can't update document before next request

hi.

i'm using some code like this:

user.findFlag in initial is 1

```javascript

db.User.find({ _id: 1}, (err, user) => {
if(user.findFlag === 1){

// do some other things

db.User.findOneAndUpdate(
{ _id: 1 },
{ findFlag: 0}, { upsert: true }, (err, user) => {
if (err) return callback(err)

callback(null, user)
});
}
else if(user.findFlag === 0){
db.User.findOneAndUpdate(
{ _id: 1 },
{ findFlag: 1}, { upsert: true }, (err, user) => {
if (err) return callback(err)

callback(null, user)
});
}
})
```

if client request more than one time without delay, user.findFlag doesnt change and just
**if(user.findFlag === 1)** excuted.
i know it is because of async but how to fix it?

nodejs: 8.3.0, express 4.15.4, mongoose 4.11.9

Start by reproducing the reported behavior through the db.User.find and db.User.findOneAndUpdate callbacks using the stated Node.js, Express, and Mongoose versions. Check how overlapping client requests observe findFlag, then define and verify the expected result for repeated requests; the payload names no repository files or tests.

Written by the indexing model from the issue text.