How to use callbacks in module.export function for mysql query - nodejs,express

Question

I have the following code structure in exports.js

module.exports = {
    getData:function(param1,param2,callback){
        sql.query('SELECT users FROM table',function(error,result){
            callback(null,result[0]);
        });
    }
}

And I called it from main file app.js file like

var common = require('./exports');
console.log(common.getData(null,null));

I got the following error

TypeError: callback is not a function

However I found a similar question here. But didn't fixed the problem. Any help would be appreciated..!

You have this problem because callback is third argument of your function.. but when you call getData(null, null, <callback here>) you do not pass third argument. — Carmelo Catalfamo
– Carmelo Catalfamo, Commented Aug 2, 2017 at 11:04

Goolishka · Accepted Answer · 2017-08-02 10:48:49Z

1

if you want print results

var common = require('./exports');
common.getData(null, null, function(err, result){
    console.log(result)l
})

answered Aug 2, 2017 at 10:48

Goolishka

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1 Comment

Deepak M Over a year ago

Thanks for the help @Goolishka. But I can accept only one answer :)

Jonathan Goodman · Accepted Answer · 2017-08-02 10:59:46Z

0

getData() accepts 3 arguments

The last of which should be a function which you have not provided in your example. Add a callback function in your call like so:

common.getData(null,null, function(err, result) {

    console.log(result)

});

The sql.query function uses the callback function you pass in as the third parameter and thats why your getting the error to say it's missing.

edited Aug 2, 2017 at 10:59

answered Aug 2, 2017 at 10:51

Jonathan Goodman

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5 Comments

Deepak M Over a year ago

So I have to make a function to use the results right ? Is there a way to get only results without expanding a function like structure ?

Deepak M Over a year ago

For example consider this function test() { return "response"; } . When I call test() it will return response only. So I do not have to expand like ,let's say test(function(res){ // further }).

Jonathan Goodman Over a year ago

I've just updated my example. Yes you need to pass a function into common.getData. Thats the best way to handle the results.

Jonathan Goodman Over a year ago

Of course you can do what you've suggested in your comments but the thing about JavaScript is that if you have something thats happening Asynchronously the your return statement might be called before the async tasks has finished and then then return value might be wrong. Your callback function is only called at a time when the async task is complete.

Deepak M Over a year ago

Then I will go with this :D

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