// Sub classing array works as expected. Many people have false expectation that
// special behavior of number properties (sub[10]) is supposed to be inherited by a subclass.

function SubArray() {
  var subArray = Object.create(SubArray.prototype)
  Array.prototype.push.apply(subArray, arguments)
  return subArray
}
SubArray.prototype = Object.create(Array.prototype,
{ constructor: { value: SubArray }
, last: { value: function last() {
    return this[this.length - 1]
  }}
})