functional js count ducks

bettersolution.js

  function duckCount() {
    return Array.prototype.slice.call(arguments).filter(function(obj) {
      return Object.prototype.hasOwnProperty.call(obj, 'quack')
    }).length
  }

  module.exports = duckCount

duckCount.js

function duckCount() {

    function isDuck(arg) {
        return Object.prototype.hasOwnProperty.call(arg, "quack")
    }

    function countDuck(args, index, number) {
        if (index >= args.length) {
            return number
        }
        else {
            return countDuck(args, index + 1, number + (isDuck(args[index]) ? 1 : 0))
        }
    }

    return countDuck(arguments, 0, 0)
}

module.exports = duckCount

function duckCount() {
return Array.prototype.filter.call(arguments, function(obj){
return Object.prototype.hasOwnProperty.call(obj, "quack");
}).length;
}

Thanks for posting this up! Take a look at my revision. maybe even better?