WORKING WITH STATE MACHINES IN ANGULAR

@stefanos_lig

  • WHAT IS XSTATE, STATE MACHINES & STATECHARTS
  • HOW TO  CREATE/USE THEM WITH ANGULAR
 
  • WHEN TO USE THEM
 
  • WHY THIS PRESENTATION
  • TAKEAWAY
 

@stefanos_lig

  • WHAT IS XSTATE, STATE MACHINES & STATECHARTS
  • HOW TO  CREATE/USE THEM WITH ANGULAR
 
  • WHEN TO USE THEM
 

Agenda

  • WHY THIS PRESENTATION
  • TAKEAWAY
 

The Journey to state machines

@stefanos_lig

It might be the software entropy

@stefanos_lig

The Journey to state machines

Out of the tar pit

The Journey to state machines

@stefanos_lig

What is the complexity of a system?

The Journey to state machines

@stefanos_lig

Lack of understanding

What we try to do most of the time is to read the source code and understand it

What is the complexity of a system?

The Journey to state machines

@stefanos_lig

State

Control

Lack of understanding

What we try to do most of the time is to read the source code and understand it

The Journey to state machines

@stefanos_lig

State

Control

What is the complexity of a system?

The Journey to state machines

@stefanos_lig

Lack of understanding

What we try to do most of the time is to read the source code and understand it

In a team, we want all the participants to be able to speak the same language

XState

@stefanos_lig

The Journey to state machines

THE JOURNEY TO STATE MACHINES

@stefanos_lig

Lack of understanding

In a team, we want all the participants to be able to speak the same language

Stefanos Lignos

Front-end developer

@stefanos_lig

github.com/stefanoslig

http://stefanos-lignos.com/

@stefanos_lig

Angular Athens

  • WHAT IS XSTATE, STATE MACHINES & STATECHARTS
  • HOW TO  CREATE/USE THEM WITH ANGULAR
 
  • WHEN TO USE THEM
 
  • WHY THIS PRESENTATION
  • TAKEAWAY
 

@stefanos_lig

  • WHAT IS XSTATE, STATE MACHINES & STATECHARTS
  • HOW TO  CREATE/USE THEM WITH ANGULAR
 
  • WHEN TO USE THEM
 
  • WHY THIS PRESENTATION

Agenda

Disclaimer: This is not a detailed explanation of XState, but a presentation about something that you might find useful/inspiring to apply in your project!
  • TAKEAWAY
 

A library for creating finite state machines and statecharts

 

Xstate

 

@stefanos_lig

What is

@stefanos_lig

What is

 A FINITE STate machine

The life of a programmer as a finite state machine

  • David Harel - 1982
  • Created the language for statecharts
  • A common language for all the engineers in Israel Aircraft Industries
  • SCXML (State Chart XML)
  • Finite State Machines extended with the notions of orthogonality and hierarchy

@stefanos_lig

What is

 A statechart

@stefanos_lig

What is

 A FINITE STate machine

The life of a programmer as a finite state machine

What is

 A statechart

@stefanos_lig

Hierarchy
Orthogonality

The life of a programmer as a statechart 

Guarded Transitions
History nodes
Delayed events & transitions
  • WHAT IS XSTATE, STATE MACHINES & STATECHARTS
  • HOW TO  CREATE/USE THEM WITH ANGULAR
 
  • WHEN TO USE THEM
 
  • WHY THIS PRESENTATION
  • TAKEAWAY
 

@stefanos_lig

  • WHAT IS XSTATE, STATE MACHINES & STATECHARTS
  • HOW TO  CREATE/USE THEM WITH ANGULAR
 
  • WHEN TO USE THEM
 
  • WHY THIS PRESENTATION

Agenda

  • TAKEAWAY
 
 
authMachine(state, event) {
  if (state === 'unauthorized') {
    if (event.type === 'SIGNIN') {
      return 'signing_in';
    }
  } else if (state === 'authorized') {
    if (event.type === 'LOGOUT') {
      return 'unauthorized';
    }
  } else if (state === 'signing_in') {
    if (event.type === 'SIGNIN_SUCCESS') {
      return 'authorized';
    }
    if (event.type === 'SIGNIN_FAILURE') {
      return 'unauthorized';
    }
  }
}

transition(state, event) {
  this.state$.next({
    value: this.authMachine(state, event),
  });
}

state$ = new BehaviorSubject<State>({
  value: 'unauthorized',
});

