Result Pattern

The Result pattern is a clean, type-safe way to handle success or failure in operations without throwing exceptions.

✅ Prevents uncontrolled exceptions from leaking into your application.
✅ Makes function return types clear and predictable.

---

What is the Result Pattern?

Instead of returning raw values or throwing errors, you wrap the outcome in a Result object.

This object has:

• A success/failure status.
• Either the successful result or the failure reason.

Example:

const result = await service.doSomething();

if (result.isSuccess()) {
  const value = result.value;
} else {
  const error = result.error;
}

✅ This forces the caller to explicitly handle both success and error cases.

---

Result API

DomusJS provides the following:

Interface

export class Result<T, E> {
  isSuccess(): boolean;
  isFailure(): boolean;
  value: T;
  error: E;
}

Static Constructors

Result.ok(value);
Result.fail(error);

Example

const result = Result.ok('User created');

if (result.isSuccess()) {
  console.log(result.value); // 'User created'
}

---

Example Use Case: Register User

Service Method

import { Result } from '@domusjs/core';

export async function registerUser(email, password): Promise<Result<User, string>> {
  if (await userExists(email)) {
    return Result.fail('Email already taken');
  }

  const user = await createUser(email, password);
  return Result.ok(user);
}

Caller Handling

const result = await registerUser('test@example.com', 'password123');

if (result.isSuccess()) {
  console.log('User registered:', result.value);
} else {
  console.error('Failed to register user:', result.error);
}

✅ This makes sure no uncaught exceptions happen.

---

Best Practices

✅ Use Result to wrap operations where failure is a normal, expected possibility.
✅ Avoid using it for critical, unexpected failures (those should be proper exceptions).
✅ Always handle both paths (ok and fail) at the call site.

---

Benefits

• Clearer code: success and error cases are always visible.
• Safer APIs: avoids forgotten .catch() blocks or missed error branches.
• Easier testing: you can easily test both successful and failing scenarios.