Channel Sidebar with Unread Badges

Context

You are building the channel sidebar for a PubNub Chat SDK-based messaging application. The sidebar shows all channels the current user belongs to, along with a badge indicating how many new messages they have not yet seen in each channel. When a user opens a channel, the badge should clear by recording that the user has seen the latest content. The sidebar also needs to load recent messages when a channel is selected.

Task

Write a JavaScript module (channel-sidebar.js) that provides:

1. A function to fetch all channels the current user is a member of, along with the number of unseen messages in each
2. A function to mark a channel as fully seen by the current user
3. A function to load the most recent messages for a selected channel, with the ability to load older messages for scrollback

Assume a Chat SDK instance is passed into each function.

Expected Outputs

• A channel-sidebar.js file with functions for building a channel sidebar with unseen message tracking and message loading.