subclass_natives_in_node.js

var assert = require('assert')

  , subclass = function(type, proto){
      // make sure we are extending a global constructor
      // accepted: [Boolean, Number, String, Array, Object, Function, RegExp, Date]
      if(!global[type.name] || global[type.name].name != type.name) throw new Error();

      var constructor = proto.constructor,
          keys = Object.keys(proto),
          Obj = process.binding('evals').Script.runInNewContext('x = '+type.name), // eval ftw
          obj = function(){
            var instance = new Obj();
            if(constructor) constructor.apply(instance, arguments);
            return instance;
          };
          obj.prototype.__proto__ = type.prototype; // passes instanceof 'type'
          Obj.prototype.__proto__ = obj.prototype; // passes instanceof 'this'

      for(var i=0,l=keys.length; i<l; i++){
        if(keys[i] != 'constructor') Obj.prototype[keys[i]] = proto[keys[i]]; 
      }
      return obj;
    }

  , SpecialArray = subclass(Array, {
      constructor: function(){
         Object.defineProperty(this, 'special', {
           value: 'special',
           enumerable: false
         });
      },
      test: function(){}
    })
    
  , arr = []
  , sa = new SpecialArray();

// very strict, instance constructor === Array.constructor
assert.ok(Array.isArray(sa)); 
// still passes instanceof Array tests
assert.ok(sa instanceof Array);
// still has unique identity 
assert.ok(sa instanceof SpecialArray);
// should be extended
assert.ok(typeof sa.test == 'function');
// this should not
assert.ok(typeof arr.test == 'undefined');
// pass other hardcore type checks
assert.ok(Object.prototype.toString.call(sa) == '[object Array]');
// make sure constructor works
assert.ok(sa.special == 'special');
assert.ok(sa.propertyIsEnumerable('special') == false);
// make sure length property still works
assert.ok(sa.push(1,2,3) == 3);
assert.ok(sa.push(4,5) == 5);
assert.ok(sa.length == 5);
// check JSON.stringify()
assert.ok(JSON.stringify(sa) == '[1,2,3,4,5]');