Handling Nested Callbacks in JavaScript Functions with Promises
I'm updating my dependencies and I'm stuck on something that should probably be simple. I'm facing a challenge with handling nested callbacks in my JavaScript function that's supposed to work with Promises. The function retrieves data from an API and then processes that data before saving it to a database. However, I'm running into a situation where the data processing seems to complete before the API call finishes, resulting in an unexpected `undefined` value when I try to access the processed data. Here’s the relevant part of the code: ```javascript function fetchDataAndProcess(url) { return fetch(url) .then(response => response.json()) .then(data => { return processData(data); }); } function processData(data) { // Simulating an async operation let processedData; setTimeout(() => { processedData = data.map(item => item.value * 2); }, 1000); return processedData; } fetchDataAndProcess('https://api.example.com/data') .then(result => { console.log('Processed result:', result); }) .catch(error => { console.error('Error:', error); }); ``` When I run this, I see `Processed result: undefined` in the console. I suspect that the `processData` function isn't returning the processed data because the asynchronous `setTimeout` is not completed before the function returns. I tried wrapping `processedData` in a Promise but it still returns `undefined`. How can I properly handle this nested callback situation to ensure that the processed data is available when I need it? Is there a better design pattern for this type of operation in JavaScript? My development environment is Windows. Has anyone else encountered this? I'm coming from a different tech stack and learning Javascript. I'd be grateful for any help.