ts-dwx-19.pdf

Transcript

1. TypeScript Conditional Types co-IT.eu GmbH Inspire To Change
2. Dynamic types add a lot of flexibility...
3. ... but can become a maintenance nightmare
4. Static types bring order to the dynamic world.
5. Gregor Woiwode medium.com/@gregor.woiwode twitter.com/@GregOnNet Developer, Trainer & Speaker
6. Agenda Syntax Debugging „Error Handling“ Real World Use Case infer nested types *Automated Testing
7. HANDS ON Introducing Conditional Types https://github.com/GregOnNet/conditional-types-playground
8. Conditional types add ternery expressions I N T R O D U C T I O N declare type StringOrNull<T> = T extends string ? string : null;
9. Benefit I N T R O D U C T I O N More flexible type system Better to maintain
10. How to read the syntax I N T R O D U C T I O N declare type StringOrNull<T> = T extends string ? string : null; I f t h e g i v e n t y p e T i s a s t r i n g . . . . . . t h a n re t u r n t h e t y p e s t r i n g . . . o t h e r w i s e re t u r n t h e t y p e n u l l .
11. How to inspect conditional types D E B U G G I N G Since we add logic specifying types more precisely, we need to test it.
12. Fill in the gaps D E B U G G I N G declare type StringOrNull<T> = T extends !... declare type isString = StringOrNull<string>;
13. HANDS ON Manual Debugging
14. Observation D E B U G G I N G declare type isString = StringOrNull<string | number>; type isStringOrNumber = string | null #
15. Learning D E B U G G I N G $ Unwanted types need to be omitted explicitly.
16. Nested ternary expressions CO N D I T I O N A L T Y P E S declare type StringOrNull<T> = T extends string ? string : T extends null ? null : never; . . . o t h e r w i s e i f T i s o f t y p e n u l l . . . r e t u r n t y p e n u l l . . . o t h e r w i s e re t u r n t y p e n ev e r
17. Error handling for types N E V E R T Y P E % The never type represents the type of values that never occur. https://www.typescriptlang.org/docs/handbook/basic-types.html
18. Examples N E V E R T Y P E function error( message: string ): never { throw new Error(message); } function infiniteLoop(): never { while (true) { } } Th rowi n g Error s I n fi n i t e Loop
19. HANDS ON Apply fix
20. Congratulations! C O N D I T I O N A L T Y P E S Now, you are familiar with the syntax of conditional types. Now, we will have a look to apply this knowledge in practice.
21. You can’t see in anyone... Really?
22. Look inside structures inferring types C O N D I T I O N A L T Y P E S type Foo<T> = T extends { a: infer U } ? U : never; I f t h e g i v e n t y p e T h a s t h e p r o p e r t y a n o t i c e i s t t y p e a n d r e t u r n i t .
23. Yet another story about Redux
24. No Redux knowledge needed D I S C L A I M E R No worries, we will continue focusing on conditional types.
25. No Redux bashing D I S C L A I M E R We just have a look at what can be improved. This talk will not mention all the cool benefits coming with Redux.
26. Before centralized state management... I N F E R T Y P E S CO N D I T I O N A L LY export class RootComponent { notes$: Observable<Notes[]>; constructor(private notes: NotesService) { this.notes$ = this.notes.loadNotes(); } }
27. Interacting with the Store is hard I N F E R T Y P E S C O N D I T I O N A L L Y export class RootComponent implements OnInit { constructor(private store: Store<fromNotes.NotesState>) {} ngOnInit() { this.store.dispatch(new LoadNotes()); } } From where do I need to import the state? From where do I need to import the action? Why am I not receiving a return value?
