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) );