Return a value from nested function

#1 
const shortUrlNumber = createShortUrlNumber();
console.log("Number RETURNED  " + shortUrlNumber);

function createShortUrlNumber() {
// create random number
  const shortNumber = Math.floor((Math.random() * 10) + 1);

// search database for any document with that shortNumber as key_url
  UrlConverter.findOne({ "key_url": shortNumber }, function (err, data) {
    if (err) {
      return handleError(err);
    } else if (data) {
      console.log("FOUND A DOCUMENT:  " + data);
      // call function again to create a new random number and search database
      createShortUrlNumber();
    } else {
      console.log("FOUND NONE: return shortNumber ");
      return shortNumber;
    }
  })
}

If I return shortNumber outside of UrlConverter.findOne() it never gets checked against the database.

I’m wondering how do I return shortNumber so that shortUrlNumber has that value?

#2

The problem isn’t actually when you find an unused number, it’s when you find a USED one and re-call createShortUrlNumber() again. If you find a number, you’re callling the function, but you aren’t returning the value of that nested call. Change that one line to:

return createShortUrlNumber();

and you should get what you’re expecting.

Of course, you realize you’re limiting yourself to exactly ten possible shortUrlNumbers? Just pointing out the obvious, but still.

#3

This did not solve the issue.

But I have noticed using console logs that the function is not completed before the returned value is trying to be used outside the createShortUrlNumber function.

If I console log shortUrlNumber after it’s set (line 2), the FOUND NONE console log happens after.

`
Number RETURNED undefined

FOUND NONE: return shortNumber
`
So now I think this must be an async process.

#4

I’ve had similar problems, without seeing more code it’s hard to suggest a way to help, but it probably is an async issue. That can be solved with Promises or await/async (but I haven’t really mastered those). What I had to do was really think about the order my code was executing. I read a quote somewhere that said something like
“javascript, like life, waits for no man”
So your your logs are right. I haven’t tested this but if you moved the log to here

} else {
      console.log("FOUND NONE: return shortNumber ");
      console.log("Number RETURNED  " + shortUrlNumber);
      return shortNumber;

I suspect Number RETURNED will not be undefined.

So if in your code you are trying to use shortUrlNumber immediately it won’t work because it is undefined.

You could maybe put a var shortUrlNumber in your function

function createShortUrlNumber() {
var shortUrlNumber;
// create random number
  const shortNumber = Math.floor((Math.random() * 10) + 1);

and then

} else {
      console.log("FOUND NONE: return shortNumber ");
      shortUrlNumber = shortNumber;
      //then do something with shortUrlNumber here
    }

But like I said this is untested and maybe Promises or await/async is the better route.

1 Like
#5

Since I posted this I rewrote the code to avoid the functional programming approach. I did a lot of if/else inside collection.find(), which is not what I wanted.
I am going to try and refactor to deal with the async aspect.
Might as well push myself into having a go.

#6