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Catalog / CoffeeScript Cheatsheet

CoffeeScript Cheatsheet

A concise reference for CoffeeScript, covering syntax, features, and best practices for this elegant JavaScript dialect.

Core Syntax

Basic Structure

Function Definition

 
square = (x) -> x * x

Equivalent to:

var square = function(x) {
  return x * x;
};

Implicit Return

CoffeeScript functions implicitly return the value of the last expression.

calculate = (a, b) ->
  sum = a + b
  sum * 2  # Implicitly returned

Object Literals

 
person = {
  name: 'Alice'
  age: 30
}

Equivalent to:

var person = {
  name: 'Alice',
  age: 30
};

Array Literals

 
numbers = [1, 2, 3, 4, 5]

Equivalent to:

var numbers = [1, 2, 3, 4, 5];

String Interpolation

 
name = 'Bob'
greeting = "Hello, #{name}!"

Results in:

var name = 'Bob';
var greeting = "Hello, " + name + "!";

Multiline Strings

 
longString = """
  This is a very
  long string.
"""

Equivalent to:

var longString = "This is a very\nlong string.";

Operators and Keywords

is, isnt

Equality checks. is is === and isnt is !==.

if age is 18
  console.log 'You are 18'

not

Logical NOT. not true is equivalent to !true.

if not authenticated
  console.log 'Access denied'

and, or

Logical AND and OR.

if sunny and temp > 25
  console.log 'Enjoy the weather'

unless

The opposite of if. Executes the block if the condition is false.

unless raining
  console.log 'Lets go outside'

@

Shorthand for this. Useful in class methods.

class Person
  constructor: (@name)
  greet: -> console.log "Hello, @name!"

?

Existential operator. Returns true if a variable is not null or undefined.

console.log name?  # Checks if name exists

Control Flow & Loops

Conditional Statements

if / else

 
if age >= 18
  console.log 'Adult'
else
  console.log 'Minor'

unless

 
unless hungry
  console.log 'Not hungry'

else if

 
if score > 90
  grade = 'A'
else if score > 80
  grade = 'B'
else
  grade = 'C'

Loops

for...in

Iterates over the keys of an object.

obj = {a: 1, b: 2, c: 3}
for key, value of obj
  console.log "#{key}: #{value}"

for...of

Iterates over the elements of an array.

numbers = [10, 20, 30]
for num in numbers
  console.log num

for...from...to

Creates a range-based loop.

for i in [1..5]
  console.log i

while

 
i = 0
while i < 5
  console.log i
  i++

until

The opposite of while.

i = 0
until i >= 5
  console.log i
  i++

List Comprehensions

CoffeeScript’s list comprehensions provide a concise way to generate arrays.

squares = (x * x for x in [1..5])
# squares is now [1, 4, 9, 16, 25]

With conditions:

evenSquares = (x * x for x in [1..10] when x % 2 is 0)
# evenSquares is now [4, 16, 36, 64, 100]

Classes & Objects

Class Definition

Basic Class

 
class Animal
  constructor: (@name)
  move: ->
    console.log "#{@name} moved"

animal = new Animal('Lion')
animal.move()

Inheritance

 
class Dog extends Animal
  bark: ->
    console.log 'Woof!'

dog = new Dog('Buddy')
dog.move()
dog.bark()

Class Variables

 
class MathUtils
  @PI: 3.14159
  @square: (x) -> x * x

console.log MathUtils.PI
console.log MathUtils.square(5)

Object Creation

Creating instances of classes is straightforward:

class Point
  constructor: (@x, @y)

point = new Point(10, 20)
console.log point.x, point.y

Prototypes

CoffeeScript classes automatically manage prototypes, making inheritance and method sharing simple.

class Vehicle
  start: -> console.log 'Engine started'

class Car extends Vehicle
  drive: -> console.log 'Driving'

car = new Car()
car.start()
car.drive()

Functions

Function Definition

Basic Function

 
add = (a, b) -> a + b
console.log add(5, 3)

Functions with no arguments

 
sayHello = -> console.log 'Hello!'
sayHello()

Multiline Functions

 
calculate = (x, y) ->
  sum = x + y
  sum * 2

console.log calculate(2, 3)

Arguments

Default Arguments

 
greet = (name = 'Guest') -> console.log "Hello, #{name}!"

greet()
# Output: Hello, Guest!
greet('Alice')
# Output: Hello, Alice!

Splats (Variable Arguments)

 
sum = (numbers...) ->
  total = 0
  total += num for num in numbers
  total

console.log sum(1, 2, 3, 4)

Bound Functions

Use => instead of -> to bind the function to the current this context. This is particularly useful in event handlers and callbacks.

class Button
  constructor: (@element)
    @element.addEventListener 'click', (event) => @handleClick(event)

  handleClick: (event) ->
    console.log 'Button clicked', @element
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