How WE CAN CREATE A FINITE STATE MACHINE

@stefanos_lig

A state machine for an authentication process

How WE CAN CREATE A STATE MACHINE

authMachine = {
  states: {
    unauthorized: {
      on: {
        SIGNIN: 'signin',
      },
    },
    authorized: {
      on: {
        LOGOUT: 'unauthorized',
      },
    },
    signing_in: {
      on: {
        SIGNIN_SUCCESS: 'authorized',
        SIGNIN_FAILURE: 'unauthorized',
      },
    },
  },
};

transition(state, event) {
  const nextState = this.authMachine[state].on[event];
  this.state$.next({
    value: nextState,
  });
}

state$ = new BehaviorSubject<State>({
  value: 'unauthorized',
});

@stefanos_lig

A state machine for an authentication process

How WE CAN CREATE A STATE MACHINE

A state machine for an authentication process

@stefanos_lig

@stefanos_lig

Demo

CREATE A STATE MACHINE WITH XSTATE

A state machine for an authentication process

stefanoslig/angular-xstate-nx-realworld-example-app

gothinkster/realworld

@stefanos_lig

private authMachine = Machine<
    AuthMachineContext,
    AuthMachineSchema,
    AuthMachineEvent
  >(
    {
      id: 'auth',
      initial: 'unauthorized',
      states: {
        unauthorized: {},
        signing_in: {},
        signing_up: {},
        authorized: {},
        updating: {},
      },
    },
  1. Define the states

Visualization

CREATE A STATE MACHINE WITH XSTATE

@stefanos_lig

private authMachine = Machine<
    AuthMachineContext,
    AuthMachineSchema,
    AuthMachineEvent
  >(
    {
      id: 'auth',
      initial: 'unauthorized',
      states: {
        unauthorized: {
          on: {
            SIGNIN: 'signing_in',
            SIGNUP: 'signing_up',
          },
        },
        signing_in: {},
        signing_up: {},
        authorized: {
          on: {
            UPDATE_USER: 'updating',
            LOGOUT: { target: 'unauthorized' },
          },
        },
        updating: {},
      },
    },
  1. Define the states
  2. Create the events for the transitions

Visualization

CREATE A STATE MACHINE WITH XSTATE

@stefanos_lig

private ɵauthMachine = Machine<
    AuthMachineContext,
    AuthMachineSchema,
    AuthMachineEvent
  >(
    {
      id: 'auth',
      initial: 'unauthorized',
      states: {
        unauthorized: {
          on: {
            SIGNIN: 'signin',
            SIGNUP: 'signup',
          },
        },
        signin: {
          invoke: { src: 'signIn' },
          on: {
            SIGNIN_SUCCESS: { target: 'authorized' },
            SIGNIN_FAILURE: { target: 'unauthorized' },
          },
        },
        signup: {
          invoke: { src: 'signUp' },
          on: {
            SIGNUP_SUCCESS: { target: 'authorized' },
            SIGNUP_FAILURE: { target: 'unauthorized' },
          },
        },
        authorized: {
          on: {
            UPDATE_USER: 'updating',
            LOGOUT: { target: 'unauthorized' },
          },
        },
        updating: {},
      },
      {
      services: {
        signIn: (_, event: SignIn) =>
          this.authService
            .login({ email: event.username, password: event.password })
            .pipe(
              map((user) => SignInSuccess(user)),
              catchError((result) => of(SignInFail(result.error.errors)))
            ),
        signUp: (_, event: SignUp) =>
          this.authService
            .register({
              username: event.username,
              email: event.email,
              password: event.password,
            })
            .pipe(
              map((user) => SignUpSuccess(user)),
              catchError((result) => of(SignUpFail(result.error.errors)))
            ),
      },
    },
  1. Define the states
  2. Define the events for the unauthorized state
  3. Define the effects

