For this second part of the series, we'll dig into CoffeeScript operators and their aliases, which make our lives easier and our code much cleaner and more expressive. In case you missed the first part I recommend you have a look at it, I'm sure you'll find something interesting.
Update: Table of contents
- CoffeeScript gotchas (part 1): Comments, strings, booleans, arrays and functions
- Coffeescript gotchas (part 2): Operators and aliases
- Coffeescript gotchas (part 3): Switch statement and loops
- Coffeescript gotchas (part 4): Scope and Objects
Basic operators and their aliases
When it comes to
if statements (and not only them), CoffeeScript provides many syntax aliases that keep our code clean and readable. For starters, we can forget triple equals (===) and negative double equals (!==), and use their easier aliases, the
isnt keywords. Have a look at the example below.
name = "John" if name is "John" # true ( is equals === ) console.log('is demonstration') if name isnt "Johnny" # false ( isnt equals !== ) console.log('isnt demonstration')
You can also use the
Want to make it even more readable? You can even replace the
if not statement with the much more descriptive
unless keyword. It makes more sense in some cases:
# if not === unless person = isRunning : false, startRunning : -> console.log('start running!') if not person.isRunning person.startRunning() unless person.isRunning person.startRunning()
Finally, you can forget boolean operators such as double ampersands (
&&) and the double vertical bars (
||) and start using the much more convenient
name = 'John' sex = 'male' isCool = true if name is "John" and sex is "male" # compiles as if ( name === "John" && sex === "male" ) console.log('do something') if name is "John" or isCool is true # compiles as if ( name === "John" || isCool === true ) console.log('do something else')
maxValue = 10 minValue = 1 value = if 10 > 0 then 5 else 15 # value = 5 document.write(value)
CoffeeScript's question mark operator
This is a unique CoffeeScript feature that checks if a variable (or property) has a value. So it basically tests if the value isn't
null or of type
undefined. Keep in mind that this is not testing if a value is "falsey" (like a empty string, number 0, empty array, etc.). For more details on "truthy" and "falsy" values have a look at this excellent article on Sitepoint.
if name? # compiles as if ( name !== null || name !== "undifined" ) document.write('Safely use name value.')
You can also use this feature on object properties or when you want to check if the value isn't
null or of type
undefined. Have a look at the examples below and discover a nicely added feature that will save you a lot of typing...
person = name: 'John' console.log( person?.name ) nullName = null nullName?= "Johnny" console.log(nullName) nullName = null otherName = nullName ? "Yiannis" console.log(otherName)
The OR operator (on value assignments)
It looks better and more compact...
name = false # falsy value name ||= "John" # name || (name = "John"); console.log(name)
Another CoffeeScript only feature. If your condition is between a range you can finally combine them, just like in algebra. Nicely done.
x = 8 if 0 <= x <= 10 # compiles to if ( 0 <= x && x <= 10 ) console.log('true')
As you can see CoffeeScript can be very expressive and in many cases you can write code that is as expressive as english! The well chosen aliases make the entire experience more fun and let you focus more on problem solving than on typos and missing curly braces.
If you like this article, stay tuned because the following CoffeeScript articles will be mind blowing...