js面向对象的写法

首先 定义circle类，拥有成员变量r，常量PI和计算面积的成员函数area（）；

//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) );