[danik.js]

function Base() { }
Base.prototype.method1 = function(params) {/*...*/};
Base.prototype.method2 = function(params) { alert('base method'); };

function Extended() { }
Extended.prototype = Object.create(Base.prototype);
Extended.prototype.method2 = function(params) {
    alert('extended method');
    Base.prototype.method2.apply(this, arguments);
};

var instance = new Extended();
instance.method2();