But the point of code is functionality (function) not expression
In truth, this term 'expressive' is a synonym for the intangible quality of JS that is also called 'flexibility'. As a voluptuous term, that can mean anything to anyone, 'Expressiveness' has potential to uniquely identify this concept.
Which is a great segway to the first part of your question:
This is the result of that flexibility and expressiveness.
There are many styles of JS, and (with windows 8, Chrome OS) there will probably be many more.
To find your style: you will have to try a few flavors; it is like ice-cream.
Understanding why JS is flexible and expressive is an exciting journey worth taking.
Hope that helps.