Here is my Interface ISomeModel

export interface ISomeModel {
  id?: string;
  title: string;
  description: string;
  // .... other fields
}

Here is my class SomeService

class SomeService {
  static fromJsonAndId(json: any, id?: string): ISomeModel {
    return {
      id: id,
      title: json.title,
      description: json.description,
      // ..... other fields
    } as ISomeModel;
  }

  handleFirestoreError(error: any) {
    if (error.code === 'permission-denied' || error.code === 'unauthenticated') {
      tokenService.logout(true);
    } else {
      throw error;
    }
  }

  create(someModel: ISomeModel): Promise<ISomeModel | void> {
    return db
      .add(someModel)
      .then((doc) => SomeService.fromJsonAndId(someModel, doc.id))
      .catch((err) => this.handleFirestoreError(err));
  }

}

export default new SomeService();

Here is my react component where I am using the create method:

const someInstance = await someService.create(someModelObj);
console.log('created', someInstance.id);

But I get this error in my ide(webstorm):

The create function would either return ISomeModel instance or throw error. It can never return void. So why am I getting that error? And how do I fix it?

CodePudding user response：

const someInstance = await someService.create(someModelObj) as ISomeModel

or maybe you can use a typeof to detect is a void or a ISomeModel

CodePudding user response：

Here you can explicitly tell TypeScript that when an error is being handled, you return a null value. So you can either have an object with type definition of ISomeModel or a null value (Here you can use optional chaining operator - ? to make sure you're only accessing the object if it exists). The code will look like below (I have mocked some objects like db and tokenService) :-

export interface ISomeModel {
  id?: string;
  title: string;
  description: string;
  // .... other fields
}

type Nullable<T> = T | null;

const db = {
    add:(someModel:ISomeModel)=>Promise.resolve({id:'sd',title:'df',description:'fdf'})
}

const tokenService = {
    logout:(someboolean:boolean)=>{}
}

class SomeService {
  static fromJsonAndId(json: any, id?: string): ISomeModel {
    return {
      id: id,
      title: json.title,
      description: json.description,
      // ..... other fields
    } as ISomeModel;
  }

  handleFirestoreError(error: any) {
    if (error.code === 'permission-denied' || error.code === 'unauthenticated') {
        tokenService.logout(true);
        return null;
    } else {
      throw error;
    }
  }

  create(someModel: ISomeModel): Promise<Nullable<ISomeModel>> {
    return db
      .add(someModel)
      .then((doc:any) => SomeService.fromJsonAndId(someModel, doc.id))
      .catch((err:any) => this.handleFirestoreError(err));
  }

}

export default new SomeService();

const someService = new SomeService();
try{
const someInstance = await someService.create({  id: '3434343',
  title: 'Some object title',
  description: 'some object description'});
console.log('created', someInstance?.id);
}
catch(err:any){
    // handle other errors
}

Also here is the typescript playground