Convert call back to promise

Question

I am trying to convert one loopback callback function to promise, but I am not able to convert it. The code for is

let ds = app.datasources.ace_db
ds.connector.execute(sql,[],(err, data ) => {
   console.log('datalogger', data);
});

Is there any method to convert this peace of code to promise?

possible duplicate. check this question https://stackoverflow.com/questions/28432401/replacing-callbacks-with-promises-in-node-js — vader, Nov 21 '17 at 05:17
Related [github issue](https://github.com/strongloop/loopback/issues/418#issue-38984704) about Promise support in LoopBack. — Ivan Schwarz, Nov 21 '17 at 07:19
you can also use async npm package [link](https://www.npmjs.com/package/async) — Daniel, Nov 21 '17 at 10:55

score 3 · Answer 1 · answered Nov 21 '17 at 05:15

What you want to do is wrap your ds.connector.execute in a Promise, and return that Promise like so:

const dsConnectorPromise = function(sql, arr) {

    let p = new Promise((resolve, reject) => {

        ds.connector.execute(sql, arr, (err, data) => {

            if(err) reject(err);
            else resolve(data);
        });
    });

    return p; // return promise
};

You can then go on to use dsConnectorPromise like so:

dsConnectorPromise(sql, []).then(data => {

    console.log(data);

}).catch(err => console.log(err));

or you can just do `return new Promise((resolve, reject)...` without assigning to a `p` variable at all — nicholaswmin, Nov 21 '17 at 05:17

score 1 · Accepted Answer · answered Nov 21 '17 at 05:59

1

You could do a Promise.promisify()

let p = Promise.promisify(ds.connector.execute);
p(sql, []).then(...)

answered Nov 21 '17 at 05:59

Vasan

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Convert call back to promise

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