Custom TypeScript Validation Errors

TypeScript Error Handling : Exercise-5 with Solution

Write a custom TypeScript error class called `ValidationException` that extends the built-in `Error` class. Use this custom error class to throw and catch validation errors with custom error messages.

Sample Solution:

TypeScript Code:

class ValidationException extends Error {
  constructor(message: string) {
    super(message);
    this.name = 'ValidationException';
  }
}

// Example usage:
function validateAge(age: number): void {
  if (age < 18) {
    throw new ValidationException('Age must be 18 or older.');
  }
}

try {
  const userAge = 12; // Change the age to test validation
  validateAge(userAge);
  console.log('Validation passed.');
} catch (error) {
  if (error instanceof ValidationException) {
    console.error(`Validation Error: ${error.message}`);
  } else {
    console.error(`Unexpected Error: ${error.message}`);
  }
}

Explanations:

In the exercise above -

• First, define a custom error class called "ValidationException" that extends the built-in "Error" class. It takes a custom error message as a parameter and sets the error name.
• Inside the "validateAge()" function, we check if the provided age is less than 18 and throw a 'ValidationException' with a custom error message if validation fails.
• In the try-catch block, we call the 'validateAge' function with a user's age. If validation fails, we catch the 'ValidationException', display the custom error message, and handle it accordingly. If another unexpected error occurs, we catch it as well and display a generic error message.

Output:

Unexpected Error: Age must be 18 or older

TypeScript Editor:

See the Pen TypeScript by w3resource (@w3resource) on CodePen.

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