property-accessors

Property Accessors Mixin

A mixin for defining dynamic properties.

Basic Usage

To define a basic property accessor, use the accessor declaration. If you've included the mixin into a class, you define a prototype property by calling @::accessor on its prototype.

PropertyAccessors = require 'property-accessors'
 
class Vehicle
  PropertyAccessors.includeInto(this)
 
  @::accessor 'type',
    get: ->
      switch @doorCount
        when 4 then 'sedan' # i know this isn't strictly accurate 
        when 2 then 'coupe'
    set: (type) ->
      switch type
        when 'sedan' then @doorCount = 4
        when 'coupe' then @doorCount = 2
 
car = new Vehicle
car.doorCount = 2
car.type # => 'coupe' 

You can define a class-level property by extending with the mixin rather than including it (which extends the prototype).

class Vehicle
  PropertyAccessors.extend(this)
 
  @accessor 'vehicleCount', get: -> @allVehicles.length  

You can just pass a single function if you only want to define a getter:

class Vehicle
  PropertyAccessors.includeInto(this)
 
  @::accessor 'type', -> # ... 

Fancy Usage

Lazy Accessors

Lazy accessors call a function the first time a property is accessed. You are still free to overwrite this value by assigning the property explicitly.

class ScienceLab
  PropertyAccessors.includeInto(this)
 
  @::lazyAccessor 'crazyComputation', -> computeCrazyComputation()

Advised Accessors

Advised accessors allow you to call code before the reading or writing of a property value. If a property is being assigned, your advice function is called with the value being assigned and the old value.

class SpyStation
  @advisedAccessor 'online',
    get: -> @ensureAllSystemsNominal()
    set: -> @ensureUserIsSpy()
 
station = new SpyStation
station.online = true # ensures user is a spy, then assigns true 
station.online # ensures all systems are nominal, then returns true