Throwing Custom Errors

JavaScript allows throwing custom errors using the throw statement:

Any expression can be thrown, but it’s common to throw Error objects or instances of custom error classes.

Custom error classes can extend the built-in Error class to provide specific error types with meaningful names and messages.

This enables more precise error handling, allowing different error types to be treated differently in catch blocks.

class ValidationError extends Error {
  constructor(message) {
    super(message);
    this.name = "ValidationError";
  }
}

function validateAge(age) {
  if (age < 0) {
    throw new ValidationError("Age cannot be negative");
  }
  if (age > 150) {
    throw new ValidationError("Age is too high");
  }
  return true;
}

try {
  validateAge(-5);
} catch (error) {
  if (error instanceof ValidationError) {
    console.log("Validation error: " + error.message);
  } else {
    console.log("Unknown error: " + error);
  }
}
// Output: Validation error: Age cannot be negative