选择篇(022)-下面代码的输出是什么?

function Person(firstName, lastName) {
  this.firstName = firstName;
  this.lastName = lastName;
}

const lydia = new Person("Lydia", "Hallie");
const sarah = Person("Sarah", "Smith");

console.log(lydia);
console.log(sarah);

• A: Person {firstName: "Lydia", lastName: "Hallie"} and undefined
• B: Person {firstName: "Lydia", lastName: "Hallie"} and Person {firstName: "Sarah", lastName: "Smith"}
• C: Person {firstName: "Lydia", lastName: "Hallie"} and {}
• D:Person {firstName: "Lydia", lastName: "Hallie"} and ReferenceError

答案: A

对于sarah，我们没有使用new关键字。使用new时，它指的是我们创建的新空对象。但是，如果你不添加new它指的是全局对象！

我们指定了this.firstName等于'Sarah和this.lastName等于Smith。我们实际做的是定义global.firstName ='Sarah'和global.lastName ='Smith。 sarah本身的返回值是undefined。