JavaScript Cheat Sheet

Performance Optimizations

Tips

• develop against a set of fixtures so you're dealing with the same graphics every time you refresh the page (uploaded images, etc.). but also be able to create new things
• be able to reset the db back to the base "fixtured" state.
• use console.log and related on the client so you can see the line number (i.e. don't wrap it)
• http://jsperf.com/dynamic-arguments

Classes

class User
  has_many :posts
end

class User
  @has_many "posts"

Modules

module Associations
  included do
    
  end
  
  module ClassMethods
    def has_many(*args)
      
    end
    
    def reflections
      
    end
  end
  
  module InstanceMethods
    def reflections
      self.class.reflections
    end
  end
end

Associations = 
  included: ->

  ClassMethods:
    has_many: ->
    
    reflections: ->

  InstanceMethods:
    reflections: ->
      @constructor.reflections()

instance_eval

user.instance_eval do
  puts self.class.name
end

Object.prototype.instance_eval = (block) ->
  block.call(@)
  
user.instance_eval ->
  console.log @constructor.name

Extract Args and Options

# args is a plain array
def find(*args)
  options = args.extract_options!
end

# args is an "Arguments" object
find: ->
  args    = extract_args(arguments)
  options = extract_options(args)

Async Loops

repeater = (i) ->
  if i < length
    asyncwork ->
      repeater i + 1
repeater 0

Function Call vs. Class Performance

# http://jsperf.com/function-vs-new-object-call
class TestClass
  constructor: ->
    1 + 1

testFunction = ->
  1 + 1
  
new TestClass() # 7,486,425 ops/sec
testFunction()  # 108,392,512 ops/sec

Method vs. Getter Performance

# http://jsperf.com/function-call-vs-getter
class TestClass
  method: ->
    1 + 1
    
  getOrSet: ->
    if arguments.length > 0 then 1 + 1 else @["_getOrSet"] = arguments

Object.defineProperty TestClass.prototype, "getter", 
  get: -> 1 + 1

object = new TestClass

object.method()             # 28,804,533 ops/sec
object.getter               # 15,671,784 ops/sec (50% slower)
object.method.call(object)  # 27,044,957 ops/sec
object.method.apply(object) # 28,804,533 ops/sec
object.getOrSet()           # 2,920,880  ops/sec (90% slower)

Method Missing in JavaScript

Replace all function calls to object.send(name, arguments...) with node burrito, like this guy does: http://www.ruby-forum.com/topic/128539.

Bitwise operators

• http://stackoverflow.com/questions/1523061/performance-of-bitwise-operators-in-javascript

POSITION_BELOW: 1 << 0,
POSITION_RIGHT: 1 << 1,
POSITION_LEFT: 1 << 2,
POSITION_ABOVE: 1 << 3,
POSITION_MIDDLE: 1 << 4,