> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/TanStack/store/llms.txt
> Use this file to discover all available pages before exploring further.

# shallow

> Shallow equality comparison function for Solid Store

## Reference

### `shallow`

```tsx theme={null}
function shallow<T>(objA: T, objB: T): boolean
```

A utility function that performs shallow equality comparison between two values. Used as the default equality function in `useStore` to prevent unnecessary signal updates.

<ParamField path="objA" type="T">
  The first value to compare.
</ParamField>

<ParamField path="objB" type="T">
  The second value to compare.
</ParamField>

### Returns

<ResponseField name="boolean" type="boolean">
  `true` if the values are shallowly equal, `false` otherwise.
</ResponseField>

## Comparison Behavior

The `shallow` function handles various data types:

* **Reference equality**: Returns `true` if `Object.is(objA, objB)`
* **Primitives/null**: Returns `false` if either value is not an object
* **Map**: Compares size and all entries using `Object.is`
* **Set**: Compares size and all values for presence
* **Date**: Compares timestamps using `getTime()`
* **Objects**: Compares own properties using `Object.is`

## Usage

### Default Behavior

```tsx theme={null}
import { useStore } from '@tanstack/solid-store'
import { store } from './store'

// shallow is used by default
function Component() {
  const user = useStore(store, (state) => state.user)
  return <div>{user().name}</div>
}
```

### Explicit Usage

```tsx theme={null}
import { useStore, shallow } from '@tanstack/solid-store'
import { store } from './store'

function UserCard() {
  const user = useStore(
    store,
    (state) => ({
      name: state.name,
      email: state.email,
      role: state.role
    }),
    { equal: shallow }
  )

  return (
    <div>
      <h2>{user().name}</h2>
      <p>{user().email}</p>
    </div>
  )
}
```

### Reference Equality

```tsx theme={null}
import { useStore } from '@tanstack/solid-store'
import { store } from './store'

// Use strict reference equality for arrays
function TodoList() {
  const todos = useStore(
    store,
    (state) => state.todos,
    { equal: (a, b) => a === b }
  )

  return (
    <ul>
      <For each={todos()}>
        {(todo) => <li>{todo.text}</li>}
      </For>
    </ul>
  )
}
```

### Array Operations

```tsx theme={null}
import { For } from 'solid-js'
import { useStore, shallow } from '@tanstack/solid-store'
import { store } from './store'

function FilteredList() {
  // Shallow comparison on filtered results
  const activeItems = useStore(
    store,
    (state) => state.items.filter(item => item.active),
    { equal: shallow }
  )

  return (
    <ul>
      <For each={activeItems()}>
        {(item) => <li>{item.name}</li>}
      </For>
    </ul>
  )
}
```

### Object Slices

```tsx theme={null}
import { useStore, shallow } from '@tanstack/solid-store'
import { store } from './store'

function Settings() {
  const settings = useStore(
    store,
    (state) => ({
      theme: state.settings.theme,
      language: state.settings.language,
      notifications: state.settings.notifications
    }),
    { equal: shallow }
  )

  return (
    <div>
      <p>Theme: {settings().theme}</p>
      <p>Language: {settings().language}</p>
    </div>
  )
}
```

### With createMemo

```tsx theme={null}
import { createMemo } from 'solid-js'
import { useStore, shallow } from '@tanstack/solid-store'
import { store } from './store'

function Dashboard() {
  const stats = useStore(
    store,
    (state) => ({
      users: state.users.length,
      posts: state.posts.length
    }),
    { equal: shallow }
  )

  const total = createMemo(() => stats().users + stats().posts)

  return <div>Total items: {total()}</div>
}
```

## Notes

* Used as the **default equality function** in `useStore`
* Only compares **own properties** at the first level (shallow)
* For nested objects, only the reference is compared
* Handles special object types: Map, Set, Date
* Optimized for Solid's fine-grained reactivity system
* Prevents unnecessary signal updates when object contents are equivalent
* More efficient than deep equality for most reactive scenarios