JS 面向对象的5钟写法

Java代码

//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

//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

//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

//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

//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) ); 

大家来讨论一下这五种写法，它们的优缺点，哪个比较规范，特别是最后两种，经常见到。