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());

//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) );  

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