Herança direta de javascript

Implementação:

var _with = function(proto, overrides) {
    if (!overrides) overrides = {};

    // that's the trick
    var ctor = function() { this.__proto__ = proto; };
    ctor.prototype = proto;
    var child = new ctor();
    // 'child'.[[Prototype]] pseudoproperty is set to 'proto' now
    // and real 'child.__proto__' property added

    for (var prop in overrides)
        if (overrides.hasOwnProperty(prop))
            child[prop] = overrides[prop];
    return child;
};

Exemplo de uso:

var Clazz = { 
    x: 10, 
    y: 20, 
    method: function() {
        return this.x;
    },
    method2: function() {
        return this.__proto__.x; // referencing parent
    }
};
var DerivedClazz = _with(Clazz, {x: 15});

var instance = _with(DerivedClazz);
alert(instance.y);         // 20
instance.x = 100;
alert(instance.x);         // 100
alert(instance.method());  // 100
alert(instance.method2()); // 15
alert(DerivedClazz.x);     // 15
alert(Clazz.x);            // 10

Conforme descrito aqui: http://tonsky.livejournal.com/244260.html