An alternative to $scope.$watch

efficientWatch.js.coffee

'use strict'
#Usage:
# efficientWatch.watch 'someProperty', ctrl, (newValue, oldValue) ->
#    console.log("As good as $scope.$watch, without the digest tax!")

#Source: http://www.jomendez.com/2015/02/25/optimizing-code-object-defineproperty-scope-watch-angularjs/
#With my own changes:
# 1.) The attribute name is generic
# 2.) The callback function (3rd parameter) is passed with the oldValue as the second parameter, to mimic $scope.$watch better.

efficientWatch = () ->
  watch = (name, controller, callback) ->

    #Supported by IE9 and up. What the heck, IE is dead anyway.
    Object.defineProperty controller, name,
      get: () ->
        attribute_name = "_" + name
        return this[attribute_name]
      set: (newValue) ->
        attribute_name = "_" + name
        oldValue = this[attribute_name]
        this[attribute_name] =  newValue

        if typeof callback == 'function'
          #mimic $scope.$watch
          callback(newValue, oldValue)

  service =
    watch: watch

  service

efficientWatch.$inject = []

angular
  .module('appServices')
  .factory 'efficientWatch', efficientWatch
return