How to deal with returns in async javascript when callbacks are not an option?

Question

Of course, there are many async questions and answers. But my question is about an async situation in which I need to return something.

I have this in node express:

app.use('/', FalcorServer.dataSourceRoute(function(req, res) {
         return new someClass('SOMEHOST', req.query.paths);
}));

Now my problem is this, someClass is async because of AJAX. (in my example I use setTimeout to make my point).

Something like this:

class someClass {
    constructor(redisHost, pathString) {
        return setTimeout(function(){
            return someModel;
        }, 1500);
    }
}

module.
    exports = someClass;

But I have to deal with this return in my app.use, how can I do this?

Bang your head against the wall, because without callbacks, asynchronous code isn't going to work very well (read as "at all"). — Kevin B, Oct 08 '15 at 15:05
I'm guessing you've seen [this question](http://stackoverflow.com/questions/14220321/how-to-return-the-response-from-an-asynchronous-call). The answer is still the same really - you're still going to have to adjust your code to use a callback. Perhaps your constructor returns a function that takes a callback as an argument, and it's that function that calls `setTimeout`. — James Thorpe, Oct 08 '15 at 15:06
Ok thanks, any hints or directions where I could find a solution to this? — Bob van Luijt, Oct 08 '15 at 15:09
You could restructure this a bit. You could make the AJAX call *first* and then in the callback, call `app.use`. — gen_Eric, Oct 08 '15 at 15:10

score 1 · Accepted Answer · answered Oct 08 '15 at 15:27

I think you need to adjust your thinking ... app.use goes inside the callback. Without fully understanding all the full details of your issue I think this might help you.

function someClass(a, b, callback) {
  return setTimeout(function(){
    callback(a+b);
  }, 1500);
}

new someClass(1, 2, function(response) {
  console.log(response === 3);
  // your app.use statement which needs the response goes here.
  // In fact all your express (im guessing you are using express) stuff goes here
  // Example
  // app.use('/', FalcorServer.dataSourceRoute(function(req, res) {
  //    return response
  // }
});

Thanks, this helped, I know I would get some downvotes on this but I had to ask ... — Bob van Luijt, Oct 08 '15 at 17:25

How to deal with returns in async javascript when callbacks are not an option?

1 Answers1