) => state.todos],
todos => {
const completedTodos = todos.filter(todo => todo.completed === true)
return completedTodos.length === 0 ? EMPTY_ARRAY : completedTodos
}
)
```
</TabItem>
<TabItem value='js'>
```js title="handling-empty-array-results/firstPattern.js"
import { createSelector } from 'reselect'
const EMPTY_ARRAY = []
const selectCompletedTodos = createSelector([state => state.todos], todos => {
const completedTodos = todos.filter(todo => todo.completed === true)
return completedTodos.length === 0 ? EMPTY_ARRAY : completedTodos
})
```
</TabItem>
</Tabs>
{/* END: handling-empty-array-results/firstPattern.ts */}
Or to avoid repetition, you can create a wrapper function and reuse it:
{/* START: handling-empty-array-results/fallbackToEmptyArray.ts */}
<Tabs
groupId='language'
defaultValue='ts'
values={[
{label: 'TypeScript', value: 'ts'},
{label: 'JavaScript', value: 'js'},
]}>
<TabItem value='ts'>
```ts title="handling-empty-array-results/fallbackToEmptyArray.ts"
import { createSelector } from 'reselect'
import type { RootState } from './firstPattern'
const EMPTY_ARRAY: [] = []
export const fallbackToEmptyArray = <T>(array: T[]) => {
return array.length === 0 ? EMPTY_ARRAY : array
}
const selectCompletedTodos = createSelector(
[(state: RootState) => state.todos],
todos => {
return fallbackToEmptyArray(todos.filter(todo => todo.completed === true))
}
)
```
</TabItem>
<TabItem value='js'>
```js title="handling-empty-array-results/fallbackToEmptyArray.js"
import { createSelector } from 'reselect'
const EMPTY_ARRAY = []
export const fallbackToEmptyArray = array => {
return array.length === 0 ? EMPTY_ARRAY : array
}
const selectCompletedTodos = createSelector([state => state.todos], todos => {
return fallbackToEmptyArray(todos.filter(todo => todo.completed === true))
})
```
</TabItem>
</Tabs>
{/* END: handling-empty-array-results/fallbackToEmptyArray.ts */}
This way if the <InternalLinks.ResultFunction /> returns an empty array twice in a row, your component will not re-render due to a stable empty array reference:
```ts
const completedTodos = selectCompletedTodos(store.getState())
store.dispatch(addTodo())
console.log(completedTodos === selectCompletedTodos(store.getState())) //=> true
```
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