This guide covers the knowledge you should have before starting the course.
(Incompleted, requires contributions)
As I mentioned earlier, I recommend you to have the basic understanding of modern programming. If you do not, you might find it difficult for you to follow the rest of the course.
You can find any online resouces that you like to learn the above knowledge, I personally recommend section 1 and section 2 of the part of javascript.info.
However, if your time is tight and you want to get your feet wet as soon as possible, the following is a quick guide on it.
Variable Declaration
Arithmetics
Logical Operators
Conditional Blocks
Loops and Iteration