Visualization

CREATE A STATE MACHINE WITH XSTATE

@stefanos_lig

CREATE A STATE MACHINE WITH XSTATE

Extended state/context: Data that can be potentially infinite

@stefanos_lig

private ɵauthMachine = Machine<
    AuthMachineContext,
    AuthMachineSchema,
    AuthMachineEvent
  >(
    {
      id: 'auth',
      initial: 'unauthorized',
      context: {
        user: {
          email: '',
          token: '',
          username: '',
          bio: '',
          image: '',
        },
        errors: [],
      },
      states: {
        unauthorized: {
          on: {
            SIGNIN: 'signin',
            SIGNUP: 'signup',
          },
        },
        signin: {
          invoke: { src: 'signIn' },
          on: {
            SIGNIN_SUCCESS: { target: 'authorized' },
            SIGNIN_FAILURE: { target: 'unauthorized' },
          },
        },
        signup: {
          invoke: { src: 'signUp' },
          on: {
            SIGNUP_SUCCESS: { target: 'authorized' },
            SIGNUP_FAILURE: { target: 'unauthorized' },
          },
        },
        authorized: {
          on: {
            UPDATE_USER: 'updating',
            LOGOUT: { target: 'unauthorized' },
          },
        },
        updating: {},
      },
    },
  1. Define the states
  2. Define the events for the unauthorized state
  3. Define the effects
  4. Define the context

CREATE A STATE MACHINE WITH XSTATE

@stefanos_lig

private ɵauthMachine = Machine<
    AuthMachineContext,
    AuthMachineSchema,
    AuthMachineEvent
  >(
    {
      id: 'auth',
      initial: 'unauthorized',
      context: {
        user: {
          email: '',
          token: '',
          username: '',
          bio: '',
          image: '',
        },
        errors: [],
      },
      states: {
        unauthorized: {
          on: {
            SIGNIN: 'signin',
            SIGNUP: 'signup',
          },
        },
        signin: {
          invoke: { src: 'signIn' },
          on: {
            SIGNIN_SUCCESS: { target: 'authorized', actions: 'assignUser' },
            SIGNIN_FAILURE: { target: 'unauthorized', actions: 'assignErrors' },
          },
        },
        signup: {
          invoke: { src: 'signUp' },
          on: {
            SIGNUP_SUCCESS: { target: 'authorized', actions: 'assignUser' },
            SIGNUP_FAILURE: { target: 'unauthorized', actions: 'assignErrors' },
          },
        },
        authorized: {
          on: {
            UPDATE_USER: 'updating',
            LOGOUT: { target: 'unauthorized', actions: 'logout' },
          },
        },
        updating: {},
      },
      {
      actions: {
        resetUser: assign<AuthMachineContext, AuthMachineEvent>(() => ({
          user: initialContext.user,
        })),
        resetErrors: assign<AuthMachineContext, AuthMachineEvent>(() => ({
          errors: initialContext.errors,
        })),
        goToHomePage: (ctx: AuthMachineContext, event: AuthMachineEvent) =>
          this.router.navigateByUrl(''),
        assignUser: assign<AuthMachineContext, AuthMachineEvent>(
          (ctx, event) => ({
            user: (event as SignInSuccess).response.user,
          })
        ),
        assignErrors: assign<AuthMachineContext, AuthMachineEvent>(
          (_, event) => {
            const eventErrors = (event as SignInFail).errors;
            return {
              errors: Object.keys(eventErrors || {}).map(
                (key) => `${key} ${eventErrors[key]}`
              ),
            };
          }
        ),
        logout: () => {
          localStorage.setItem('authState', null);
          this.router.navigateByUrl('login');
        },
      },
      services: {
        signIn: (_, event: SignIn) =>
          this.authService
            .login({ email: event.username, password: event.password })
            .pipe(
              map((user) => new SignInSuccess(user)),
              catchError((result) => of(new SignInFail(result.error.errors)))
            ),
        signUp: (_, event: SignUp) =>
          this.authService
            .register({
              username: event.username,
              email: event.email,
              password: event.password,
            })
            .pipe(
              map((user) => new SignUpSuccess(user)),
              catchError((result) => of(new SignUpFail(result.error.errors)))
            ),
      },
    },
  1. Define the states
  2. Define the events for the unauthorized state
  3. Define the invoked effects
  4. Define the context
  5. Define the fire & forget effects

