1. Resources recommend by Coursera course
JavaScript is a complex language that would be impossible to teach entirely in a course such as this, but there are many additional resources that you can use to learn more.
This online book is very good:
The w3schools have good tutorials:
as does Mozilla:
https://developer.mozilla.org/en-US/Learn/JavaScript
There are many, many more resources out there and a web search should quickly throw up answers to most questions
2. jQuery
In this course we will be using the library jQuery to manipulate HTML DOM. While it is possible to do this in plain JavaScript, jQuery makes it much easier.
The main jQuery site and download is here:
jQuery has very extensive documentation, which you can find here:
Having said that, the API documentation isn't the best place to start learning. The w3schools have a number of tutorials:
http://www.w3schools.com/jquery/
as well as the jQuery site itself: