But the point of code is functionality (function) not expression
(form).
This used to be true, but we are finding it evolve in contemporary solutions. First, HTML provides the form. JavaScript is the behavior layer. To that, expressive behavior is a large part of what is requested for rich web applications. In other words, rich and responsive interactions, are behavior; and being able to express them well is a key to the capacity of programmatic implementation. So, expressiveness.
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:
It seems like there are many different styles to write JavaScript,
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.
Here is another TIP: the things that look like egyptian heiroglyphs (at first), eventually begin to turn into identifiable patterns. Picking these 'design patterns' out, gives you the ability to understand all styles of JavaScript.
Understanding why JS is flexible and expressive is an exciting journey worth taking.
Hope that helps.