CoffeeScript Notes

This is my study book of CoffeeScript Accelerated JavaScript Development.

Embedding JS in CS

• Just put your JS code surrounding it with backticks

   console.log `impatient ? useBackticks() : learnCoffeeScript()`
  

• CS wraps code for namespacing, but you can remove it with -b (‘bare’) flag

• we can execute a function using do

   do fn
   fn()
  

• A function will be always defined with var, in CS we have no way to define functions with function keyword, the one exception is when we use the class keyword
• Strict equality or Nothing, CS dont provide anyway to use the equality comparator of JS (==), is and == will always do strict equality

Again; - Every function creates a scope, and the only way to create a scope is to define a function - A variable lives in the outermost scope in which an assignment has been made to that variable - Outside of its scope, a variable is invisible

Variable’s scope is defined explicitly in JS using the var keyword while CS infers scope from assignments.

• Shadowing variable name is a bad thing, dont do this

   x = 5
   triple = (x) -> x *= 3
   triple x                // => 15
   x                       // => 5
  
   hey = (x = x) -> console.log x
   hey()                   // => undefined
   x                       // => 5
  

• context = this
• scope = where the variable’s are resolved

• The context is determined purely by how a function is called; unlike scope, it has nothing to do with where the function is defined.

• When the new keyword is put in front of a function call, its context is the new object.
• When a function is called with call or apply, the context is the first argument given.

• Otherwise, if a function is called as an object property (obj.func) or ob[“func”], it runs in that object’s context.

• How => works

   callback = (message) => @voicemail.push message
  
   var callback;
   callback = (function(__this) {
       var __func = function (message) {
           return this.voicemail.push(message);
       };
       return function () {
           return __func.apply(__this, arguments);
       };
   })(this);
  

• You can use arbitrary expressions as default arguments, the expression will be execute from whatever context the function is being called in.

---

spoiler = (filter..., theEnding) -> console.log theEnding
spoiler 'Darth Vader is Luke\'s father!'              // => 'Darth Vader is Luke's father!'

birds = [ 'duck', 'duck', 'duck', 'coffee!' ]
[ ducks..., coffee ] = birds
ducks                                                 // => 'duck, duck, duck'
coffee                                                // => 'coffee'

Collections and Iteration

• In JS every object is a hash, and almost everything is an Object. Except primitive values (booleans, numbers and strings) and special constants like undefined and NaN

• When the CS compiler sees :, it know that you’re building an object.

   drawSprite x, y, invert:true
  
   drawSprite(x, y, {
       invert: true
   });
  

• Same-Name Key-Value Pairs { me }, works only with explicit curly braces

• Soaks ‘a?.b’

   cats?['Garfield']?.eat() if lasagna?
  
   abc = [ 'a', 'b', 'c', 'd' ]
   abc[0..-1]                      # => [ 'a', 'b', 'c' ]
   abc[2..0]                       # => [ ]: always will be empty if the first number is greater than secound
  

.. defines an inclusive range … defines a exclusive range

    [1..5]                          # => [1, 2, 3, 4, 5]
    [1...5]                         # => [1, 2, 3, 4]

• we can use splice with ranges to

   arr = ['a', 'c']
   ar[1...2] = [ 'b' ]             # => ['a', 'b']
  

• Curiously, JS provides strings with a slice method, even though its behavior is identical to substring. This is handy, because it means you can use CoffeeScript’s slicing syntax to get substrings.

   'The year is 2013'[-4..]        # => 2013
  

• hasOwnProperty, for own

   for own sword of Kahless
  
  
   for sword of Kahless
       continue unless Kahless.hasOwnProperty(sword)
  

• with for.. of we can use when

• with for.. in and array like we can use by

• When you write for x of obj or for x in arr, you’re making assignments to a variable named x in the current scope. You can take advantage of this by using those variables after the loop.

• We can use do to capture the loop variable on each iteration

   for name, occupation of murderMysteryCharacters
       break if occupation is 'butler'
  
   console.log "#{name} did it!"
  
   for x in arr
       do (x) ->
           setTimeout (-> console.log x), 0
  

• while, until and loop
• loop is forever until break

Pattern Matching (or, Destructuring Assignment)

• It’s NOT an array or an object, its a Pattern

  [firstName, middleInitial, lastName] = ['Joe', 'T', 'Plumber']
  # firstName = 'Joe'; middleInitial = 'T'; lastName = 'Plumber'
  
  myRect =
      x: 100
      y: 200
  {x: myX, y: myY} = myRect
  
  {languages: [favoriteLanguage, otherLanguages...]} = resume
  # Take resume.languages, assign its first entry to a vari- able called favoriteLanguage, then assign the remaining entries to a new array called otherLanguages.
  

• Better to use many small files, each with a WELL-DEFINED PURPOSE! than a few large files that make readers feel like rats in a maze.

• always use the root object to set a global property

   class Tribble
       constructor: () ->
           @isAlive = true
           Tribble.count++
          
       breed: () ->
           return new Tribble if (@isAlive)
          
       die: () ->
           Tribble.count-- if (@isAlive)
           @isAlive = false
  
       @count: 0
       @makeTrouble: () ->
           console.log ('Trouble!' for i in [1..@count]).join(' ')
  

• the object itself
• the prototype object

• and the instance

• ’ strict string
• You can use “”” to write multilines strings in a human-readable format.

Docco

### Eco ### Zappa ### Zombie.js

---

• ← Previous Post
• Next Post →