👀 Views: 60 💬 Answers: 1 📅 Created: 2025-09-06

javascript react arrays JavaScript

I've searched everywhere and can't find a clear answer. Currently developing a dashboard application using React and Redux, and I've run into a challenge while trying to merge two arrays of objects. Each object in the first array represents a user, while the second array contains user activity logs. I want to enrich the user data with their latest activity based on a common `userId` property. Here’s what I’ve tried so far: ```javascript const users = [ { userId: 1, name: 'Alice' }, { userId: 2, name: 'Bob' }, { userId: 3, name: 'Charlie' } ]; const activities = [ { userId: 1, lastActivity: '2023-10-01' }, { userId: 2, lastActivity: '2023-10-02' }, { userId: 2, lastActivity: '2023-10-03' }, { userId: 3, lastActivity: '2023-10-01' } ]; const mergedData = users.map(user => { const userActivity = activities.filter(activity => activity.userId === user.userId); return { ...user, lastActivity: userActivity[userActivity.length - 1]?.lastActivity || 'No activity' }; }); ``` The intention was to merge the user data with their most recent activity. However, I end up getting 'No activity' for users who had activities, which suggests I’m not accessing the filtered array properly. The filter returns an array, but the `lastActivity` seems to be returning undefined in some cases. When I console log `userActivity`, it shows the expected activities, but the last one doesn't seem to be picked up correctly for users with multiple activities. Is there a more efficient way to achieve this? Or did I misunderstand how to access the last element of the filtered array? Any suggestions on optimizing this approach or best practices for merging arrays in JavaScript would be greatly appreciated! My development environment is Ubuntu. I'd really appreciate any guidance on this. Any help would be greatly appreciated! I appreciate any insights! I recently upgraded to Javascript 3.9. Any advice would be much appreciated.