critical section in nodejs - writing data from frontend to json file

Question

I have following question that have I to synchronize requests when writing data to a file from multiple users in the same time. In java there is a synchronized keyword but I don't understand how it looks in nodejs.

app.post("/register",function(req,res){

      fs.readFile( __dirname + "/" + "users.json", 'utf8', function (err, data) {
      var users=JSON.parse(data);
      users["users"].push(req.body);
      var check=false;
      fs.writeFile(__dirname + "/" + "users.json", JSON.stringify(users),'utf8', function (err) {
         if(err){
            res.send(JSON.stringify("error"));
            check=true;
         }
      })
      if(!check){
         res.send(JSON.stringify("Created")); 
      }
           
   })
})

Answer 1

You should use writeFileSync instead of writeFile.

It returns nothing, so if the process went to the next line, this mean the file was written successfully!!