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2.x to 3.0 Alpha

Version 3.0 is a big change focused mainly in four areas. If you have any trouble with the migration join the community on Discord or Github and we will help.

1. Types

The types were fully rewritten from scratch, fixing many bugs especially around Promises and nullability, and many of the types were renamed. You may need to rename some of your type imports.

2. Computed/Proxy

computed/proxy are no longer separate concepts, they’re just a function in an observable. If you were using computed you can just use observable now, and if you were using computed as a child of an observable, you can remove computed and use just a function. The old behavior will still work for now, but the new way is more efficient and computed will be deprecated in a later version.

See Computed Observables for more details.

// Change
const compValue$ = computed(() => /* ... */)
// to
const compValue$ = observable(() => /* ... */)
// Change
const state$ = observable(() => ({
value: 1,
comp: computed(() => state$.value.get())
// to
const state$ = observable(() => ({
value: 1,
comp: () => state$.value.get()

proxy is now just a function with a string parameter.

See Computed Observables for more details.

// Change
const state$ = observable({
items: { test1: { text: 'hi' }, test2: { text: 'hello' } },
itemText: proxy((key) => {
return state$.items[key]['text'];
// To
const state$ = observable({
items: { test1: { text: 'hi' }, test2: { text: 'hello' } },
texts: (key: string) => {
return state$.items[key]['text']

And you can use useObservable in the same way that you used to use useComputed:

// Change
const state$ = useComputed(() => state$.text.get())
// To
const state$ = useObservable(() => state$.text.get())

3. Persist

Persistence works in the same way but the API is changed for clarity and new features with the new more robust sync system. persistObservable is changed to syncObservable and the persisting features are under the persist option instead of local.

Additionally, persistObservable was inserting a state property for the sync state, which caused compatibility issues with data that had its own state property. So the sync state is now accessible separately with syncState.

Likewise, configureObservablePersistence is renamed to configureObservableSync.

import { syncState } from "@legendapp/state"
import { configureObservableSync, syncObservable } from "@legendapp/state/sync"
// Change
pluginLocal: ObservablePersistLocalStorage
// To
persist: {
plugin: ObservablePersistLocalStorage
// Change
const { state } = persistObservable(state$, {
local: {
name: "store",
// To
syncObservable(state$, {
persist: {
name: "store",
const state = syncState(state$);

4. Sync

It’s now much easier to sync individual observables with a new plugin system. The Firebase plugin is still in progress, so if you were using that you’ll want to hold off on the upgrade until the full 3.0 release.

See the Persist and Sync docs for the latest.

If you had made a custom sync plugin on the old system, please post an issue on Github or talk to us on Discord, and we will help you with the migration.

5. Removed old sync plugins

Version 2 had inconsistent and varied ways to sync with fetch or Query, and they are now aligned into the Sync system.

Other changes

  • useObservable with a function parameter is now reactive like useComputed was. So use peek() when accessing observables inside it if you want it to be just an initial value and not be reactive.
  • Computeds now only re-compute themselves when observed. This may cause some migration issues if your computeds had side effects, as they will not re-run when dependencies change unless being observed.
  • Removed lockObservable: With the new method of computeds it’s not possible to modify the types to be readonly, so we removed this feature.
  • set and toggle return void: They had previously returned the observable in order to allow chaining, but it caused unintended side effects, so they now return void.
  • onSet was renamed to onAfterSet for clarity
  • Removed the concept of “after batch” - it was generally unreliable because batches can run recursively
  • Renamed enableDirectAccess() to enable$GetSet() and enableDirectPeek() to enable_PeekAssign() for clarity
  • Moved trackHistory export, so you can now use import { trackHistory } from '@legendapp/state/helpers/trackHistory'

1.x to 2.0

Version 2.0 removes old deprecated features to reduce bundle size and encourage everyone to move over to the new features. Version 1.11 displays deprecation warnings to help you migrate.

So there are two migration strategies:

  1. Runtime: Upgrade to version 1.11 and check the console for warnings whenever using deprecated features. This can give you time to do the migration slowly without breaking anything.
  2. Build time: Upgrade to version 2.0 and use TypeScript warnings to find errors

These are all things that were changed over time between 1.0 and 2.0 so depending on when you started using Legend-State you may already be doing it the new way.

