JS 中面向对象的5种写法

//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) );