shallow

Shallow equality comparison function for Solid Store

Reference

shallow

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.

objA · T

The first value to compare.

objB · T

The second value to compare.

Returns

boolean · boolean

true if the values are shallowly equal, false otherwise.

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

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

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

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

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

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

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