The javascript section does push forward in a different way than the HTML/CSS section. There is a lot of meat to javascript, and a limited number of lessons to get through it.
Javascript is also, from the student perspective, a paradigm shift – with HTML/CSS, many if not most of the answers were given to you, in the lessons at least. In the challenges, there were some hurdles, but nothing truly difficult.
With javascript, there is a lot more independent study. And this isn’t merely a factor of FCC, it really doesn’t matter where you turn to learn it. This is the beginning of true “programming”. Crafting HTML and CSS is more “design”, while javascript becomes far more programming.
So, when you see functions referred to that you don’t know, don’t default to the hints or answers. You have other tools at your disposal. A “true developer” will pop on over to the Mozilla Developer’s Network (MDN), and research each of these higher-order functions there. There is a WEALTH of information, and code samples, to be found on that site.
Also, research with other tools: http://devdocs.io/ is HUGE. Great reference for HTML, CSS, javascript, many libraries and frameworks, and a host of other languages (PHP, perl, Ruby, etc etc). Simply go on there, and search for map
(or, if you want to get there quicker, Array functions
).
The sign of a solid developer isn’t what she KNOWS. It’s does she know how to RESEARCH.