Js的五种面向对象写法

//第1种写法  
function Circle(r) {  
      this.r = r;  
}  
Circle.PI = 3.14159;  
Circle.prototype.area = function() {  
  return Circle.PI * this.r * this.r;  
}  
var c = new Circle(1.0);     
alert(c.area());  

//第2种写法  
var Circle = function() {  
   var obj = new Object();  
   obj.PI = 3.14159;  
     
   obj.area = function( r ) {  
       return this.PI * r * r;  
   }  
   return obj;  
}    
var c = new Circle();  
alert( c.area( 1.0 ) );  
 
//第3种写法  
var Circle = new Object();  
Circle.PI = 3.14159;  
Circle.Area = function( r ) {  
       return this.PI * r * r;  
}  
alert( Circle.Area( 1.0 ) ); 

//第4种写法  
var Circle={  
 "PI":3.14159,  
 "area":function(r){  
       return this.PI * r * r;  
  }  
};  
alert( Circle.area(1.0) );  

//第5种写法  
var Circle = new Function("this.PI = 3.14159;this.area = function( r ) {return r*r*this.PI;}");  
alert( (new Circle()).area(1.0) );