两种常见JS面向象写法

基于构造函数

function Circle(r) { 
    this.r = r; 
} 
Circle.PI = 3.14159; 
Circle.prototype.area = function() { 
    return Circle.PI * this.r * this.r; 
} 

调用

var c = new Circle(1.0); 
console.log(c.area())//3.14159;

类Json写法

var Circle={ 
    "PI":3.14159, 
    "area":function(r){ 
        return this.PI * r * r; 
    } 
}; 

调用

console.log(Circle.area(1.0));//3.14159