Class: StateAdapt<CommonStore>

Defined in: libs/rxjs/src/lib/global-store/state-adapt.ts:88

Type Parameters

CommonStore

CommonStore extends GlobalStoreMethods = any

Methods

adapt()

adapt<State, S, R, R2, ReturnedSources>(initialState, second): InitializedSmartStore<State, S, object extends R ? R2 : R>

Defined in: libs/rxjs/src/lib/global-store/state-adapt.ts:334

adapt creates a store that will manage state while it has subscribers.

Example: initialState only

adapt(initialState)

The simplest way to use adapt is to only pass it an initial state. adapt returns a store object that is ready to start managing state once it has subscribers. The store object comes with set and reset methods for updating state, and a state$ observable of the store's state.

const name = adapt('John');

name.state$.subscribe(console.log); // logs 'John'

name.set('Johnsh'); // logs 'Johnsh'
name.reset(); // logs 'John'

Usually you won't manually subscribe to state like this, but you can if you want the store to immediately start managing state and never clean it up.

Example: Using an adapter

adapt(initialState, adapter)

You can also pass in a state Adapter object to customize the state change functions and selectors.

const name = adapt('John', {
  concat: (state, payload: string) => state + payload,
  selectors: {
    length: state => state.length,
  },
});

name.state$.subscribe(console.log); // Logs 'John'
name.length$.subscribe(console.log); // Logs 4

name.concat('sh'); // logs 'Johnsh' and 6
name.reset(); // logs 'John' and 4

Example: Using AdaptOptions

adapt(initialState, { adapter, sources, path })

You can also define an adapter, sources, and/or a state path as part of an AdaptOptions object.

Sources allow the store to declaratively react to external events rather than being commanded by imperative code in callback functions.

const tick$ = interval(1000);

const clock = adapt(0, {
  adapter: {
    increment: state => state + 1,
  },
  sources: tick$, // or [tick$], or { set: tick$ }, or { set: [tick$] }
  path: 'clock',
});

clock.state$.subscribe(console.log); // Logs 0, 1, 2, 3, etc.

When a store is subscribed to, it passes the subscriptions up the its sources. For example, if a store has an HTTP source, it will be triggered when the store receives its first subscriber, and it will be canceled when the store loses its last subscriber.

There are 4 possible ways sources can be defined:

1. A source can be a single source or Observable<State>. When the source emits, it triggers the store's set method with the payload.

Example: Single source or observable

const nameChange$ = source<string>();

const name = adapt('John', {
  sources: nameChange$,
  path: 'name',
});

name.state$.subscribe(console.log); // Logs 'John'

nameChange$.next('Johnsh'); // logs 'Johnsh'

2. A source can be an array of sources or Observable<State>. When any of the sources emit, it triggers the store's set method with the payload.

Example: Array of sources or observables

const nameChange$ = source<string>();
const nameChange2$ = source<string>();

const name = adapt('John', {
  sources: [nameChange$, nameChange2$],
  path: 'name',
});

name.state$.subscribe(console.log); // Logs 'John'

nameChange$.next('Johnsh'); // logs 'Johnsh'
nameChange2$.next('Johnsh2'); // logs 'Johnsh2'

3. A source can be an object with keys that match the names of the Adapter state change functions, with a corresponding source or array of sources that trigger the store's reaction with the payload.

Example: Object of sources or observables

const nameChange$ = source<string>();
const nameReset$ = source<void>();

const name = adapt('John', {
  sources: {
    set: nameChange$,
    reset: nameReset$,
  },
  path: 'name',
});

name.state$.subscribe(console.log); // Logs 'John'

nameChange$.next('Johnsh'); // logs 'Johnsh'
nameReset$.next(); // logs 'John'

4. A source can be a function that takes in a detached store (doesn't chain off of sources) and returns any of the above types of sources or observables.

Example: Function that returns an observable

const name = adapt('John', {
  sources: store => store.state$.pipe(
    delay(1000),
    map(name => `${name}sh`),
  ),
  path: 'name',
});

name.state$.subscribe(console.log); // Logs 'John'
// logs 'Johnsh' after 1 second, then 'Johnshsh' after 2 seconds, etc.

