Validador de Rut en Coffeescript

rutValidator.js

    formatRut = (str) ->
      str.replace(/\./g, '')

    checkRut = (str) ->

      if not str?
        return false

      str = str.toString().trim()
      str = formatRut str

      if not str.indexOf('-') is str.length - 2
        return false

      chars = new Array()
      serie = new Array(2, 3, 4, 5, 6, 7)
      dig = str.substr(str.length - 1, 1)
      rut = str.substr(0, str.length - 2)

      for i in [0..rut.length-1] by 1
        chars[i] = parseInt rut.charAt( (rut.length - 1 - i) )

      sum = 0
      k = 0
      resto = 0

      for j in [0..chars.length-1] by 1
        k = 0 if k == 6
        sum += parseInt(chars[j]) * parseInt(serie[k]);
        k++

      resto = sum % 11;
      dv = 11 - resto;
      dv = "K" if dv == 10
      dv = 0 if dv == 11

      dv.toString().trim().toUpperCase() == dig.toString().trim().toUpperCase()