Promise behavior changed

When setting a Promise into an observable it creates a state child on the observable with isLoaded and error properties that you can check for load state. After it resolves or rejects it replaces itself with the resolved value and updates the state. Previously in the case of an error it would replace itself with an { error } object.

So if you had logic to check whether a Promise errored by checking the error property on the observable, you can change that to .state.error.

enableLegendStateReact, enableReactDirectRender => Memo

The direct rendering enabled by enableLegendStateReact and enableReactDirectRender was fragile, hard to find in files, and the React team advised against it. So instead we are using the Memo component. See Render an observable directly for more details.

To migrate you can remove usage of enableLegendStateReact() or enableReactDirectRender() as well as any usage of direct rendering, and replace it with Memo. When you remove those imports it will stop overriding the types so rendering observables directly will result in TypeScript errors.

If you were using enableLegendStateReact to render direct observables heavily, enableReactDirectRender is still usable to ease migration, though it will throw TypeScript errors to help you migrate away. It will be fully removed in version 3.0.

// Remove these:
function Component() {
const text$ = useObservable("test");
return (
Change this: {text$}
To this: <Memo>{text$}</Memo>

Legend components changed to Reactive components

The reactive components are now better named and more easily customizable with configuration functions, exported from the normal /react path. See Reactive components for more details.


// React
import { Legend } from "@legendapp/state/react-components";
function Component() {
return <Legend.div>...</Legend.div>;
// React Native
import { Legend } from "@legendapp/state/react-native-components";
function Component() {
return <Legend.View>...</Legend.View>;


// React
import { enableReactComponents } from "@legendapp/state/config/enableReactComponents";
// React Native
import { enableReactNativeComponents } from "@legendapp/state/config/enableReactNativeComponents";
// Now you can use them anywhere
import { Reactive } from "@legendapp/state/react";
function Component() {
// React
return <Reactive.div>...</Reactive.div>;
// React Native
return <Reactive.View>...</Reactive.View>;

For parameter name changed

As we’ve been adopting a convention of naming observables suffixed with $, many users were confused by the item prop in the render component used in For’s item prop, so we renamed it to item$ to make it clear that it’s an observable. item will still work until version 3.0, but it will throw TypeScript errors to encourage changing it to item$.

Reactive props changed to start with $

In an earlier version reactive props ended with $ and were changed in version 1.3.0 to allow starting with $, because it has a better UX with autocomplete and is easier to visually scan for. Both have been supported but version 2.0 will remove type support for the suffix version. It will still work in code so it doesn’t break your apps, but we will fully remove it in 3.0 and suggest you at least start using the new pattern.

A recommended way to find and replace all of instances of the old method is to find $= in all files.

function Component() {
const text$ = useObservable("test");
return (
// Change this
className$={() => "..."}
// to this
$className={() => "..."}

Persistence Changes

In version 2 we locked down and cleaned up the interfaces for the remote persistence APIs.

persistObservable returns an object with sync state

To support taking an initial state or an observable, persistObservable needs to return both an observable and the syncState, so it now the observable with a state property on it, matching the Promise behavior.

See persistObservable for details.

const { state } = persistObservable(initialStateOrObservable, { ... })

persistLocal => pluginLocal

We renamed the parameters for clarity as the difference between local and persistLocal wasn’t clear. So it is now named pluginLocal because that makes more sense.

persistObservable(initialStateOrObservable, {
// Before
persistLocal: ObservablePersistLocalStorage
// After
pluginLocal: ObservablePersistLocalStorage

Remote options renamed

Since there were not any remote persistence plugins before, these changes would likely not affect you unless you made your own. See Remote Persistence for details.

observer, reactive, reactiveObserver not exported from react-components

The /react-components export was mistakenly exporting observer, reactive, and reactiveObserver which are already exported from /react. Your editor may have automatically imported from /react-components so may need to be changed.

// Change this:
import {
} from "@legendapp/state/react-components";
// To this:
import { observer, reactive, reactiveObserver } from "@legendapp/state/react";

types.d.ts moved to types/babel.d.ts

types.d.ts was too generic of a name now that we have a lot of configuration options, so we are naming them more specifically in a “types” folder. For now there’s still only the babel types but this gives room to add more in the future.

