COFFEESCRIPT CoffeeScript
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File Information
CoffeeScript
Code
.coffee
text/x-coffeescript
CoffeeScript (.coffee)
Overview
CoffeeScript is a programming language that compiles into JavaScript, created by Jeremy Ashkenas in 2009. It aims to expose the good parts of JavaScript in a simple, clean syntax inspired by Python, Ruby, and Haskell. CoffeeScript enhances JavaScript with syntactic sugar, making code more readable and concise while maintaining full compatibility with existing JavaScript libraries and frameworks.
Technical Details
- File Extension:
.coffee
- MIME Type:
text/x-coffeescript
- Category: Programming Language
- First Appeared: 2009
- Paradigm: Multi-paradigm (functional, object-oriented)
- Platform: Transpiles to JavaScript (runs anywhere JavaScript runs)
Key Features
Clean Syntax
- Significant whitespace (Python-inspired)
- Minimal punctuation and brackets
- Implicit returns and variable declarations
- Simplified function syntax
JavaScript Enhancement
- Compiles to readable, idiomatic JavaScript
- No runtime dependencies
- Full access to JavaScript ecosystem
- Lexical scoping and proper variable binding
Functional Programming
- Built-in list comprehensions
- Destructuring assignment
- Function binding and arrow functions
- Classes with inheritance
Syntax Examples
Basic CoffeeScript Constructs
# Variables (no var, let, const needed)
name = "CoffeeScript"
version = 2.7
isAwesome = true
# String interpolation
greeting = "Hello, #{name}!"
message = "Version #{version} is here"
# Functions
greet = (name) ->
"Hello, #{name}!"
# Short function syntax
square = (x) -> x * x
add = (a, b) -> a + b
# Function calls (parentheses optional)
console.log greet "World"
console.log add 5, 3
console.log square 4
# Multi-line functions
calculateArea = (length, width) ->
area = length * width
console.log "Area calculated: #{area}"
area # implicit return
Control Structures
# If statements
classifyAge = (age) ->
if age < 13
"child"
else if age < 20
"teenager"
else if age < 60
"adult"
else
"senior"
# Unless (negative if)
unless user.isLoggedIn
redirectToLogin()
# One-line conditionals
message = if weather is "sunny" then "Great day!" else "Stay inside"
# Switch statements
getDayName = (dayNum) ->
switch dayNum
when 1 then "Monday"
when 2 then "Tuesday"
when 3 then "Wednesday"
when 4 then "Thursday"
when 5 then "Friday"
when 6, 7 then "Weekend"
else "Invalid day"
# While and until loops
count = 0
while count < 5
console.log "Count: #{count}"
count++
# Until loop (negative while)
until done
processNextItem()
Arrays and Objects
# Arrays
numbers = [1, 2, 3, 4, 5]
names = ["Alice", "Bob", "Charlie"]
# Array operations
numbers.push 6
first = numbers[0]
last = numbers[numbers.length - 1]
# List comprehensions
squares = (x * x for x in numbers)
evens = (x for x in numbers when x % 2 is 0)
doubled = (x * 2 for x in numbers when x > 3)
# Objects
person =
name: "John Doe"
age: 30
city: "New York"
greet: -> "Hello, I'm #{@name}"
# Alternative object syntax
config = {
host: "localhost"
port: 8080
ssl: false
}
# Accessing object properties
console.log person.name
console.log person["age"]
console.log person.greet()
Classes and Inheritance
# Class definition
class Animal
constructor: (@name, @species) ->
@alive = true
speak: ->
console.log "#{@name} makes a sound"
sleep: ->
console.log "#{@name} is sleeping"
# Inheritance
class Dog extends Animal
constructor: (name, breed) ->
super name, "Canine"
@breed = breed
speak: ->
console.log "#{@name} barks!"
wagTail: ->
console.log "#{@name} is wagging tail"
class Cat extends Animal
constructor: (name, color) ->
super name, "Feline"
@color = color
speak: ->
console.log "#{@name} meows!"
purr: ->
console.log "#{@name} is purring"
# Using classes
dog = new Dog "Buddy", "Golden Retriever"
cat = new Cat "Whiskers", "Orange"
dog.speak() # "Buddy barks!"
cat.speak() # "Whiskers meows!"
dog.wagTail() # "Buddy is wagging tail"
cat.purr() # "Whiskers is purring"
Destructuring and Pattern Matching
# Array destructuring
[first, second, ...rest] = [1, 2, 3, 4, 5]
console.log first # 1
console.log second # 2
console.log rest # [3, 4, 5]
# Object destructuring
{name, age, city} = person
console.log "#{name} is #{age} years old and lives in #{city}"
# Function parameter destructuring
processUser = ({name, email, preferences: {theme, language}}) ->
console.log "User: #{name}"
console.log "Email: #{email}"
console.log "Theme: #{theme}, Language: #{language}"
user =
name: "Alice"
email: "[email protected]"
preferences:
theme: "dark"
language: "en"
processUser user
# Default parameters
greetUser = (name = "Guest", greeting = "Hello") ->
"#{greeting}, #{name}!"
console.log greetUser() # "Hello, Guest!"
console.log greetUser "Alice" # "Hello, Alice!"
console.log greetUser "Bob", "Hi" # "Hi, Bob!"
