Rails is now using "Coffeescript" rather than vanilla Javascript.

• A little book on Coffescript
• Coffeescript cookbook

Coffeescript is a syntactical sugar coating on Javascript that some people like. I think it is stupid and needless, and there are plenty of people who agree:

• Why I don't use Coffeescript

Javascript is a perfectly nice and readable language, whereas coffeescript is terse and cryptic.
I say that if it isn't broken, don't fix it -- or let me make an even stronger statement,
if it isn't broken, don't break it.

Ditching coffeescript in rails

• Remove the coffeescript gem from your Gemfile
• Just use files with ".js" extensions in app/assets/javascripts

Ways in which coffeescript sucks

You say coffeescript isn't cryptic, consider this:

We use $ ->
which is shorthand for jQuery ->
which in turn is shorthand for $(function() { blah blah }); 
which in turn is shorthand for $(document).ready(function() { blah blah }); 

The absolutely most useful thing you can know about coffeescript is that you can use backticks to embed good old javascript into coffeescript files. So, where rails is expecting you to give it coffeescript, just use backticks and give it javascript!! Hurrah!

Some basics about coffeescript

A single pound sign serves as a comment

You get to use ruby style interpolation of variables into strings.

Coffeescript adds some cute looping constructs:

    print x for x in array
    print key,val for key,val of hash

Also coffeescript adds what it calls "splats", though it documents them poorly. All they are is a means to do a C-varargs kind of thing to gather up a variable number of arguments into an array. The syntax is three dots (...) rather than *x as in ruby. The following would gather up all arguments into a single array:

    (args...)->

function addem ( n1, n2 ) { return n1 + n2; };

convert = (n1, n2) -> n1 + n2

In coffeescript the words "var" and "function" are illegal, as are semcolons. Not only that, whitespace is significant (the horror!). The vague concept about whitespace is that you can replace semicolons with tabs. Pretty much the same brain damaged mess as python. Excuse me while I go puke.