Description:

When the left sidebar has many channels, we have a top/bottom unread bar to notice users scroll up or down to check the message.
There is a feature for this in client/lib/menu.js EventEmitter but currently it's not working.

Steps to reproduce:

1. Creat some channels, or reduce the height of chat window until see the scrollbar for rooms list.
2. Send a message to the channel at bottom.
3. Use another account and keep the scroll at top of rooms list.

Expected behavior:

Show the bottom-unread-rooms bar at the bottom.

Actual behavior:

Currently, it's not working

Server Setup Information:

• Version of Rocket.Chat Server: 3.0.3
• Operating System: CentOS 7
• Deployment Method: Manual Installation
• Number of Running Instances: 1
• DB Replicaset Oplog: Enabled
• NodeJS Version: v12.14.0
• MongoDB Version: 4.0.13

Client Setup Information

• Desktop App or Browser Version: Chrome 80 / Rocket Client v2.17.7
• Operating System: MacOS

Additional context

I see this feature was defined in client/lib/menu.js EventEmitter but currently it's not working.
I think because of $('li.has-alert') selector is not correct, there is not has-alert class that was used in the whole client at all, it should be .sidebar-item--unread.

And one more thing, currently when user focus on another room and get message, the event will not be triggered.
Because the menu.updateUnreadBars(); only be triggered on scroll .rooms-list.

Relevant logs:

Browser logs, the uid of undefined is another bug that I cannot find out 😅

Exception from Tracker recompute function:
560a7315be0500abf54ae7cfbadb6b22b5066ae9.js?meteor_js_resource=true:1 TypeError: Cannot read property 'uid' of undefined
    at 560a7315be0500abf54ae7cfbadb6b22b5066ae9.js?meteor_js_resource=true:971
    at t._compute (560a7315be0500abf54ae7cfbadb6b22b5066ae9.js?meteor_js_resource=true:679)
    at t._recompute (560a7315be0500abf54ae7cfbadb6b22b5066ae9.js?meteor_js_resource=true:679)
    at Object.o._runFlush (560a7315be0500abf54ae7cfbadb6b22b5066ae9.js?meteor_js_resource=true:679)
    at a (560a7315be0500abf54ae7cfbadb6b22b5066ae9.js?meteor_js_resource=true:1)