JS面向对象

  //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) );