Returning values from nested functions in Javascript [duplicate]

Question

Consider this code (shortened)

function getSecret() {
    db.transaction(
        function (transaction) {
            transaction.executeSql(
                'SELECT * FROM table LIMIT 1;',
                null,
                function(transaction, result) {
                    var row = result.rows.item(0);
                    var secret = row.secret;
                    return secret;
                }, errorHandler
            );
        }
    )
}

How would I return the value of secret to the main function? I have read this answer Return value from nested function in Javascript

And tried this

function getSecret() {
    db.transaction(
        function doSql(transaction) {
            transaction.executeSql(
                'SELECT * FROM table LIMIT 1;',
                null,
                function(transaction, result) {
                    var row = result.rows.item(0);
                    var secret = row.secret;
                    return secret;
                }, errorHandler
            );
        }
    )
    return doSql;
}

However this did not work.

Thanks!

Sarfraz · Accepted Answer · 2010-07-30 17:28:47Z

4

Try:

function getSecret() {
    var secret = '';

    db.transaction(
        function (transaction) {
            transaction.executeSql(
                'SELECT * FROM table LIMIT 1;',
                null,
                function(transaction, result) {
                    var row = result.rows.item(0);
                    secret = row.secret;
                }, errorHandler
            );
        }
    )

  return secret;
}

answered Jul 30, 2010 at 17:28

Sarfraz

384k81 gold badges561 silver badges613 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Pointy Over a year ago

Is the database operation not asynchronous? I'm pretty sure that it is, and that therefore the solution here cannot possibly work. The "success" callback function is called when the query completes, while the outer function will return immediately after the query is started.

Black Over a year ago

did this 'asynchronous' issue ever get answered?

Manish Agrawal Over a year ago

i also have this problem. have you solved this problem if yes then plz share thanks. - Pointy and Pete Shaw

Daniel Le'Sage · Accepted Answer · 2016-11-08 06:15:12Z

3

Try promisifying the database operation before returning your payload.

Additionally, you can use promise's built in reject() as an error handler, returning the transaction object whenever the function returns undefined.

Declare promise within function:

function getSecret() {
    var secret = '';
    return new Promise(function(resolve, reject) {
        db.transaction(
            function(transaction) {
                transaction.executeSql(
                    'SELECT * FROM table LIMIT 1;',
                    null,
                    function(transaction, result) {
                        if (typeof(result) === 'undefined') {
                            var row = result.rows.item(0);
                            secret = row.secret;
                            resolve(secret)
                        },
                        else {
                            reject(transaction)
                        }
                    }
                );
            }
        )
    })
}

Then call the function.

//If function resolves, log the secret. 
//if function rejects, log the transaction
getSecret().then(function(secret) {
    console.log(secret);
})
.catch(function(err) {
    console.log('Error in db.transaction ' + err)
})

Hope that helps.

answered Nov 8, 2016 at 6:15

Daniel Le'Sage

1063 bronze badges

1 Comment

Tigerrrrr Over a year ago

In my opinion, this is the "correct" answer.

Fletcher Moore · Accepted Answer · 2010-07-30 17:31:42Z

1

function getSecret() {
    var retval = undefined; // or a reasonable default
    db.transaction(
        function doSql(transaction) {
            transaction.executeSql(
                'SELECT * FROM table LIMIT 1;',
                null,
                function(transaction, result) {
                    var row = result.rows.item(0);
                    var secret = row.secret;
                    retval = secret;
                }, errorHandler
            );
        }
    )
    return retval;
}

This will create a closure over the retval variable. When transaction is called, retval will be updated.

answered Jul 30, 2010 at 17:31

Fletcher Moore

13.9k11 gold badges43 silver badges59 bronze badges

1 Comment

Pointy Over a year ago

This will not work. The callback function from the query is executed asynchronously, while the return from getSecret() will happen immediately after the transaction is started.

Collectives™ on Stack Overflow

Returning values from nested functions in Javascript [duplicate]

3 Answers 3

3 Comments

1 Comment

1 Comment

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

1 Comment

1 Comment

Linked

Related