Why does setting positions in a subclass of Array not change its length? Should I not subclass array?

Question

In the CoffeeScript program below, I create a subclass of Array which sets two positions in its constructor:

class SetPositionsArray extends Arr         


        

Answer 1

The following Array subclass, using node.js and implemented in coffeescript, works by using util.inherits & Object.defineProperty

util = require 'util'

class NGArray extends []
  constructor : ->

  util.inherits @, Array

  Object.defineProperty NGArray.prototype, "length",
    get: ->
      i = 0 
      for k,v of @
        i++ unless isNaN parseInt(k) 
      i

array = new NGArray()
array[0] = 'value'
array[1] = true
array[2] = ->
array[3] = 568
array.push(false)
array.pop()

console.log(array.length) #4