javascript - 当关联函数中的原型(prototype)值丢失时，函数会中断

Question

如何检查唐老鸭在“function inTheForest(object)”中是否有名称，并且如果它不显示警报(“未找到名称”)，然后继续显示约翰人的警报？

function Duck() {}

Duck.prototype.quack = function() {alert('Quaaaaaack!');};
Duck.prototype.feathers = function() {alert('The duck has white and gray    feathers.');};
//Duck.prototype.name = function() {alert('Donald Duck');};

function Person() {}

Person.prototype.quack = function() {alert('The person imitates a duck.');};
Person.prototype.feathers = function() {alert('The person takes a feather    from the ground and shows it.');};
Person.prototype.name = function() {alert('Rick James');};

function inTheForest(object) {
  object.quack();
  object.feathers();
  object.name(); 
}

function game() {
  var donald = new Duck();
  var john = new Person();
  inTheForest(donald);
  inTheForest(john);
}

game();

Answer 1

您可以通过typeof查看

像这样

if(typeof object.name === "undefined"){
  console.log("no name found")
}