javascript面向对象的5种写法

定义Circle类，拥有成员变量半径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));