// Change this:
/// <reference types="@legendapp/state/types" />
// To this:
/// <reference types="@legendapp/state/types/babel" />

afterBatch removed

afterBatch was not working 100% correctly in all cases, and the best way to fix it was to make it part of batch(...).

// Change
afterBatch(() => {
// To
() => {
() => {

0.23 to 1.0

onChange changed

  1. onChange now takes a second object parameter with trackingType and initial options. If you were using a second parameter (like true to track shallowly) before, use { trackingType: true }.

  2. The onChange callback now receives an object with value, getPrevious, and changes in it, replacing the previous multiple arguments.

These changes allow for more flexibility - it’s easier for callers who care about the changes but not the current value or previous values (like persistence plugins), and the new initial option lets it behave more like observe where it runs immediately instead of waiting for a change.

// Old
obs.onChange((value, getPrevious, changes) => {
// ...
}, true);
// New
({ value, getPrevious, changes }) => {
// ...
{ trackingType: true }

when and Show tweaked

They were previously checking if the value is “ready”, meaning it doesn’t count if it’s an empty object or empty array. They now do a standard javascript truthiness check as would be expected. For the previous behavior you can use whenReady or <Show ifReady={...}>

IndexedDB preloader removed

It was actually slower in our testing so we simplified things and just removed it. See IndexedDB for up-to-date docs.

0.22 to 0.23

Setting an observable object to the same value no longer notifies

Setting an object to itself was triggering notifications, which is not great for performance and is undesirable in most cases. It is now more targeted and will only notify on elements that actually changed. It’s unlikely that will affect you, but it may be a breaking change for you if you depended on things re-computing/re-rendering even if nothing changed.

Not automatically treating DOM nodes and React elements as opaque objects

It was adding most likely unnecessary extra code and is easily solved in a more generic way. If you’re storing those in observables, wrap them in opaqueObject(...).

IndexedDB plugin support for non-dictionaries removed

For flexibility of multiple observables persisting to the same IndexedDB table, it now has an itemID option to save non-dictionaries. So the IndexedDB persistence plugin can be used in two ways:

  1. Persisting a dictionary where each value has an id field, and each value will create a row in the table
  2. Persisting multiple observables to their own rows in the table with the itemID option
const settings = observable({ theme: "light" });
persistObservable(settings, {
local: {
name: "store",
indexedDB: {
itemID: "settings",

0.21 to 0.22

Local Storage is no longer the default persistence

This was changed to reduce build size for those who don’t use it. If you want to use Local Storage, configure it at the beginning of your app:

import { configureObservablePersistence } from "@legendapp/state/persist";
import { ObservablePersistLocalStorage } from "@legendapp/state/local-storage";
persistLocal: ObservablePersistLocalStorage,

Moved persist plugins to /persist-plugins

Update your import paths:

import { ObservablePersistLocalStorage } from "@legendapp/state/persist-plugins/local-storage";
import { ObservablePersistMMKV } from "@legendapp/state/persist-plugins/mmkv";

when is not triggered by empty or []

If you wanted when to be triggered by those, you can update it to use a selector to return a boolean like:

const obs = {}
when(() => !!obs, () => {...})

0.20 to 0.21

Changed onChange callback

The extra paremeters in the onChange callback have changed to include an array of of the changes, fixing a bug where it was only showing the latest child’s change when changing multiple children while batching. This likely won’t affect many of you as it’s mostly intended for internal use and persistence plugins.

Renamed React components from legend to Legend

We had originally used lower casing to match html elements, but in practice it did not autocomplete well and felt wrong. So just rename to uppercase, for example from <legend.div /> to <Legend.div />.

0.19 to 0.20

Removed deprecated automatic observing

The automatic observing from 0.18 was deprecated in 0.19 and is now removed. See Deprecated automatic observing.

observe and useObserve

As observe has gotten more and more powerful, it outgrew modifying behavior based on the return value, so it now has an event parameter to control canceling listening and a cleanup function.

  • If you were returning false to cancel observing, you can now use e.cancel = true.
  • If you were returning a cleanup function you can use e.onCleanup = () => ....
  • It also adds a num param to know how many times it’s run and a previous param to compare to the previous value.
observe((e) => {
// Cancel observing any future changes
e.cancel = true
// A cleanup function
e.cleanup = () => ...

