typescript-async-patterns

TypeScript Async Patterns

Master asynchronous programming patterns in TypeScript, including Promises, async/await, error handling, async iterators, and advanced patterns for building robust async applications.

Promises and async/await

Basic Promise Creation

// Creating a Promise
function delay(ms: number): Promise<void> {
  return new Promise((resolve) => {
    setTimeout(resolve, ms);
  });
}

// Promise with value
function fetchUserData(userId: string): Promise<User> {
  return new Promise((resolve, reject) => {
    // Simulated API call
    setTimeout(() => {
      if (userId) {
        resolve({ id: userId, name: 'John Doe' });
      } else {
        reject(new Error('Invalid user ID'));
      }
    }, 1000);
  });
}

// Using the Promise
fetchUserData('123')
  .then((user) => {
    console.log(user.name);
  })
  .catch((error) => {
    console.error('Error:', error.message);
  });

async/await Syntax

interface User {
  id: string;
  name: string;
  email: string;
}

interface Post {
  id: string;
  userId: string;
  title: string;
  content: string;
}

// Async function declaration
async function getUserPosts(userId: string): Promise<Post[]> {
  try {
    const user = await fetchUserData(userId);
    const posts = await fetchPostsByUser(user.id);
    return posts;
  } catch (error) {
    console.error('Failed to fetch user posts:', error);
    throw error;
  }
}

// Async arrow function
const getUserProfile = async (userId: string): Promise<User> => {
  const user = await fetchUserData(userId);
  return user;
};

// Using async/await
async function main() {
  const posts = await getUserPosts('123');
  console.log(`Found ${posts.length} posts`);
}

Type-Safe Promise Wrappers

type Result<T, E = Error> =
  | { success: true; data: T }
  | { success: false; error: E };

async function safeAsync<T>(
  promise: Promise<T>
): Promise<Result<T>> {
  try {
    const data = await promise;
    return { success: true, data };
  } catch (error) {
    return {
      success: false,
      error: error instanceof Error ? error : new Error(String(error)),
    };
  }
}

// Usage
async function example() {
  const result = await safeAsync(fetchUserData('123'));

  if (result.success) {
    console.log(result.data.name);
  } else {
    console.error(result.error.message);
  }
}