Pace.js - Automatic page load progress bar
One of the Nielsen heuristics stands for
"Visibility of system status: The system should always keep users informed about what is going on, through appropriate feedback within reasonable time."

In modern web pages we've got a lot of asynchronous AJAX calls. To keep user informed what is really happening, we can simply show loading image while some calls are pending. Few days ago I was developing new website with a lot of javascript/AJAX code. I started wondering if somebody release some js library (as you know day without new js lib is the lost day) and I found Pace.js. Small, smooth and easy to use describe this great library. Just download .js file, add few line to you css and Voilà - it works!

Pacejs github