JavaScript 中的对象如何传递到 for...in 循环中？

Question

我是 JavaScript 新手，现在正在学习 for...in 循环和对象。我正在用下面的例子练习：

let spaceship = {
    crew: {
    captain: { 
        name: 'Lily', 
        degree: 'Computer Engineering', 
        cheerTeam() { console.log('You got this!') } 
        },
    'chief officer': { 
        name: 'Dan', 
        degree: 'Aerospace Engineering', 
        agree() { console.log('I agree, captain!') } 
        },
    medic: { 
        name: 'Clementine', 
        degree: 'Physics', 
        announce() { console.log(`Jets on!`) } },
    translator: {
        name: 'Shauna', 
        degree: 'Conservation Science', 
        powerFuel() { console.log('The tank is full!') } 
        }
    }
}; 

for (let crewMember in spaceship.crew){
  console.log(`${crewMember}: ${crewMember.name}`);
}

此代码的输出是控制台成功记录了crewMember，但没有记录crewMember.name。如图所示，crewMember.name 未定义。 另一方面，当我将日志语句更改为：

for (let crewMember in spaceship.crew){
  console.log(`${crewMember}: ${spaceship.crew[crewMember].name}`);
}

机组人员姓名已成功登录。我不明白为什么我能够在console.log语句的前半部分不通过spaceship.crew来访问船员，但在后半部分我必须通过spaceship.crew。

Answer 1

正如评论中所说。

for in

循环获取属性名称作为

key

。所以它是

captain

或

'chief officer'

的占位符。您可以通过点符号和括号符号访问属性。使用变量时使用括号：

所以：

spaceship.crew[crewMember]

这应该可行。参见示例：

let spaceship = {
    crew: {
    captain: { 
        name: 'Lily', 
        degree: 'Computer Engineering', 
        cheerTeam() { console.log('You got this!') } 
        },
    'chief officer': { 
        name: 'Dan', 
        degree: 'Aerospace Engineering', 
        agree() { console.log('I agree, captain!') } 
        },
    medic: { 
        name: 'Clementine', 
        degree: 'Physics', 
        announce() { console.log(`Jets on!`) } },
    translator: {
        name: 'Shauna', 
        degree: 'Conservation Science', 
        powerFuel() { console.log('The tank is full!') } 
        }
    }
}; 

for (let crewMember in spaceship.crew){
  console.log(`${crewMember}: ${spaceship.crew[crewMember].name}`);
}