[Angular] Introduce to NGXS

Went though tow youtube videos about NGXS

• https://angularfirebase.com/lessons/ngxs-quick-start-angular-state-management/
• https://www.youtube.com/watch?v=SfiO3bDUK7Q

The main thing which I am interested about is whether it can achieve the same effect as NGRX.

Haven't quite get fianl answer yet, but it looks very promising.

1. It is simple.

It has the same partten as redux-like tools.

For example, in the component, you can do:

  constructor(private store: Store) {
  }

  addAnimal(name: string) {

    this.store.dispatch(
      // dispatch an action here
    ).subscribe(() => {
      this.name.nativeElement.value = ''; // clean the input field
    });
  }

It return an Observable, so you can subscribe it and do anything house keeping stuff here.

Action creator:

export class AddAnimal {
  static readonly type = '[Zoo] Add Animals';
  constructor(public payload: string) {}
}

Notice here, it is using static function.

But NGXS doesn't have reducer concept, and it doesn't have effect class as well. But I feel this also simply the code a lot. In NGXS, all you need is something called state file:

import {Action, Selector, State, StateContext} from '@ngxs/store';
import {AddAnimal, RemoveAnimal} from './animals.action';
import {ZooService} from './zoo.service';

// Define the state Model interface
export interface ZooStateModel {
  animals: string[];
  loading: boolean;
}

// Define the State
@State<ZooStateModel>({
  name: 'zoo',
  defaults: {
    animals: [],
    loading: false
  }
})
export class ZooState {

  // You are able to use DI in state
  constructor(private zooService: ZooService) {
  }

  // Memory selector, for public access the state
  @Selector()
  static getAllAnimals(state: ZooStateModel) {
    return state.animals;
  }

  @Selector()
  static isLoading( state: ZooStateModel){
    return state.loading;
  }

   // Async action
  @Action(AddAnimal)
  addAnimal({getState, setState, patchState, dispatch}: StateContext<ZooStateModel>, {payload}: AddAnimal) {
    const state = getState();
    setState({
      animals: [...state.animals, payload],
      loading: true
    });
    this.zooService.addAnimal(payload)
      .then(() => {
        patchState({
          loading: false
        });
      })
      .catch((res) => {
        const newState = getState();
        setState({
          animals: newState.animals.filter(name => name !== payload),
          loading: false
        });
      });
  }
}

1. You are able to ui Angular DI inside state file. This is a huge advantage.
2. Actions are no longer sync, it can be async! 
3. We are still able to use Selector, it works as interal(state) to exteral(component) connect. Notice that Selector are also static method

// Inside component you can do:
export class ZooComponent implements OnInit {

  ...

  @Select(ZooState.getAllAnimals) animals$: Observable<any>;
  @Select(ZooState.isLoading) loading$: Observable<boolean>;

  constructor(private store: Store) {
  }

}

　　4. If you need more than one State working together. it is also easy to achieve, just inject Store to constructor().

import {Action, Selector, State} from '@ngxs/store';

interface SelectStateModel {
  id: number;
}

export class SetSelected {
  static readonly type = '[Select] Set Selected';
  constructor(public payload: number) {}
}

@State<SelectStateModel>({
  name: 'selected',
  defaults: {
    id: null
  }
})
export class SelectState {

  @Action(SetSelected)
  setSelected({patchState}, {payload}: SetSelected) {
    patchState({
      id: payload
    });
  }

  @Selector()
  static getSelectedId(state: SelectStateModel) {
    return state.id;
  }
}

export class ZooState {

  constructor(private zooService: ZooService, private store: Store) {
  }

  @Action(AddAnimal)
  addAnimal(name: string) {
     // to get current selectedId from other state
     const currentId$ = this.store.select(SelectState.getSelectedId);
  }

  ...
}