CODEWITHSUNDEEP
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Capan
Capan

Reputation: 756

Typescript This expression is not constructable. error on inherited class structure

I'm trying to personalize my error classes inside the application.

I have totally four classes; Exception, GenericError, BaseService, CarService two main and two inherited. GenericError extends ExceptionClass and CarService extends BaseService. I'm not be able to change constructor property of GenericError class. I'm getting this error;

This expression is not constructable.

TS Snippet

What is wrong with my class inheritence logic?

// Exception.ts
class ExceptionClass extends Error {
  status: number;
  message: string;
  errors?: object;
  constructor(status: number, message: string, errors?: object) {
    super(message);
    this.status = status;
    this.message = message;
    this.errors = errors;
  }
}

// GenericError.ts
class GenericException extends ExceptionClass {
  constructor(message?: string) {
    super(400, message || 'Internal Error');
  }
}

// BaseService.ts
class BaseService {
  genericError: GenericException;

  constructor(message: string) {
    this.genericError = new GenericException();
  }
}

// CarService.ts
export default class CarService extends BaseService {
  constructor() {
        super('')
        console.log("CarService started!");
    }
  async checkCar() {
    return new Promise(async (resolve: any, reject: any) => {
      //** Imagine some business logic that fails */
      const passwordsNotMatchErr = new this.genericError('Fail Reason bla bla');
      return reject(passwordsNotMatchErr);
    })
  }
}

Upvotes: 1

Views: 4468

Answers (1)

Cesar
Cesar

Reputation: 447

The problem is that in the following line:

const passwordsNotMatchErr = new this.genericError('Fail Reason bla bla');

You are trying to create an instance of a variable that has been instantiated in the constructor of your class. You are trying to do something like const myString = new "I am a string and I can not be instantiated"

When you do:

genericError: GenericException;

What you are doing is defining a class variable which is of GenericExpection type (Remember that only classes can be instantiated, not variables). If you'd like to follow your architecture you can do something like:

  async checkCar() {
    return new Promise(async (resolve: any, reject: any) => {
      //** Imagine some business logic that fails */
      this.genericError = new GenericException('Fail Reason bla bla');
      return reject(this.genericError);
    })
  }

or

  async checkCar() {
    return new Promise(async (resolve: any, reject: any) => {
      //** Imagine some business logic that fails */
      const passwordsNotMatchErr = new GenericException('Fail Reason bla bla');
      return reject(passwordsNotMatchErr);
    })
  }

Upvotes: 3

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