# valtio

**Repository Path**: mirrors_fkhadra/valtio

## Basic Information

- **Project Name**: valtio
- **Description**: 💊 Valtio makes proxy-state simple  for React and Vanilla
- **Primary Language**: Unknown
- **License**: MIT
- **Default Branch**: main
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2022-01-11
- **Last Updated**: 2026-10-21

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

<img src="logo.svg" alt="valtio">
<br />
<br />

<code>npm i valtio</code> makes proxy-state simple

[![Build Status](https://img.shields.io/github/workflow/status/pmndrs/valtio/Lint?style=flat&colorA=000000&colorB=000000)](https://github.com/pmndrs/valtio/actions?query=workflow%3ALint)
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[![Version](https://img.shields.io/npm/v/valtio?style=flat&colorA=000000&colorB=000000)](https://www.npmjs.com/package/valtio)
[![Downloads](https://img.shields.io/npm/dt/valtio.svg?style=flat&colorA=000000&colorB=000000)](https://www.npmjs.com/package/valtio)
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#### Wrap your state object

Valtio turns the object you pass it into a self-aware proxy.

```jsx
import { proxy, useSnapshot } from 'valtio'

const state = proxy({ count: 0, text: 'hello' })
```

#### Mutate from anywhere

You can make changes to it in the same way you would to a normal js-object.

```jsx
setInterval(() => {
  ++state.count
}, 1000)
```

#### React via useSnapshot

Create a local snapshot that catches changes. Rule of thumb: read from snapshots, mutate the source. The component will only re-render when the parts of the state you access have changed, it is render-optimized.

```jsx
// This will re-render on `state.count` change but not on `state.text` change
function Counter() {
  const snap = useSnapshot(state)
  return (
    <div>
      {snap.count}
      <button onClick={() => ++state.count}>+1</button>
    </div>
  )
}
```

<details>
<summary>Note: useSnapshot returns a new proxy for render optimization.</summary>

Internally, `useSnapshot` calls `snapshot` in valtio/vanilla,
and wraps the snapshot object with another proxy to detect property access.
This feature is based on [proxy-compare](https://github.com/dai-shi/proxy-compare).

Two kinds of proxies are used for different purposes:

- `proxy()` from `valtio/vanilla` is for mutation tracking or write tracking.
- `createProxy()` from `proxy-compare` is for usage tracking or read tracking.
</details>

<details>
<summary>Use of `this` is for expert users.</summary>

Valtio tries best to handle `this` behavior
but it's hard to understand without familiarity.

```js
const state = proxy({ count: 0, inc() { ++this.count } })
state.inc() // `this` points to `state` and it works fine
const snap = useSnapshot(state)
snap.inc() // `this` points to `snap` and it doesn't work because snapshot is frozen
```

To avoid this pitfall, the recommended pattern is not to use `this` and prefer arrow function.

```js
const state = proxy({ count: 0, inc: () => { ++state.count } })
```

</details>

If you are new to this, it's highly recommended to use
[eslint-plugin-valtio](https://github.com/pmndrs/eslint-plugin-valtio).

#### Subscribe from anywhere

You can access state outside of your components and subscribe to changes.

```jsx
import { subscribe } from 'valtio'

// Suscribe to all state changes
const unsubscribe = subscribe(state, () => console.log('state has changed to', state))
// Unsubscribe by calling the result
unsubscribe()
```

You can also subscribe to a portion of state.

```jsx
const state = proxy({ obj: { foo: 'bar' }, arr: ['hello'] })

subscribe(state.obj, () => console.log('state.obj has changed to', state.obj))
state.obj.foo = 'baz'

subscribe(state.arr, () => console.log('state.arr has changed to', state.arr))
state.arr.push('world')
```

To subscribe to a primitive value of state, consider `subscribeKey` in utils.

```jsx
import { subscribeKey } from 'valtio/utils'

const state = proxy({ count: 0, text: 'hello' })
subscribeKey(state, 'count', (v) => console.log('state.count has changed to', v))
```

There is another util `watch` which might be convenient in some cases.

```jsx
import { watch } from 'valtio/utils'

const state = proxy({ count: 0 })
const stop = watch((get) => {
  console.log('state has changed to', get(state)) // auto-subscribe on use
})
```

#### Suspend your components

Valtio supports React-suspense and will throw promises that you access within a components render function. This eliminates all the async back-and-forth, you can access your data directly while the parent is responsible for fallback state and error handling.

```jsx
const state = proxy({ post: fetch(url).then((res) => res.json()) })

function Post() {
  const snap = useSnapshot(state)
  return <div>{snap.post.title}</div>
}

function App() {
  return (
    <Suspense fallback={<span>waiting...</span>}>
      <Post />
    </Suspense>
  )
}
```

#### Holding objects in state without tracking them

This may be useful if you have large, nested objects with accessors that you don't want to proxy. `ref` allows you to keep these objects inside the state model.

