W3Schools Tryit Editor

// @ts-check

// Simulated async fetch helpers to avoid network dependency in TryIt
function fakeFetchUser(userId) {
  return Promise.reject(new Error('HTTP error! status: 500'));
}

function fakeFetchPosts(userId) {
  return Promise.reject(new Error('HTTP error! status: 404'));
}

/**
 * @param {number} userId
 * @returns {Promise<{id:number,name:string,email:string}>}
 */
async function fetchUser(userId) {
  try {
    // Simulate a failing request
    // In a real app: const response = await fetch(`/api/users/${userId}`)
    return await fakeFetchUser(userId);
  } catch (error) {
    if (error instanceof Error) {
      console.log('Failed to fetch user:', error.message);
    }
    throw error;
  }
}

/**
 * @param {number} userId
 * @returns {Promise<Array<{id:number; title:string}>>}
 */
function fetchUserPosts(userId) {
  // In a real app: return fetch(`/api/users/${userId}/posts`).then(...)
  return fakeFetchPosts(userId)
    .then(() => [])
    .catch((error) => {
      if (error instanceof Error) {
        console.log('Failed to fetch posts:', error.message);
      }
      return [];
    });
}

// Run demo
fetchUser(1).catch(() => {/* swallow for demo */});
fetchUserPosts(1).then((posts) => {
  console.log('Posts length:', posts.length);
});