Functional Programming Features
# Higher-order functions
applyTwice = (fn, value) ->
fn fn value
double = (x) -> x * 2
result = applyTwice double, 5 # ((5 * 2) * 2) = 20
# Function binding
@name = "Global"
obj =
name: "Object"
greet: ->
console.log "Hello from #{@name}"
delayedGreet: ->
# Arrow function preserves 'this' context
setTimeout (=> @greet()), 1000
obj.delayedGreet() # Will log "Hello from Object" after 1 second
# Partial application and currying
multiply = (a) -> (b) -> a * b
double = multiply 2
triple = multiply 3
console.log double 5 # 10
console.log triple 4 # 12
# Function composition
compose = (f, g) -> (x) -> f g x
addOne = (x) -> x + 1
double = (x) -> x * 2
addOneThenDouble = compose double, addOne
console.log addOneThenDouble 5 # 12 (5 + 1 = 6, 6 * 2 = 12)
Operators and Comparisons
CoffeeScript Operators
# Existence operator
if user.name?
console.log "User has a name: #{user.name}"
# Safe property access
console.log user.profile?.avatar?.url
# Default assignment
name ?= "Anonymous"
config.timeout ?= 5000
# Comparison operators
if age is 25 # === in JavaScript
if name isnt "John" # !== in JavaScript
# In operator
if "admin" in user.roles
console.log "User is an admin"
# Of operator (for objects)
if "name" of user
console.log "User object has name property"
# Range operator
numbers = [1..10] # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
letters = ['a'..'e'] # ['a', 'b', 'c', 'd', 'e']
countdown = [10..1] # [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
# Splat operator (spread)
first = (head, tail...) ->
console.log "First: #{head}"
console.log "Rest: #{tail}"
first 1, 2, 3, 4 # First: 1, Rest: [2, 3, 4]
Asynchronous Programming
Callbacks and Promises
# Callback-style
loadData = (callback) ->
setTimeout ->
data = {message: "Data loaded"}
callback null, data
, 1000
loadData (err, data) ->
if err
console.error "Error:", err
else
console.log "Data:", data
# Promise-style
loadDataPromise = ->
new Promise (resolve, reject) ->
setTimeout ->
if Math.random() > 0.1
resolve {message: "Data loaded successfully"}
else
reject new Error "Failed to load data"
, 1000
# Using promises
loadDataPromise()
.then (data) ->
console.log "Success:", data
.catch (error) ->
console.error "Error:", error
# Async/await style (modern CoffeeScript)
fetchUserData = (userId) ->
try
response = await fetch "/api/users/#{userId}"
data = await response.json()
return data
catch error
console.error "Failed to fetch user:", error
throw error
# Generator functions
fibonacci = ->
[a, b] = [0, 1]
loop
yield a
[a, b] = [b, a + b]
fib = fibonacci()
console.log fib.next().value # 0
console.log fib.next().value # 1
console.log fib.next().value # 1
DOM Manipulation and jQuery Integration
DOM Operations
# Event handling
$ -> # Document ready
$('#button').click ->
alert 'Button clicked!'
$('.item').hover(
-> $(this).addClass 'highlight'
-> $(this).removeClass 'highlight'
)
# Form handling
$('#contact-form').submit (e) ->
e.preventDefault()
name = $('#name').val()
email = $('#email').val()
message = $('#message').val()
if validateForm name, email, message
submitForm {name, email, message}
else
showError "Please fill in all fields"
validateForm = (name, email, message) ->
name.length > 0 and email.includes('@') and message.length > 0
submitForm = (data) ->
$.ajax
url: '/contact'
method: 'POST'
data: data
success: (response) ->
showSuccess "Message sent successfully!"
