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Hey everyone, I'm trying to get a solid grasp on asynchronous JavaScript, specifically promises and async/await. I understand the basic concept of non-blocking operations, but I'm struggling with error handling and chaining multiple asynchronous operations in a readable way.

Here's a simplified example I'm working with:

function fetchData(url) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      if (url === '/api/data') {
        resolve({ data: 'Sample data received!' });
      } else {
        reject(new Error('Invalid URL'));
      }
    }, 1000);
  });
}

async function processData() {
  try {
    const response = await fetchData('/api/data');
    console.log(response.data);
    
    const moreData = await fetchData('/api/more'); // This will reject
    console.log(moreData.data);
  } catch (error) {
    console.error('An error occurred:', error.message);
  }
}

processData();
                    

I get the expected output for the first `fetchData`, but the error message for the second call seems a bit generic. Are there best practices for structuring these `try...catch` blocks when dealing with many sequential async operations?

Hey @AsyncMaster! Great question. Your approach with `async/await` and `try...catch` is the right direction for error handling.

For more granular error handling, you can nest `try...catch` blocks or use multiple `await` statements, each with its own `catch` if you need to differentiate errors from specific calls. However, for sequential operations where one failure should stop the chain, your current setup is fine. The key is often in the errors you're rejecting with.

Consider this refinement:

function fetchData(url) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      if (url === '/api/data') {
        resolve({ data: 'Sample data received!' });
      } else if (url === '/api/more') {
        reject({ status: 404, message: 'Data endpoint not found.' });
      } else {
        reject(new Error('Invalid URL'));
      }
    }, 1000);
  });
}

async function processDataImproved() {
  try {
    const response1 = await fetchData('/api/data');
    console.log('First data:', response1.data);

    const response2 = await fetchData('/api/more');
    console.log('Second data:', response2.data);

    const response3 = await fetchData('/api/final');
    console.log('Third data:', response3.data);

  } catch (error) {
    if (error.status === 404) {
      console.error('Data not found:', error.message);
    } else {
      console.error('An unexpected error occurred:', error.message || error);
    }
  }
}

processDataImproved();
                    

By rejecting with an object that includes status or specific error codes, your `catch` block can become more intelligent. Also, using `Promise.all` or `Promise.allSettled` can be useful if you have independent operations you want to run concurrently and then process all results (or failures).

Thanks for the explanation @CodeGuru! I was also wondering about structuring promises. Is there a way to make long chains of `.then()` more readable when not using `async/await`?