28. Actions need to be maintained I N F E R T Y P E S C O N D I T I O N A L L Y export class LoadNotes implements Action { readonly type = NotesActionTypes.LoadNotes; } export class LoadNotesSuccess implements Action { readonly type = NotesActionTypes.LoadNotesSuccess; constructor(public payload: Note[]) {} }
29. An action is process by a reducer function I N F E R T Y P E S CO N D I T I O N A L LY switch (action.type) { case NotesActionTypes.LoadNotesSuccess: return setNotes(action.payload, slice); !!... function setNotes(notes: Note[], slice: NotesSlice): NotesSlice { return { !!...slice, entities: notes }; } Case Reducer
30. Wouldn‘t it be nice, if ...? I N F E R T Y P E S C O N D I T I O N A L L Y export class RootComponent implements OnInit { notes$: Observable<Note[]>; constructor(private notesFacade: StoreFacade) { this.notes$ = this.notesFacade.all$; } ngOnInit() { this.notesFacade.loadNotes(); } } Creates Action + Dispatches Action Is created dynamically Offers consumable selectors
31. What needs to be done? I N F E R T Y P E S C O N D I T I O N A L L Y Action Type Case Reducer Self Dispatching Action (payload: P) => void | () => void Case Reducer
32. Low hanging fruit | Automating reducer generation I N F E R T Y P E S C O N D I T I O N A L L Y Self Dispatching Action Self Dispatching Action Self Dispatching Action Self Dispatching Action Reducer C o m b i n i n g a ct i o n t y p e & c a s e re d uc e r b u i l d i n g t h e red u cer fu n ct i o n .
33. The case reducer challange I N F E R T Y P E S CO N D I T I O N A L LY function caseReducerA<T, P>(state: T, payload: P): T { !!... } function caseReducerB<T, Q>(state: T, payload: Q): T { !!... } function caseReducerC<T>(state: T): T { !!... } Or ... Or ...
34. Self dispatching action I N F E R T Y P E S C O N D I T I O N A L L Y Type Case Reducer
35. HANDS ON Getting to know infer https://github.com/GregOnNet/conditional-types-playground
36. Learning I N F E R T extends (state: any, payload: infer TPayload) !=> any ? (payload: TPayload) !=> void : never; i n f e r l e t s y o u ex t ra c t a t y p e b a s e d o n t h e u s a g e o f t h e re s p e c t i v e m e t h o d
37. Congratulations! C O N D I T I O N A L T Y P E S Now, you can handle more advanced challenges using conditional types.
38. NgRx Ducks C O N D I T I O N A L T Y P E S @Ducksify({ initialState: !!... }) export class NoteDucks { loadAll = effect('Load Notes‘); @Action('Loading Notes succeeded') set(State: State, notes: Note[]) { return { !!...state, entities: notes }; } Case Reducer Type @Component({ !!... }) export class RootComponent implements OnInit { constructor(@Inject(NoteDucks) private ducks: Duck<NoteDucks>) {} ngOnInit() { this.ducks.loadAll.dispatch(); } }
39. https://npmjs.org/@co-it/ngrx-ducks
40. Predefined helper types I N F E R T Y P E S CO N D I T I O N A L LY Exclude<T, U> Exclude from T those types that are assignable to U. Extract<T, U> Extract from T those types that are assignable to U. NonNullable<T> Exclude null and undefined from T. ReturnType<T> Obtain the return type of a function type. InstanceType<T> Obtain the instance type of a constructor function type. ConstructorParameters<T> Obtain the parameter types of a constructor function type. https://www.typescriptlang.org/docs/handbook/advanced-types.html
41. Recapitulation THE END Conditional Types are ternary expressions Conditional Types can be nested Nested types can be extracted with infer Conditional Types add more flexibility Automated tests can be done with ts-snippet
42. medium.com/@gregor.woiwode @GregOnNet co-IT.eu GmbH Inspire to change Thank you for listening. http://speakerdeck.com/gregonnet/ts-dwx-19
43. Further Reading R E S O U R C E S Conditional types in TypeScript - Artsy Engineering TypeScript 2.8: Conditional Types — Marius Schulz Notes on TypeScript: Conditional Types - DEV Community *+ Conditional types in TypeScript – JavaScript everyday – Medium TypeScript: Create a condition-based subset types – DailyJS – Medium A Look at TypeScript’s Conditional Types TypeScript conditional types real-life example - codewithstyle.info https://www.reddit.com/r/typescript/comments/9n189u/how_are_you_using_conditional_types/