Variable: adapt

const adapt: StateAdapt["adapt"]

Defined in: lib/adapt.function.ts:329

adapt wraps StateAdapt.adapt for Angular.

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.

export class MyComponent {
  name = adapt('John');

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

    this.name.set('Johnsh'); // logs 'Johnsh'
    this.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.

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

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

    this.name.concat('sh'); // logs 'Johnsh' and 6
    this.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.

export class MyService {
  tick$ = interval(1000);

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

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

When a store is subscribed to, it passes the subscriptions up to 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

export class MyService {
  nameChange$ = source<string>();

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

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

    this.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

export class MyService {
  nameChange$ = source<string>();
  nameChange2$ = source<string>();

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

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

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

export class MyService {
  nameChange$ = source<string>();
  nameReset$ = source<void>();

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

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

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

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

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

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

The path string specifies the location in the global store you will find the state for the store being created (while the store has subscribers). 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

export class MyComponent {
  store = adapt(0, { path: 'number' });

  constructor() {
    this.store.state$.subscribe();
    // global state: { number: 0 }
  }
}

export class MyComponent {
  store = adapt(0, { path: 'featureA.number' });

  constructor() {
    this.store.state$.subscribe();
    // global state: { featureA: { number: 0 } }
  }
}

export class MyComponent {
  store = adapt(0, { path: 'featureA.featureB.number' });

  constructor() {
    this.store.state$.subscribe();
    // global state: { featureA: { featureB: { number: 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 substrings 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';

export class MyComponent {
  store1 = adapt(0, { path: 'number' + getId() });
  store2 = adapt(0, { path: 'number' + getId() });

  constructor() {
    this.store1.state$.subscribe();
    this.store2.state$.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.

Remember!

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