002 - 函数与类

一：函数

function factorial(n){return n<=1?1:n*factorial(n-1)}
	undefined
typeof factorial
	"function"
factorial(5)
	120

二：类

1. 定义一个构造函数

   function Point(x,y){this.x=x;this.y=y;}
   	undefined
   typeof Point
   	"function"

2. 使用new通过构造函数创建一个对象

   var point1 = new Point(1,2)
   	undefined
   typeof point1
   	"object"
   point1
   	Point {x: 1, y: 2}
   // 为类原型定义方法
   Point.prototype.distance = function(){return Math.sqrt(this.x*this.x+this.y*this.y)}
   	ƒ (){return Math.sqrt(this.x*this.x+this.y*this.y)}
   point1.distance()
   	2.23606797749979
   
   var point2 = new Point(3,4)
   	undefined
   point2.distance()
   	5
   // 对象重新构造
   point2.constructor()
   	undefined
   point2.x
   	undefined
   point2.constructor(4,5)
   	undefined
   point2.distance()
   	6.4031242374328485
   point2.x
   	4
   point2.y
   	5