[Kolyaj]

function mixin(dst) {
    for (var i = 1; i < arguments.length; i++) {
        for (var prop in arguments[i]) {
            if (arguments[i].hasOwnProperty(prop)) {
                dst[prop] = arguments[i][prop];
            }
        }
    }
    return dst;
}

Function.prototype.inherit = function(proto) {
    var that = this;
    proto = proto || {};
    var constructor = proto.hasOwnProperty('constructor') ? proto.constructor : function() { that.apply(this, arguments); };
    var F = function() {};
    F.prototype = this.prototype;
    constructor.prototype = mixin(new F(), proto);
    constructor.superclass = this.prototype;
    constructor.prototype.constructor = constructor;
    return constructor;
};

// ===============================================

var A = Object.inherit({
    constructor: function(foo) {
        this.foo = foo;
    },

    alert: function() {
        alert(this.foo);
    }
});

var B = A.inherit({
    constructor: function(foo) {
        B.superclass.constructor.apply(this, arguments);
        this.bar = foo + 1;
    },

    alert: function() {
        B.superclass.alert.apply(this, arguments);
        alert(this.bar);
    }
});

var b = new B(1);
b.alert();

Например.