javascript lesson 9 -- object oriented programming

when i was making a constructor in the previous lessons, i am infact making a new class.
A class can be thought of as a type, just like how 'number' and 'string' are types

when i made two objects bob and susan in previous lessons, they infact belong to class Person.

prototype keeps track of what a class can have property or method. the prototypes in javascript are automatically defined with a constructor.

*** if we want to add a method to class prototype, such that all the objects of this class can use the method. then we have to do this to extend the prototype
syntax:
classname.prototype.newmethod = function(){
            statements;
};

function Dog(breed){
this.breeds = breed;
}
Dog.prototype.bark = function(){
  console.log("woof");
};                                             // we added a bark method so other objects can use this method.

**Inheritance:
it allows one class to see and use the properties and methods of another class.

**DRY  -- Don't Repeat Yourself principle of programming.

** to inherit class1 properties to class2, we need to set the prototype of class2 to be class1.
ex:

// the original Animal class and sayName method
function Animal(name, numLegs) {
    this.name = name;
    this.numLegs = numLegs;
}
Animal.prototype.sayName = function() {
    console.log("Hi my name is "+this.name);
};

// define a Penguin class
function Penguin(name){
    this.name = name;
    this.numLegs = 2;
}

// set its prototype to be a new instance of Animal
Penguin.prototype = new Animal();

**the motif i noticed here is that to add any thing to a class like a method or inheritance of another class we use prototype.

* If javascript can't find something in the current class, it goes to the top of the prototype chain, to see if it from a class it inherited from.

This goes up the way upto the top Object.prototype . By default all classes directly  inherit from Object class, unless we change the class's prototype.