CREATE A STATE MACHINE WITH XSTATE

@stefanos_lig

private ɵauthMachine = Machine<
    AuthMachineContext,
    AuthMachineSchema,
    AuthMachineEvent
  >(
    {
      id: 'auth',
      initial: 'unauthorized',
      context: {
        user: {
          email: '',
          token: '',
          username: '',
          bio: '',
          image: '',
        },
        errors: [],
      },
      states: {
        unauthorized: {
          on: {
            SIGNIN: 'signin',
            SIGNUP: 'signup',
          },
        },
        signin: {
          entry: 'resetErrors',
          invoke: { src: 'signIn' },
          on: {
            SIGNIN_SUCCESS: { target: 'authorized', actions: 'assignUser' },
            SIGNIN_FAILURE: { target: 'unauthorized', actions: 'assignErrors' },
          },
        },
        signup: {
          entry: 'resetErrors',
          invoke: { src: 'signUp' },
          on: {
            SIGNUP_SUCCESS: { target: 'authorized', actions: 'assignUser' },
            SIGNUP_FAILURE: { target: 'unauthorized', actions: 'assignErrors' },
          },
        },
        authorized: {
          on: {
            UPDATE_USER: 'updating',
            LOGOUT: { target: 'unauthorized', actions: 'logout' },
          },
        },
        updating: {},
      },
    },
  1. Define the states
  2. Define the events for the unauthorized state
  3. Define the effects
  4. Define the context
  5. Define the fire & forget effects

Visualization

CREATE A STATE MACHINE WITH XSTATE

xstate & angular

import { Machine, interpret } from 'xstate';
import { from } from 'rxjs';

const machine = Machine(/* ... */);
const service = interpret(machine).start();

const state$ = from(service);

state$.subscribe(state => {
  // ...
});

A stateless, enriched version of the FSM configuration 

A stateful, subscribable instance of the FSM 

xstate & angular

(Example)

We defined our machine...the next step is to create a service and start listening to changes in the machine

rehydratedState = JSON.parse(localStorage.getItem('authState'));

authMachine = useMachine(this.ɵauthMachine, {
  devTools: !environment.production,
  state: this.rehydratedState,
  persist: { key: 'authState' },
});

@stefanos_lig

xstate & angular

(Example)

import {
  EventObject,
  StateConfig,
  MachineOptions,
  interpret,
  State,
  InterpreterOptions,
  Interpreter,
  StateMachine,
  Typestate,
  StateSchema,
} from 'xstate';
import { filter, shareReplay, finalize, tap } from 'rxjs/operators';
import { Observable, from, BehaviorSubject, Subject } from 'rxjs';

export type InterpretedService<
  TContext,
  TStateSchema extends StateSchema = any,
  TEvent extends EventObject = EventObject,
  TTypestate extends Typestate<TContext> = any
> = {
  state$: Observable<State<TContext, TEvent>>;
  send: Interpreter<TContext, TStateSchema, TEvent, TTypestate>['send'];
  service: Interpreter<TContext, TStateSchema, TEvent, TTypestate>;
};

export interface UseMachineOptions<TContext, TEvent extends EventObject> {
  /**
   * If provided, will be merged with machine's `context`.
   */
  context?: Partial<TContext>;
  /**
   * The state to rehydrate the machine to. The machine will
   * start at this state instead of its `initialState`.
   */
  state?: StateConfig<TContext, TEvent>;
}

