我在 Node js 和 Express 中有这个端点,它将学生添加到数组中。我在请求正文中传递了类名称和一组电子邮件。逻辑如下:
- 使用传递的类名搜索该类是否存在。如果该类存在,则遍历电子邮件数组,搜索具有该电子邮件的用户是否存在并具有 Angular 色成员。如果它们满足,则将它们添加到数组中。
问题:
- 当我尝试在循环内控制台记录数组时,它显示学生对象已添加到数组中。但是,当在循环之外时,我在 console.log 上得到一个空数组
这是我试图描述的实际代码:
const findClass = LessonClass.findOne({className: req.body.className}).exec();
findClass.then(classObject => {
// check that each emails exists and has role member
const studentArray = [];
const emailBody = req.body.email;
emailBody.forEach(email => User.findOne({email}).exec().then(userObject => {
if(userObject.role !== 'member'){
return res.status(400).send({
error: 'Only users with role member can be added to a class as students'
});
}
const student = {
email: userObject.email,
studentName: userObject.firstName + ' '+ userObject.lastName
};
// add the student to the student array
studentArray.push(student);
console.log(studentArray); // returns student object inside array
})
.catch(err => {
console.log(err);
}));
console.log(studentArray) //returns empty array
})
有人帮忙吗?
最佳答案
因为当您注销学生时,您的代码可能仍在添加学生,请参阅此代码
const findClass = LessonClass.findOne({ className: req.body.className}).exec();
findClass.then(classObject => {
// check that each emails exists and has role member
const studentArray = [];
const emailBody = req.body.email;
emailBody.forEach(email => User.findOne({email}).exec()
.then(userObject => {
if (userObject.role !== 'member') {
return res.status(400).send({
error: 'Only users with role member can be added to a class as students'
});
}
const student = {
email: userObject.email,
studentName: userObject.firstName + ' ' + userObject.lastName
};
// add the student to the student array
studentArray.push(student);
console.log(studentArray); // returns student object inside array
return studentArray;
})
.then(students => {
console.log(students);
}));
})
我所做的是,我删除了您的 console.log
并将其与第二个 then
链接起来,并从您的第一个 then
返回了学生数组。
在 javascript 中,回调是非阻塞的,即它们不会阻塞执行序列,并且控制将转到下一个语句。当您声明 studentsArray
并启动非同步操作(promise)时,它不会等待执行完成,而是直接进入 console.log
语句。
关于javascript - 无法在循环外访问数组元素,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/55263807/