Atom

The Atom type represents a writable reactive state container

Atom

The Atom<T> type represents a writable reactive state container that can be read, written, and subscribed to for changes.

Type Definition

interface Atom<T> extends BaseAtom<T> {
  /** Sets the value of the atom using a function. */
  set: ((fn: (prevVal: T) => T) => void) & ((value: T) => void)
}

interface BaseAtom<T> extends Subscribable<T>, Readable<T> {}

Properties

set

Sets the value of the atom. Can be called with either a new value directly or a function that receives the previous value and returns the new value.

Type:

((fn: (prevVal: T) => T) => void) & ((value: T) => void)

get

Inherited from Readable<T>. Returns the current value of the atom.

Type:

() => T

subscribe

Inherited from Subscribable<T>. Subscribes to changes in the atom’s value.

Type:

((observer: Observer<T>) => Subscription) &
  ((
    next: (value: T) => void,
    error?: (error: any) => void,
    complete?: () => void,
  ) => Subscription)

Usage Examples

Setting values directly

import { atom } from '@tanstack/store'

const counterAtom = atom(0)

// Set a new value directly
counterAtom.set(5)

console.log(counterAtom.get()) // 5

Setting values with a function

import { atom } from '@tanstack/store'

const counterAtom = atom(0)

// Update based on previous value
counterAtom.set((prev) => prev + 1)

console.log(counterAtom.get()) // 1

Reading and subscribing

import { atom } from '@tanstack/store'

const counterAtom = atom(0)

// Subscribe to changes
const subscription = counterAtom.subscribe((value) => {
  console.log('Counter changed:', value)
})

// Update the atom
counterAtom.set(1) // Logs: "Counter changed: 1"
counterAtom.set(2) // Logs: "Counter changed: 2"

// Clean up
subscription.unsubscribe()

Working with complex state

import { atom } from '@tanstack/store'

interface User {
  name: string
  age: number
}

const userAtom = atom<User>({ name: 'John', age: 30 })

// Update specific properties
userAtom.set((prev) => ({ ...prev, age: prev.age + 1 }))

console.log(userAtom.get()) // { name: 'John', age: 31 }

Related Types

• ReadonlyAtom - A read-only version of Atom
• Observer - The observer pattern for subscriptions
• Subscription - The subscription object returned by subscribe
• AtomOptions - Configuration options for creating atoms