JB1905 / valtio

💊 Valtio makes proxy-state simple for React and Vanilla

npm i valtio makes proxy-state simple

Wrap your state object

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

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.

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.

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

Subscribe from anywhere

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

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.

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.

import { subscribeKey } from 'valtio/utils'

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

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.

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 pmndrs#62 for more information.

import { proxy, ref } from 'valtio'

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

Update transiently

You can subscribe a component to state without causing render, just stick the subscribe function into useEffect.

function Foo() {
  const ref = useRef(state.obj)
  useEffect(() => subscribe(state.obj, () => ref.current = state.obj), [state.obj])
  // ...

Update synchronously

By default, state mutations are batched before triggering re-render. Sometimes, we want to disable the batching.

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 for plain objects and arrays.

import { devtools } from 'valtio/utils'

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

Use it vanilla

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

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.

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 blow.

import { useSnapshot } from 'valtio'

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

Computed values

You can have computed values with dependency tracking. Dependency tracking in valtio conflicts with the work in useSnapshot. React users should consider using render functions (optionally useMemo) as a primary mean. Computed works well for some edge cases and for vanilla-js users.

addComputed

This is to add new computed to an existing proxy state. It can add computed to different proxy state.

import { addComputed } from 'valtio/utils'

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

// add computed to state
addComputed(state, {
  doubled: snap => snap.count * 2,
})

// create another proxy
const state2 = proxy({
  text: 'hello',
})

// add computed from state to state2
addComputed(state, {
  doubled: snap => snap.count * 2,
}, state2)

proxyWithComputed

This is to create a proxy state with computed at the same time. It can define setters optionally.

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
})