node.js - Mongoose查询回调返回？

Question

这是一个普遍问题，但是为什么 mongoose 查询会起作用，例如:

var myFunc = function(username, callback){
    User.findOne({username: username}, 'username name, password', function(err, user){
      callback(user);
    });
};

myFunc('somename', function(userInfo){
    console.log(userInfo);
});

需要另一个函数来返回用户吗？为什么我不能简单地:

var myFunc = function(username){
    User.findOne({username: username}, 'username name, password', function(err, user){
      return user;
    });
};

var userInfo = myFunc('somename');
console.log(userInfo);

Answer 1

As Node.js is executed in an asynchronous way sometimes it fails to get the result in userInfo if your query gets a long time.

Then for making sure that the userInfo value, you have to use callback or Promise.

有关 Node.js 异步性质的更多详细信息，您可以在此处查看

http://www.sohamkamani.com/blog/2016/03/14/wrapping-your-head-around-async-programming/] 1

https://blog.risingstack.com/node-hero-async-programming-in-node-js/