News Aggregator with Hundreds of Feed Channels

Context

You are building a personalized news aggregator where each news source publishes to its own PubNub channel. A user can follow up to 500 different news sources. When a news source publishes an article, it goes to that source's dedicated channel. The client application needs to receive articles from all followed sources in real time, and also needs to send "read receipts" back to each source's channel when the user reads an article.

Task

Write a JavaScript module (news-feed-manager.js) that:

1. Manages subscribing a user to all their followed news source channels efficiently
2. Handles adding and removing followed sources dynamically
3. Sends read receipt messages to the appropriate channel when an article is read
4. Documents any platform limits that affect the design

Assume a PubNub instance is passed in during initialization.

Expected Outputs

• A news-feed-manager.js file with a class or set of functions managing the subscription and messaging logic for the news aggregator.