Javascript Closure Explained - In under 3 minutes!

Can someone tell what extension he uses, that shows values instantly on the right in the comments?

The code isn't working for me.

Can you explain complex examples for closures?

What extension are you using to give you the variable value and total?

This example is unforgettable.Closure simplified indeed.

Watched it twice, feels like I've grasped it with your help.
Thanx a lot and have a good day!