All new properties and methods of the subclass must come after the assignment of the prototype property : Inheritance « Object Oriented « JavaScript Tutorial

1. JavaScript Tutorial
2. Object Oriented
3. Inheritance

function SubClass() {
}

SubClass.prototype = new BaseClass();

SubClass.prototype.name = "";
SubClass.prototype.sayName = function () {
    alert(this.name);
};
var objA = new BaseClass();
var objB = new SubClass();
objA.color = "red";
objB.color = "blue";
objB.name = "MyName";
objA.sayColor();
objB.sayColor();
objB.sayName();