Dollarize helper in Coffeescript

dollarize.coffee

dollarize = (n, currency = "$", decimals = 2,
    decimalSeparator = ".", thousandsSeparator = ",") ->

  if n instanceof String
    n = parseInt n, 10

  sign = if n < 0 then "-" else ""

  wholeDigits = "" + Math.abs(n - (n % 1))

  postThousands = if wholeDigits.length > 3 
    wholeDigits.length % 3 
  else 
    0

  higherDigits = if postThousands > 0
    wholeDigits.substr(0, postThousands) + thousandsSeparator
  else
    ""

  middleDigits = wholeDigits.substr(postThousands).replace(/(\d{3})(?=\d)/g, "$1" + thousandsSeparator)

  decimalDigits = if decimals
    decimalSeparator + Math.abs(n % 1).toFixed(decimals).substr(2)
  else
    ""

  currency + sign + higherDigits + middleDigits + decimalDigits


dollarize(-1234567.89) => $-1,234,567.89