functional js function spies

official solution.js

  function Spy(target, method) {
    var originalFunction = target[method]
    var result = {
      count: 0
    }

    target[method] = function() {
      result.count++
      return originalFunction.apply(target, arguments)
    }

    return result
  }

  module.exports = Spy

spies.js

function Spy(target, method) {
    var result = {count: 0}
    var originalMethod = target[method];

    target[method] = function () {
        result.count = result.count + 1
        return originalMethod.apply(target, Array.prototype.slice.call(arguments))
    }

    return result
}

module.exports = Spy

why is slice not needed?????

I have a question. Why use a class to hold the count? Can't we have Spy hold a variable count? Is it because we are returning it? If so, can't we have Spy to be a function that acts as a constructor and contains count as a variable in the class??