Renamed event dispatch to fire

Just change evt.dispatch() to and all is good 👍.

0.18 to 0.19

Deprecated automatic observing

We are deprecating the automatic observing that depended on hooking into React’s internals. Components will no longer track observables automatically, but you can easily it per component in a few ways:

  • Wrap components in observer to make them track automatically
  • Wrap observable access in useSelector to return a value and track automatically.
  • Render observables directly into JSX.

So tracking observables in React can look like this now:

import { observer } from "@legendapp/state/react";
const Component = observer(function Component() {
const value = observable.get();
// This tracks because it's inside an observer


import { useSelector } from "@legendapp/state/react";
function Component() {
// Track the value of an observable
const value = useSelector(observable);
// Track the return value of a function
const isSelected = useSelector(() => id === state.selected.get());

See the React guide for how we suggest setting up your components now.

Rendering observables directly still works though, and enableLegendStateReact() still enables that.

You can still enable the previous behavior for now with enableLegendStateReact({ autoTrackingDEPRECATED: true }) while you migrate to using observer or useSelector. That option will be removed before we reach 1.0.


  • It doesn’t actually work. We thought this method would be safe to use because it was inspired by Preact Signals, but as we’ve integrated Legend-State into more environments we found significant edge cases that seem to be unfixable and suggest that the whole concept is just unworkable.
  • The React team has asked us not to do it and made it clear that it is likely to break in a future version of React.
  • As Legend-State has evolved, the ideal way of using it has shifted towards fine-grained reactivity where components render minimally or only once, and we were actually specifically opting out of auto-tracking more often than not. So in the interest of pursuing the render-once ideal, we think it’s actually generally better to use the reactivity components or opt-in to tracking.
  • We don’t want to distract from the core mission of Legend-State with an unreliable and unstable core.

Bindable components deprecated

We now have a more general purpose way of making reactive props that can also be used for two-way binding for inputs. So change:

<Bindable.input bind={observable} />


import { Legend } from "@legendapp/state/react-components";
<legend.input value$={observable} />;

See reactive props for more detauls.

value is no longer exposed

Primitives no longer have a value that you could access and modify. We had previously removed that from the documentation and it is now removed from the code. You can just get() and set() as you would any other observable. It turned out to cause more bugs than it was worth and made the TypeScript types overly complex.

Removed get(false)

Use peek() instead.

0.17 to 0.18

The tracing functions are renamed to use* to be inline with hooks:

  • useTraceListeners
  • useTraceUpdates
  • useVerifyNotTracking
  • useVerifyOneRender (new)

0.16 to 0.17

Primitives are now returned as observables

Observables previously tried to be clever by returning primitives directly, which was great in making it easy to work with state directly. But especially as the goal has moved more towards fine-grained reactivity, the balance shifted towards observable objects being better. So accessing primitives through state now returns observables like anything else.

Raw primitives:

  • Pro: Easy to work with
  • Con: Required obs() to get the observable to pass to props or render directly
  • Con: Easy to track a value without realizing it

Observable primitives

  • Pro: More consistent
  • Pro: Easier to deal with undefined
  • Pro: Can dot through undefined paths easily
  • Pro: Doesn’t need obs() or set by key
  • Pro: Easier to use fine-grained features without obs() everywhere
  • Pro: Easier to pass as props without needing obs()
  • Con: Requires get() for primitives

Changes to make:


Wherever you were accessing primitives directly, add a .get() to the end of it.

set(key, value)

Change set by key to access the node first. It will now work fine if the node is undefined.

From: state.profile.set('name', 'Annyong')



Just remove it. The default behavior is now the same as what obs() did before.

Hooks renamed

useComputed is now useSelector, re-rendering only when the return value changes.

useComputed now returns a computed observable.

0.15 to 0.16

enableLegendStateReact() to observe, removed observer

Legend-State now automatically tracks observable access in any component. To set it up, just call enableLegendStateReact() at the beginning of your app.

Now observer is no longer needed, so just remove all usage of observer.

