JS 中面向对象的5种写法

//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());

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//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 ) );

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