原型链题

function A () {

  }
  A.prototype.n = 1

  var b = new A()

  A.prototype = {
    n: 2,
    m: 3
  }

  var c = new A()
  console.log(b.n,b.m, c.n, c.m);//1 undefine 2 3

 /*
   测试题2
   */
  function F (){}
  Object.prototype.a = function(){
    console.log('a()')
  }
  Function.prototype.b = function(){
    console.log('b()')
  }
  
  var f = new F()
  f.a()
  // f.b() F的实例对象无法调用Function原型的方法
  F.a()
  F.b()