js面向对象的五种写法

//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) );