JavaScript constructor and namespace in object literal style
I would suggest splitting the addition of the methods as follows:

myApp.model.Person.prototype.sayName = function () {
    alert(this.name);
};

myApp.model.Person.prototype.sayHi = function () {
    alert("Hi, " + this.name);
};


This way you can define additional methods in different places (if needed), as you're not replacing the entire prototype in one go.