How can i pass parameter in callback function node.js?

Question

var data = {};
data = connection.query(sql, [ori_image_path[i], src_image_path[i], title], function(err, results) {
  if (err) {
    console.dir(err);
    data["error_message"] = "failed";
    return data;
  }
})

if (i == ori_image_path.length - 1) {
  if (data["error_message"] === undefined) data["success_message"] = "이미지 업로드 완료";
  res.send(data);
}

I want to use variable data like this.

But variable data not changed!

always variable data = {}

I don't know javascript well...

How can I use variable data to detect errors? Could you help me?

connection.query is asynchronous, data does change but not when you want it to — Lawrence Cherone
– Lawrence Cherone, Commented May 19, 2021 at 15:51

Charlie · Accepted Answer · 2021-05-19 15:45:38Z

1

Hello you need to set result to data in callback function like this

var data = {};
connection.query(sql, [ori_image_path[i], src_image_path[i], title], function(err, results){
    if(err){
        console.dir(err);
        data["error_message"] = "failed";
    }
    data = results;
    return data;
});

also you need to try

if(typeof data["error_message"] === 'undefined')

instead of

if(data["error_message"] === undefined)

edited May 19, 2021 at 15:45

Charlie

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answered May 19, 2021 at 15:29

Dolgoon Doodii

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2 Comments

Leftddr Over a year ago

thank you, i want to variable data to use for detect error in sql execution, but variable data does not change. variable data is always = {} . In your code, can I set in variable data "error_message" and can i use this, outside of callback function?

Dolgoon Doodii Over a year ago

Hi, I think you can't use, it's because Javascript running your if(typeof data["error_message"] === 'undefined') condition before data has property error_message. Method 1: Put everything in callback Method 2: Use await

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