Node.js + Express - Callbacks returning undefined before Complete

You're returning your result as the first argument of your callback, but it's expected to be the second - in other words you're populating the err argument with your result, so the argument result will always be undefined.

So change:

function functionOne(callback) {              //QUERY TAKES A LONG TIME            client.query("[QUERY]", function(err, result) {                    callback(result);            });}

To this:

function functionOne(callback) {              //QUERY TAKES A LONG TIME            client.query("[QUERY]", function(err, result) {                    callback(null, result); // pass it as the second argument            });}

That should solve your issue.

this should work:

  //start execution  functionOne (functionTwo);     function functionOne(callback) {          //QUERY TAKES A LONG TIME        client.query("[QUERY]", function(err, result) {                callback(null, result);        });  }  function functionTwo(err, result) {       //call function done after long processing is finished with result         done(err,result);  }  function done(err,result){       //do your final processing here       console.log(result);  }

just change

client.query("[QUERY]", function(err, result) {                    callback(null, result);            });

to :

client.query("[QUERY]", function(err, result) {                    if( err) return callback(err);                    return callback(null, result);            });