Use of global variable in node js

[SURAJ KUMAR CHANDRA]

How do you guys use node js vars.  Please refer to red marking. I am declaring variable at one place trying to use at another place, simply not working.

function login(email,password){ // Returns the login data row

  var email = email.trim().toLowerCase();

  var password = password.trim();

 var   result = [];  //Declaring here 

  //var queryString = "SELECT * FROM users where Email ="+"'"+email+"'"+ AND Password = +"'"+password+"'";

  var queryString = "SELECT * FROM users where Email ="+"'"+email+"' AND Password = '"+password+"'";

  //var execQuery = function execQuery(){

  con.query(queryString,function(err,rows){

  if(err) throw err;

 // console.log('Data received from Db:\n');

 //result = result.push('SUCCESS','0000','Data',rows)

 //console.log(rows);

result = rows;  // Want to use here

   //return rows;

});

 con.end(); 

//}

//console.log('Outside function block: '+execQuery());

return result; // want to see here

}

[Howard Dierking]

Based on a quick glance, it appears that the problem here has less to do with variable scope and more to do with your use of an async function (e.g. con.query). In the above, your function has likely exited before the callback has executed, meaning that result never has a chance to be set. Further, even if your callback did manage to execute, you can't just return it as though it's in the outer function's scope. You would need to execute a callback on the outer function or return a promise.

hth,

_howard

[Bruno Jouhier]

Callbacks are asynchronous! They are called after your function returns. The sequence is:

enter login function

con.execQuery initiates query

return from login function (result variable is still empty array)

later: 

node event loop invokes the callback

rows is assigned to result variable (too late, login returned before) 

[SURAJ KUMAR CHANDRA]

Hey Thanks Bruno,

Can you please alter this code? I have been fighting with user defined callback.

[Julia Y]

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[SURAJ KUMAR CHANDRA]

Thanks mate. But I am still finding it difficult to convert my above logic to make it async and return login data. I think I need to use multiple callback.

[endl...@gmail.com]

function login(email, password, callback){

    var email = email.trim().toLowerCase();
    var password = password.trim();

    var queryString = "SELECT * FROM users where Email ="+"'"+email+"' AND Password = '"+password+"'";

    con.query(queryString, function(err, rows){
        if(err){
            throw err;
        }
        callback(rows);
    });
};

login('skc...@gmail.com', 'Password', function(results){
    con.end();
    // Do stuff with results
});

[tpx1]

Hi,

I will mention that this piece of code has a big security issue.
You should never combine a sql query string with your parameter
directly. If email is a string like


' OR 1=1 --

you will login without any login information. For more information
see https://en.wikipedia.org/wiki/SQL_injection.

Use a sql library that supports sql prepared statements.

Another problem is that it seems so, that you store the password in
plain. You shouldn't do this in fact of security issues. Store passwords
as a hash and before querying the database, you hash the given password
two.

This post explains, how to do it in node.
http://lollyrock.com/articles/nodejs-sha512/

Thomas

Am 19.04.2017 um 13:59 schrieb endl...@gmail.com:
> function login(email, password, callback){
> var email = email.trim().toLowerCase();
> var password = password.trim();
>
> var queryString = "SELECT * FROM users where Email ="+"'"+email+"'
> AND Password = '"+password+"'";
>
> con.query(queryString, function(err, rows){
> if(err){
> throw err;
> }
> callback(rows);
> });
> };
>
> login('skc...@gmail.com', 'Password', function(results){
> con.end();
> // Do stuff with results
> });
>
> On Tuesday, March 28, 2017 at 5:58:47 AM UTC+5:30, SURAJ KUMAR CHANDRA
> wrote:
>
> How do you guys use node js vars. Please refer to red marking. I am
> declaring variable at one place trying to use at another place,
> simply not working.
>
> function login(email,password){ // Returns the login data row
> var email = email.trim().toLowerCase();
> var password = password.trim();
>

> var result = []; //*Declaring here*

>
> //var queryString = "SELECT * FROM users where Email
> ="+"'"+email+"'"+ AND Password = +"'"+password+"'";
> var queryString = "SELECT * FROM users where Email ="+"'"+email+"'
> AND Password = '"+password+"'";
>
> //var execQuery = function execQuery(){
> con.query(queryString,function(err,rows){
> if(err) throw err;
>
> // console.log('Data received from Db:\n');
> //result = result.push('SUCCESS','0000','Data',rows)
> //console.log(rows);

> result = rows; // *Want to use here*

> //return rows;
>
> });
>
> con.end();
>
> //}
> //console.log('Outside function block: '+execQuery());

> return result; /*/ want to see here*
> }
>
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