JS中面向对象的5种写法

//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));