1.sample o-o class 

function obj(){}
obj.prototype.showLog = function(str){
console.log(str);
};


var o = new obj();
o.showLog("something");

2.prototype defination will be override by object instance method or prop

function obj(){
this.m = function(){console.log("obj version");}
}
obj.prototype.m = function(){console.log("prototype version");}


var o = new obj();
o.m();

This reason is because the init sequence :


1 Object members 
2 prototpe methods or properties
3 Object methods 

3.typeof , instanceof , constructor usage

function obj(){}
var o = new obj();


console.log(typeof o );


console.log(o instanceof obj);
console.log(o.constructor);

4.object clone 

function obj(){}
var o = new obj();


var o2 = new o.constructor();//very important when we do not know the type


console.log(o2 instanceof obj);
console.log(o == o2);

5.inheritance

function parent(){}
parent.prototype.show = function(msg){console.log(msg);}
function child(){};
child.prototype.show = parent.prototype.show;
var c  = new child();
c.show("hello");

problem :

console.log(c instanceof parent);


result is False!!!

To Fix the Issue , Version 2 :

function parent(){}
parent.prototype.show = function(msg){console.log(msg);}
function child(){};
child.prototype = new parent();
child.prototype.showEx = function(msg){console.log("from showEx " + msg);}
var c = new child();
c.show("hello");
c.showEx("hello");

6.Html Element prototype

prepare HTML : 
<div id="parent">
<div id="a">I'm going to be removed.</div>
</div

Javascript :

HTMLElement.prototype.remove = function (){


if(this.parentNode)
{
this.parentNode.removeChild(this);
}


}


console.log(document.getElementById("a").remove());

7.Extend Array 

function list (){}
list.prototype = new Array();
list.prototype.add = function(){for(var i = 0;i < arguments.length;i++)this.push(arguments[i]);}
list.prototype.remove = function(n){for(var i =0 ; i < this.length;i++) if(this[i] == n){this.splice(i,1);}}


var l = new list();
l.add(1,2,3,4);
l.remove(3);


console.log(l);

8.Extend Number Class

Number.prototype.add = function(){var result = 0; for(var i = 0 ;i < arguments.length;i++) result += arguments[i]; return result;};
var n = 5;


console.log(n.add(5,2,3,4,9));