$('#contact-form')[0].reset()
error: (xhr, status, error) ->
showError "Failed to send message: #{error}"
# Dynamic content
createUserCard = (user) ->
card = $ """
<div class="user-card">
<h3>#{user.name}</h3>
<p>#{user.email}</p>
<button class="delete-btn" data-id="#{user.id}">Delete</button>
</div>
"""
card.find('.delete-btn').click ->
if confirm "Delete user #{user.name}?"
deleteUser user.id
card
# Append to container
$('#users-container').append createUserCard user for user in users
Testing with CoffeeScript
Unit Testing
# Using Mocha and Chai
{expect} = require 'chai'
describe 'Calculator', ->
calculator = null
beforeEach ->
calculator = new Calculator()
describe '#add', ->
it 'should add two numbers correctly', ->
result = calculator.add 2, 3
expect(result).to.equal 5
it 'should handle negative numbers', ->
result = calculator.add -5, 3
expect(result).to.equal -2
describe '#divide', ->
it 'should divide two numbers correctly', ->
result = calculator.divide 10, 2
expect(result).to.equal 5
it 'should throw error for division by zero', ->
expect(-> calculator.divide 10, 0).to.throw 'Division by zero'
# Class being tested
class Calculator
add: (a, b) -> a + b
subtract: (a, b) -> a - b
multiply: (a, b) -> a * b
divide: (a, b) ->
if b is 0
throw new Error 'Division by zero'
a / b
Build Tools and Compilation
Compilation Setup
# Install CoffeeScript globally
npm install -g coffeescript
# Compile single file
coffee -c script.coffee
# Watch and compile automatically
coffee -w -c script.coffee
# Compile directory
coffee -c src/
# Output to specific directory
coffee -o lib/ -c src/
Gulp Build Configuration
# gulpfile.coffee
gulp = require 'gulp'
coffee = require 'gulp-coffee'
concat = require 'gulp-concat'
uglify = require 'gulp-uglify'
sourcemaps = require 'gulp-sourcemaps'
gulp.task 'coffee', ->
gulp.src 'src/**/*.coffee'
.pipe sourcemaps.init()
.pipe coffee bare: true
.pipe concat 'app.js'
.pipe uglify()
.pipe sourcemaps.write '.'
.pipe gulp.dest 'dist/'
gulp.task 'watch', ->
gulp.watch 'src/**/*.coffee', ['coffee']
gulp.task 'default', ['coffee', 'watch']
Webpack Configuration
// webpack.config.js for CoffeeScript
module.exports = {
entry: './src/app.coffee',
output: {
filename: 'bundle.js',
path: __dirname + '/dist'
},
module: {
rules: [
{
test: /\.coffee$/,
use: 'coffee-loader'
}
]
},
resolve: {
extensions: ['.coffee', '.js']
}
};
Development Tools
Editors and IDEs
- VSCode with CoffeeScript extensions
- Sublime Text with CoffeeScript package
- Atom with built-in CoffeeScript support
- WebStorm with CoffeeScript plugin
Debugging
# Source maps for debugging
console.log "Debug point reached"
debugger # Breakpoint in browser dev tools
# Logging helper
log = (message, data) ->
console.log "[#{new Date().toISOString()}] #{message}", data
log "User logged in", {userId: 123, name: "Alice"}
# Assert function
assert = (condition, message) ->
unless condition
throw new Error "Assertion failed: #{message}"
assert user.isValid(), "User must be valid"
Migration and Modern Alternatives
TypeScript Migration
// Modern TypeScript equivalent
interface User {
name: string;
age: number;
city: string;
}
class UserService {
private users: User[] = [];
addUser(user: User): void {
this.users.push(user);
}
findUser(name: string): User | undefined {
return this.users.find(user => user.name === name);
}
}
Modern JavaScript Features
// ES6+ equivalent of CoffeeScript features
const greet = (name = "Guest") => `Hello, ${name}!`;
const users = [
{ name: "Alice", age: 25 },
{ name: "Bob", age: 30 }
];
const adults = users
.filter(user => user.age >= 18)
.map(user => ({ ...user, isAdult: true }));
class Animal {
constructor(name, species) {
this.name = name;
this.species = species;
}
speak() {
console.log(`${this.name} makes a sound`);
}
}
Common Use Cases
Web Development
- Frontend application development
- jQuery plugin creation
- Single-page applications
- Progressive web apps
Node.js Applications
- Server-side scripting
- API development
- Build tools and automation
- Command-line utilities
Game Development
- Browser-based games
- HTML5 canvas applications
- Phaser.js games
- Interactive animations
Data Visualization
- D3.js applications
- Chart and graph generation
- Interactive dashboards
- Scientific visualizations
Notable Applications
- Dropbox: Early web interface
- GitHub: Parts of the web interface
- Basecamp: Web application components
- Various startups: Rapid prototyping
- Open source projects: Build tools and utilities
Learning Resources
- "The Little Book on CoffeeScript" by Alex MacCaw
- "CoffeeScript: Accelerated JavaScript Development" by Trevor Burnham
- Official CoffeeScript documentation
- "Smooth CoffeeScript" interactive book
- CoffeeScript community tutorials and examples
While CoffeeScript usage has declined with the advent of ES6+ and TypeScript, it remains an interesting language that influenced modern JavaScript development and demonstrated how transpilation could improve developer experience.
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