SubArray.js

// 20111028 jorge@jorgechamorro.com
// How to subclass Array
// In reply to https://gist.github.com/1100841/9c959db9314338a09c0f288c2c0ca5553816e400

function subArray () {
  var nu = Array.prototype.slice.apply(arguments); // @grimen: Fixed to support `new Array(666)` (=> `[666]` instead of Array of size 666)
  nu.__proto__= subArray.prototype;
  return nu;
}

subArray.prototype= {
  __proto__: Array.prototype,
  custom: function () { return "custom" }
}

/*
o= new subArray(1,2,3)
[ 1, 2, 3 ]

o instanceof Array
true

o instanceof subArray
true

o.custom()
'custom'

o.length
3

o.length=5, o
[ 1, 2, 3, ,  ]

o.length=2, o
[ 1, 2 ]

o.push(3), o
[ 1, 2, 3 ]

...etc
*/