有无关键字new的区别

2024-10-21 05:10:35

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

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。

答案: A

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