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) );