Hard Rock CoffeeScript

Flow control

The convention of optional parentheses continues with CoffeeScript's if and else keywords.

CoffeeScript

if true == true
  "Rock'n'Roll"

if true != true then "Let it be"

if 1 > 0 then "Ok" else "Y2K!"

JavaScript

if (true === true) {
  "Rock'n'Roll";
}
if (true !== true) {
  "Let it be";
}
if (1 > 0) {
  "Ok";
} else {
  "Y2K!";
}

As you can see above, if the if statement is on one line, you'll need to use the then keyword, so CoffeeScript knows when the block begins. Conditional operators (?:) are not supported, instead you should use a single line if/else statement.

CoffeeScript also includes a Ruby idiom of allowing suffixed if statements.

CoffeeScript

alert "It's cold!" if heat < 5

JavaScript

if (heat < 5) {
  alert("It's cold!");
}

Instead of using the exclamation mark (!) for negation, you can also use the not keyword - which can sometimes make your code more readable as exclamation marks can be easy to miss.

CoffeeScript

if not true then "Rock'n'Roll"

JavaScript

if (!true) {
  "Rock'n'Roll";
}

In the example above, we could also use the CoffeeScript's unless statement, the opposite of if.

CoffeeScript

unless true
  "Rock'n'Roll"

JavaScript

if (!true) {
  "Rock'n'Roll";
}

In a similar fashion to not, CoffeeScript also introduces the is statement, which translates to ===.

CoffeeScript

if true is 1
  "Type coercion fail!"

JavaScript

if (true === 1) {
  "Type coercion fail!";
}

As an alternative to is not, you can use isnt.

CoffeeScript

if true isnt true
  alert "Try to rock as hard as you can!"

You may have noticed in the examples above, that CoffeeScript is converting == operators into === and != into !==. This is one of my favorite features to the language, and yet one of the most simple. What's the reasoning behind this? Well frankly JavaScript's type coercion is a bit odd, and its equality operator coerces types in order to compare them, leading to some confusing behaviors and the source of many bugs.

Chained Comparisons

CoffeeScript borrows chained comparisons from Python — making it easy to test if a value falls within a certain range.

CoffeeScript

PinkFloydAlbums = 14
fromTenToTwenty = 20 > PinkFloydAlbums > 10 # true

JavaScript

var PinkFloydAlbums, fromTenToTwenty;
PinkFloydAlbums = 14;
fromTenToTwenty = (20 > PinkFloydAlbums && PinkFloydAlbums > 10);