[Solved] “callback is not defined” in node js

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Introduction

The “callback is not defined” error is a common issue encountered when working with Node.js. It occurs when a callback function is not defined or is not passed as an argument to a function. This error can be difficult to debug, as it can be caused by a variety of issues. In this article, we will discuss the causes of this error and how to solve it. We will also provide some tips on how to avoid this error in the future. By the end of this article, you should have a better understanding of how to debug and prevent this error.

Solution

The most likely cause of this error is that the callback function has not been defined. To fix this, you need to define the callback function before calling it. For example:

// Define the callback function
function myCallback(err, data) {
if (err) {
console.log(err);
} else {
console.log(data);
}
}

// Call the callback function
myFunction(myCallback);


You don’t need a callback in this case, because you’re at the end of your route, so to speak.

So instead, you could do something like handle it with sending an error message to your rendered page. 

var express = require('express');
var router = express.Router();
var mysql_db = require('../db/db_con')();
var pool = mysql_db.init();
/* GET home page. */
router.get("https://stackoverflow.com/", function(req, res, next) {
    pool.getConnection(function (err,conn) {
        if(err) {
            if(conn) {
                conn.release();
            }
            res.render('board',{rows: [],error:'Could not connect'});
        }else{
          var sql = "SELECT * FROM board";
          var exec = conn.query(sql,[] ,function(err, rows) {
              conn.release();
              if (err) throw err;
              res.render('board', { rows: rows });
        });
      }
    });
});

solved “callback is not defined” in node js


Solving the “callback is not defined” Error in Node.js

If you’re a Node.js developer, you’ve probably encountered the dreaded “callback is not defined” error. This error occurs when a callback function is not defined, or when the function is defined but not called. In this article, we’ll discuss what this error means and how to fix it.

What is a Callback Function?

A callback function is a function that is passed as an argument to another function. The callback function is then called by the other function when it has finished its task. This allows for asynchronous programming, which is a key feature of Node.js.

What Causes the “callback is not defined” Error?

The “callback is not defined” error occurs when a callback function is not defined, or when the function is defined but not called. This can happen for a variety of reasons, including:

  • The callback function is not defined.
  • The callback function is defined but not called.
  • The callback function is defined but not passed as an argument to the other function.
  • The callback function is defined but not called with the correct arguments.

How to Fix the “callback is not defined” Error

The first step in fixing the “callback is not defined” error is to make sure that the callback function is defined. If the callback function is not defined, you will need to define it before you can call it. Once the callback function is defined, you will need to make sure that it is called with the correct arguments.

If the callback function is defined but not called, you will need to make sure that it is called with the correct arguments. If the callback function is defined but not passed as an argument to the other function, you will need to make sure that it is passed as an argument. Finally, if the callback function is defined but not called with the correct arguments, you will need to make sure that it is called with the correct arguments.

Conclusion

The “callback is not defined” error is a common error in Node.js development. In this article, we discussed what this error means and how to fix it. We discussed what a callback function is and what causes the error. Finally, we discussed how to fix the error by making sure that the callback function is defined and called with the correct arguments.