Javascript callback function error

Question

For some reason the code I wrote below(an POST route I was making) is not exactly working how I thought it would.

app.post("/", function (req, res, error) {
  var message = "";
  tableSvc.createTable("tableName", function (error, result,response){
      if (error) 
        message += "There was an error in creating this table";
      else 
        message += "Table created succesfully";

  }); 
  console.log(message);     
});

Instead of printing "There was an error..." or "Table created..." , the code above only prints out an empty string.
I know that the call-back function is being executed because if I put console.log(message) inside of the call-back function, then either of the above two strings does get printed to the console.
I am new to Javascript and call-functions, so why isn't my code executing the way I intended it to?

Answer 1

消除了我的猜测-错过了您关于执行回调的要点-这很可能是其他回复提供的异步问题。

Answer 2

I think the scope of variable message is the problem here. I have not tried this but may work.

 app.post("/", function (req, res, error) {
    var obj = this;
    obj.message = '';
      tableSvc.createTable("tableName", function (error, result,response){
          if (error) 
            obj.message += "There was an error in creating this table";
          else 
            obj.message += "Table created succesfully";

      }); 

      while(obj.message.length===0){
            ;//Block the next execution till the operation above is complete.
      }


      console.log(obj.message);     
    });