class AppError extends Error {
  constructor(message, statusCode) {
    super(message);
    this.name = this.constructor.name;
    this.statusCode = statusCode;
  }
}

class ValidationError extends AppError {
  constructor(message) {
    super(message, 400);
    this.fields = [];
  }
}

function riskyOperation(value) {
  if (value === null) throw new ValidationError("Null value");
  if (value < 0) throw new AppError("Negative value", 422);
  return value * 2;
}

const results = [];

for (const val of [10, null, -5, 3]) {
  try {
    results.push(riskyOperation(val));
  } catch (e) {
    if (e instanceof ValidationError) {
      results.push(`Validation:${e.statusCode}`);
    } else if (e instanceof AppError) {
      results.push(`App:${e.statusCode}`);
    } else {
      results.push("Unknown");
    }
  }
}

console.log(results.join(" | "));