JS 中面向对象的五种写法

//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()

Java代码

1. //第1种写法??? ??
2. function Circle(r) {??? ??
3. ??????this.r = r;??? ??
4. }??? ??
5. Circle.PI = 3.14159;??? ??
6. Circle.prototype.area = function() {??? ??
7. ??return Circle.PI * this.r * this.r;??? ??
8. }??? ??
9. ?? ??
10. var c = new Circle(1.0);?????? ??
11. 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());

?

Java代码

1. //第2种写法??? ??
2. var Circle = function() {??? ??
3. ??? var obj = new Object();??? ??
4. ??? obj.PI = 3.14159;??? ??
5. ?????? ??
6. ??? obj.area = function( r ) {??? ??
7. ???????return this.PI * r * r;??? ??
8. ??? }??? ??
9. ???return obj;??? ??
10. }??? ??
11. ?? ??
12. var c = new Circle();??? ??
13. 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 ) );

?

Java代码

1. //第3种写法??? ??
2. var Circle = new Object();??? ??
3. Circle.PI = 3.14159;??? ??
4. Circle.Area = function( r ) {??? ??
5. ???????return this.PI * r * r;??? ??
6. }??? ??
7. ?? ??
8. 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 ) );

?

Java代码

1. //第4种写法??? ??
2. var Circle={??? ??
3. ???"PI":3.14159,??? ??
4. "area":function(r){??? ??
5. ??????????return this.PI * r * r;??? ??
6. ???????? }??? ??
7. };??? ??
8. 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) );

?

Java代码

1. //第5种写法??? ??
2. var Circle = new Function("this.PI = 3.14159;this.area = function( r ) {return r*r*this.PI;}");??? ??
3. ?? ??
4. alert( (new Circle()).area(1.0) );????