Return value from callback in function

Question

Hello i would like to return a simple Boolean with there options: - true: user exists in database - false: user doesn't exists in database

Here's my non-working code:

database.users.get("test-username", function (err, value) {
    if (err) {
        return err;
    } else {
        return value;
    }
})

The return is always undefined I know that NodeJS is designed to work async, but async functions don't allow me to return something. I'm stuck, please help!

Also, i use LevelUP as database system. (if my problem have no solution, is there an other database system in NodeJS that allow synchronous?)

Thanks to the community!

Leon · Accepted Answer · 2017-05-27 14:10:52Z

5

Do you get anything back when you console.log your return? for example:

function dbCall(){    
database.users.get("test-username",function(err, value){
     if(err){
          return false;
     }else{
         console.log(value);
         return value;
     }
}
}

if you get something in value then the reason you don't see anything in return is because the api call is asynchronous. You'll have to make a promise.

new Promise(resolve,reject){
    let data = dbCall();
    if(data == false)
         reject(data);
    else
         resolve(data);
}

answered May 27, 2017 at 14:10

Leon

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3 Comments

L.X Over a year ago

Sure, console.log works in callback, outside the callback nothing works. I found another solution, is to call function with req and res parameters (ExpressJS), so i can display response directly with res.send(response) in callback

Leon Over a year ago

The reason it doesn't work is because your program does not wait for a async call to be called back before continuing. But yes req and res should work too :) However is you do need to do more complicated operations using the data, I highly recommend you look up promises and async js library.

L.X Over a year ago

Yes, i finally used Promise Thanks for your help!

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