See [#61](https://github.com/pmndrs/valtio/issues/61) and [#178](https://github.com/pmndrs/valtio/issues/178) for more information.

```js
import { proxy, ref } from 'valtio'

const state = proxy({
  count: 0,
  dom: ref(document.body),
})
```

#### Update transiently (for often occuring state-changes)

You can read state in a component without causing re-render.

```jsx
function Foo() {
  const { count, text } = state
  // ...
```

Or, you can have more control with subscribing in useEffect.

```jsx
function Foo() {
  const total = useRef(0)
  useEffect(() => subscribe(state.arr, () => {
    total.current = state.arr.reduce((p, c) => p + c)
  }), [state.obj])
  // ...
```

#### Update synchronously

By default, state mutations are batched before triggering re-render.
Sometimes, we want to disable the batching.
The known use case of this is `<input>` [#270](https://github.com/pmndrs/valtio/issues/270).

```jsx
function TextBox() {
  const snap = useSnapshot(state, { sync: true })
  return <input value={snap.text} onChange={(e) => (state.text = e.target.value)} />
}
```

#### Dev tools

You can use [Redux DevTools Extension](https://github.com/zalmoxisus/redux-devtools-extension) for plain objects and arrays.

```jsx
import { devtools } from 'valtio/utils'

const state = proxy({ count: 0, text: 'hello' })
const unsub = devtools(state, 'state name')
```


<details>
  <summary>Manipulating state with Redux DevTools</summary>
The screenshot below shows how to use Redux DevTools to manipulate state. First select the object from the instances drop down. Then type in a JSON object to dispatch. Then click "Dispatch". Notice how it changes the state.

<img width="564" alt="image" src="https://user-images.githubusercontent.com/6372489/141134955-26e9ffce-1e2a-4c8c-a9b3-d9da739610fe.png">
</details>

#### Use it vanilla

Valtio is not tied to React, you can use it in vanilla-js.

```jsx
import { proxy, subscribe, snapshot } from 'valtio/vanilla'

const state = proxy({ count: 0, text: 'hello' })

subscribe(state, () => {
  console.log('state is mutated')
  const obj = snapshot(state) // A snapshot is an immutable object
})
```


#### `useProxy` macro

We have a convenient macro with
[babel-plugin-macros](https://www.npmjs.com/package/babel-plugin-macros).

```js
import { useProxy } from 'valtio/macro'

const Component = () => {
  useProxy(state)
  return (
    <div>
      {state.count}
      <button onClick={() => ++state.count}>+1</button>
    </div>
  )
}

// the code above becomes the code below.

import { useSnapshot } from 'valtio'

const Component = () => {
  const snap = useSnapshot(state)
  return (
    <div>
      {snap.count}
      <button onClick={() => ++state.count}>+1</button>
    </div>
  )
}
```

#### `derive` util

You can subscribe to some proxies and create a derived proxy.

```js
import { derive } from 'valtio/utils'

// create a base proxy
const state = proxy({
  count: 1,
})

// create a derived proxy
const derived = derive({
  doubled: (get) => get(state).count * 2,
})

// alternatively, attach derived properties to an existing proxy
derive({
  tripled: (get) => get(state).count * 3,
}, {
  proxy: state,
})
```

#### `proxyWithComputed` util

You can have computed values with dependency tracking with property access.
Dependency tracking in `proxyWithComputed` conflicts with the work in `useSnapshot`.
React users should prefer using `derive`.
`proxyWithComputed` works well for some edge cases and for vanilla-js users.

```js
import { proxyWithComputed } from 'valtio/utils'

const state = proxyWithComputed({
  count: 1,
}, {
  doubled: snap => snap.count * 2
})

// Computed values accept custom setters too:
const state2 = proxyWithComputed({
  firstName: 'Alec',
  lastName: 'Baldwin'
}, {
  fullName: {
    get: (snap) => snap.firstName + ' ' + snap.lastName,
    set: (state, newValue) => { [state.firstName, state.lastName] = newValue.split(' ') },
  }
})

// if you want a computed value to derive from another computed, you must declare the dependency first:
const state = proxyWithComputed({
  count: 1,
}, {
  doubled: snap => snap.count * 2,
  quadrupled: snap => snap.doubled * 2
})
```

The last use case fails to infer types in TypeScript
[#192](https://github.com/pmndrs/valtio/issues/192).

#### `proxyWithHistory` util

This is a utility function to create a proxy with snapshot history.

```js
import { proxyWithHistory } from 'valtio/utils'

const state = proxyWithHistory({ count: 0 })
console.log(state.value) // ---> { count: 0 }
state.value.count += 1
console.log(state.value) // ---> { count: 1 }
state.undo()
console.log(state.value) // ---> { count: 0 }
state.redo()
console.log(state.value) // ---> { count: 1 }
```

#### Plugins

- [eslint-plugin-valtio](https://github.com/pmndrs/eslint-plugin-valtio)

#### Recipes

Valtio is unopinionated about best practices.
The community is working on recipes on wiki pages.

- [How to organize actions](https://github.com/pmndrs/valtio/wiki/How-to-organize-actions)
- [How to persist states](https://github.com/pmndrs/valtio/wiki/How-to-persist-states)
- [How to use with context](https://github.com/pmndrs/valtio/wiki/How-to-use-with-context)
- [How to split and compose states](https://github.com/pmndrs/valtio/wiki/How-to-split-and-compose-states)