Defining a path alongside sources is recommended to enable easier debugging with Redux DevTools. It's easy to trace state changes caused by user events, but it's much harder to trace state changes caused by spontaneous RxJS streams.

The path string specifies the location in the global store you will find the state for the store (while it is being used). StateAdapt splits this string at periods '.' to create an object path within the global store. Here are some example paths and the resulting global state objects:

Example: Paths and global state

const count1 = adapt(0, { path: 'count.1' });
const count2 = adapt(0, { path: 'count.2' });

this.count1.state$.subscribe();
// global state:
// {
//   count: {
//     1: 0,
//   }
// }

this.count2.state$.subscribe();
// global state:
// {
//   count: {
//     1: 0,
//     2: 0,
//   }
// }

Each store completely owns its own state. If more than one store tries to use the same path, StateAdapt will throw this error:

Path '${path}' collides with '${existingPath}', which has already been initialized as a state path.

This applies both to paths that are identical as well as paths that are subtrings of each other. For example, if 'featureA' is already being used by a store and then another store tried to initialize at 'featureA.number', that error would be thrown.

To help avoid this error, StateAdapt provides a getId function that can be used to generate unique paths:

Example: getId for unique paths

import { getId } from '@state-adapt/core';

const store1 = adapt(0, { path: 'number' + getId() });
store1.state$.subscribe();
const store2 = adapt(0, { path: 'number' + getId() });
store2.state$.subscribe();
// global state includes both: { number0: 0, number1: 0 }

No path

If no path is provided, then the store's path defaults to the result of calling getId.

Example: Initial state factory

adapt(() => initialState)

You can pass a function that returns the initial state. The store calls it when it activates, keeps that value for as long as it stays active, and discards it when it deactivates — so the factory runs again for each activation.

This helps when initial state might be different at each time the store is being used, like with localStorage:

const name = adapt(() => localStorage.getItem('name') ?? 'John');

// `localStorage` hasn't been read yet

const sub1 = name.state$.subscribe(console.log); // Reads `localStorage`, then logs 'John'
name.set('Johnsh'); // logs 'Johnsh'
name.reset(); // logs 'John'
sub1.unsubscribe(); // The store deactivates and forgets 'John'

localStorage.setItem('name', 'Jane');

const sub2 = name.state$.subscribe(console.log); // Reads `localStorage` again, logs 'Jane'
name.set('Janesh'); // logs 'Janesh'
name.reset(); // logs 'Jane', not 'John'

A one-off store read will call the state factory function.

Remember!

The store needs to have subscribers in order to start managing state, and it only subscribes to sources when it has subscribers itself.

Type Parameters

State

State

S

S extends Selectors<State>

R

R extends ReactionsWithSelectors<State, S>

R2

R2 extends ReactionsWithSelectors<State, S>

ReturnedSources

ReturnedSources = unknown

Parameters

initialState

InitialState<State>

second

R & object & NotAdaptOptions | AdaptOptions<State, S, R2, ReturnedSources>

Returns

InitializedSmartStore<State, S, object extends R ? R2 : R>

---

watch()

watch<State, S, R>(path, adapter?): SmartStore<State, S & WithGetState<State>>

Defined in: libs/rxjs/src/lib/global-store/state-adapt.ts:474

watch returns a detached store (doesn't chain off of sources). This allows you to watch state without affecting anything. It takes the path of the state you are interested in and, optionally, the adapter whose selectors you want to use.

watch(path, adapter)

path — Object path in Redux Devtools

adapter — Optional object with state change functions and selectors. When omitted, watch uses the base adapter.

Usage

watch enables accessing state without subscribing to sources. For example, if your adapter manages the loading state for an HTTP request and you need to know if the request is loading before the user is interested in the data, watch can give you access to it without triggering the request.

Example: Accessing loading state

watch('data', httpAdapter).loading$.subscribe(console.log);

Type Parameters

State

State = any

S

S extends Selectors<State> = { }

R

R extends ReactionsWithSelectors<State, S> = { }

Parameters

path

string

adapter?

Adapter<State, S, R & BasicAdapterMethods<State>>

Returns

SmartStore<State, S & WithGetState<State>>