Best Practices for Error Handling in Typescript

After delving into articles about error handling, a thought lingers in my mind - is throwing an exception on validation logic in the value object really the most efficient approach? Take for example this class that represents a value object:

export class UserName {
  private readonly value: string;

  constructor(value: string) {
    this.value = this.validateName(value);
  }

  private validateName(value: string): string {
    value = value.trim();
    if (value === "") {
      throw new UserNameError("username is required!");
    }
    return value;
  }

  static userNameOf(name: string): UserName {
    return new UserName(name);
  }

  public isValidName(): boolean {
    if (!/^[a-zA-Z]+$/.test(this.value)) {
      throw new UserNameError("user name should contain only letters");
    }
    return true;
  }

}

I find myself pondering if there is a better way to handle errors instead of simply throwing them. Any suggestions or insights would be greatly appreciated. Thank you!

Answer №1

Value objects offer the advantage of enforcing their own invariants, promoting adherence to the "always valid" principle for entities, aggregate roots, and value objects to ensure they are never in a state that violates their invariants.

Throwing exceptions from a value object is acceptable, and it is recommended to maintain strict validation protocols. For instance, consider implementing a Username Value Object with a more rigorous isValidName() test to prevent errors during construction.

A potential refactoring approach:

export class UserName {
  private readonly value: string;

  constructor(value: string) {
    trimmed: string;
    trimmed = value.trim();
    
    if (trimmed === "") {
       throw new UserNameError("Username is required!.");
    }

    if (!/^[a-zA-Z]+$/.test(trimmed)) {
      throw new UserNameError("user name should contain only letter");
    }    

    this.value = trimmed;
  }

  static userNameOf(name: string): UserName {
    return new UserName(name);
  }
}

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