0.14 to 0.15


There are now three levels of safety: Unsafe, Default, and Safe. Default is new and allows direct assignment to primitives but prevents directly assigning to everything else. The previous default behavior was Unsafe so you may see errors if you were directly assigning to objects/arrays/etc… TypeScript should show errors so it should be easy to find them. Replace those with .set(...) or pass in false as the second parameter to observable to go back to “Unsafe” mode.

// 1. Unsafe: Use false for the previous unsafe behavior
const obs = observable({ ... }, /*safe*/ false)
// 2. Default: The new default behavior prevent directly assigning to objects, but allows directly assining to primitives
const obs = observable({ text: 'hello', obj: {} })
obs.text = 'hi'
// ✅ Setting a primitive works in default mode but not in safe mode.
obs.obj = {}
// ❌ Error. Cannot assign to objects directly.
// 3. Safe: Safe mode prevents all direct assignment
const obs = observable({ text: 'hello', obj: {} }, /*safe*/true)
obs.text = 'hi'
// ❌ Error. Cannot assign directly in safe mode.

Renamed ref to obs

ref was a bit unclear and conflicted with React - the new feature to directly render observables requires a ref property. So it is now renamed to obs, which feels more intuitive as it is used to get an observable.

const state$ = observable({ text: "" });
// Before
const textRef = state$.ref("text");
const textRef2 = state$.text.ref();
// Now
const textObs = obs.obs("text");
const textObs2 = obs.text.obs();

Array optimizations

The array optimizations are now opt-in, because they are only useful in React and can potentially have some unexpected behavior in React if modifying the DOM externally. You can enable them by using the For component with the optimized prop. See Arrays for more.

const obs = observable({ items: [] });
const Row = observer(function Row({ item }) {
return <div>{item.text}</div>;
const List = observer(function () {
// The optimized prop enables the optimizations which were previously default
return <For each={list} item={Row} optimized />;


Since there’s now a additionally the optimized tracking for arrays, the shallow option on get() and obs() now has another option. So instead of passing shallow to an observable, use the Tracking namespace now.

import { Tracking } from "@legendapp/state";
const obs = observable([]);
// Before
// Now


The observableBatcher namespace is removed and the batching functions are now exported on their own.

import { batch, beginBatch, endBatch } from '@legendapp/state'
// batch()
batch(() => {

Change functions => observe/when

The new observe and when functions can automatically track all observables accessed while running them. This made the old extra change utilities unnecessary, so onTrue, onHasValue, onEquals, and onChangeShallow have been removed, saving 200 bytes (7%) from the bundle size. These are the new equivalents:

import { observe, when } from "@legendapp/state";
const obs = observable({ value: undefined });
// onTrue
// New onTrue equivalent
when(() => obs.value === true, handler);
// onHasValue
obs.value.onHasValue("text", handler);
// onHasValue equivalent
when(() => obs.value, handler);
// onEquals
obs.value.onEquals("text", handler);
// onEquals equivalent
when(() => obs.value === "text", handler);
// onChangeShallow
// onChangeShallow equivalent
obs.value.onChange(handler, { shallow: true });

Primitive current => value

Primitive observables are now wrapped in { value } instead of { current }. You can also now modify the value directly.

const obs = observable(10);
// Before
obs.current === 10;
obs.curent = 20; // ❌ Error
// Now
obs.value === 10;
obs.value = 20; // ✅ Works

Renamed observableComputed and observableEvent

observableComputed is now just computed and observableEvent is now just event.

import { computed, event } from '@legendapp/state'
// Before
const value = observableComputed(() => ...)
// Now
const value = computed(() => ...)
// Before
const evt = observableEvent(() => ...)
// Now
const evt = event(() => ...)

Renamed LS to Bindable

The automatically bound exports are now named better and in their own exports, so change your exports from LS to:

// Web
import { Bindable } from "@legendapp/state/react-components";
// React Native
import { Bindable } from "@legendapp/state/react-native-components";

Renamed Isolate to Computed

The control flow component Isolate is renamed to Computed for naming consistency.

Removed memo and isolate props

We found these confusing in practice as it wasn’t super clear when a component was getting memoized, and it’s not much extra work to use the Memo and Computed components directly. If you were using those, switch to the Computed and Memo components instead

// Before
<div memo>...</div>
<div computed>...</div>
// Now