export function useMachine<
  TContext,
  TStateSchema extends StateSchema = any,
  TEvent extends EventObject = EventObject,
  TTypestate extends Typestate<TContext> = any
>(
  machine: StateMachine<TContext, TStateSchema, TEvent>,
  options: Partial<InterpreterOptions> &
    Partial<UseMachineOptions<TContext, TEvent>> &
    Partial<MachineOptions<TContext, TEvent>> = {}
): InterpretedService<TContext, TStateSchema, TEvent, TTypestate> {
  const {
    context,
    guards,
    actions,
    activities,
    services,
    delays,
    persist,
    state,
    ...interpreterOptions
  } = options;

  const machineConfig = {
    context,
    guards,
    actions,
    activities,
    services,
    delays,
  };

  const createdMachine = machine.withConfig(machineConfig, {
    ...machine.context,
    ...context,
  } as TContext);

  const service = interpret(createdMachine, interpreterOptions).start(
    state ? State.create(state) : undefined
  );

  if (!!persist && persist.key) {
    const state$ = from(service).pipe(
      tap((state) => localStorage.setItem(persist.key, JSON.stringify(state))),
      shareReplay(1)
    );
    return { state$, send: service.send, service };
  }

  const state$ = from(service).pipe(
    filter(({ changed }) => changed),
    shareReplay(1)
  );

  return { state$, send: service.send, service };
}

export function useService<
  TContext,
  TStateSchema extends StateSchema = any,
  TEvent extends EventObject = EventObject,
  TTypestate extends Typestate<TContext> = any
>(
  service: Interpreter<TContext, TStateSchema, TEvent, TTypestate>
): InterpretedService<TContext, TStateSchema, TEvent, TTypestate> {
  const state$ = from(service).pipe(
    shareReplay(1),
    finalize(() => service.stop())
  );

  return { state$, send: service.send, service };
}

@stefanos_lig

  • Interpret the machine we have created
  • Get an observable from the service

Testing

@stefanos_lig

  • WHAT IS XSTATE, STATE MACHINES & STATECHARTS
  • HOW TO  CREATE/USE THEM WITH ANGULAR
 
  • WHEN TO USE THEM
 
  • WHY THIS PRESENTATION

Agenda

  • TAKEAWAY
 

Why I should start Using xstate?

@stefanos_lig

But...you can ask yourself

@stefanos_lig

  1. Is the business logic embedded/spread across your components/templates?
  • One source of truth for the business logic/behavior
  • Framework agnostic - the backbone of your app can be migrated immediately to another framework
  • The business logic/behavior is decoupled from the components - easier to be tested
  • Readability
  • Easier to extend the current functionality

With XState:

But...you can ask yourself

@stefanos_lig

  • Everyone can understand the visualization of the state machines
  • Less back and forth communication between BA & devs
  • Can be a useful documentation

With XState:

2. Do I have a common language in my team?

3. Do I need documentation for the business logic?

But...you can ask yourself

@stefanos_lig

  • It forces us to think about the solution to a problem upfront
  • It prevents edge cases - edge cases more visible

 

With XState:

4. Is my codebase unpredictable and buggy?

  • WHAT IS XSTATE, STATE MACHINES & STATECHARTS
  • HOW TO  CREATE/USE THEM WITH ANGULAR
 
  • WHEN TO USE THEM
 
  • WHY THIS PRESENTATION
  • TAKEAWAY
 

@stefanos_lig

  • WHAT IS XSTATE, STATE MACHINES & STATECHARTS
  • HOW TO  CREATE/USE THEM WITH ANGULAR
 
  • WHEN TO USE THEM
 
  • WHY THIS PRESENTATION

Agenda

  • TAKEAWAY
 

My dream

@stefanos_lig

Thank you ♡

Useful links:

StateCharts !== REDUX