implementing nested loops and promise resolution in asynchronous JavaScript code
I keep running into I'm sure I'm missing something obvious here, but I've been banging my head against this for hours... I'm working with a question with nested loops in my JavaScript code that involves asynchronous operations using Promises. The code is meant to iterate over a list of user IDs and fetch some data for each user, but I find that the final output is not as expected. The fetch function is asynchronous, and I believe I'm working with issues with the timing of the data retrieval. Here's a simplified version of my code: ```javascript const userIds = [1, 2, 3, 4, 5]; async function fetchData(userId) { return new Promise((resolve) => { setTimeout(() => { resolve(`Data for user ${userId}`); }, 1000); }); } async function processUsers() { const results = []; for (let userId of userIds) { let data = await fetchData(userId); results.push(data); } console.log(results); } processUsers(); ``` I'm expecting the output to be an array with fetched data for each user once all the promises are resolved. However, the output seems to be delayed until all iterations are complete, and I sometimes get unexpected or incomplete results depending on the execution timing. I initially thought using `await` in a for-loop would handle each promise sequentially, but I'm still not sure if that's the best approach. I also tried using `Promise.all()` with `map()`, but I ended up with a similar scenario. Here’s that version: ```javascript async function processUsersParallel() { const results = await Promise.all(userIds.map(userId => fetchData(userId))); console.log(results); } processUsersParallel(); ``` Using `Promise.all()` seems to fetch all data correctly, but I'm worried about the performance implications when the `userIds` array gets larger. How should I handle this to ensure I fetch data efficiently without risking overwhelming the API? Is there a more optimal pattern or best practice I should follow? I'm working on a API that needs to handle this. Any ideas what could be causing this? I'm working on a service that needs to handle this. Thanks in advance! I've been using Javascript for about a year now. I'm working with Javascript in a Docker container on Ubuntu 20.04.