function is running before sql query is finished, node js

Question

i have made an event listener for my server which listens for when someone is trying to log on, so i do an sql query and then if the info matches, it logs them on. problem is, its testing if the info matches before it runs the query so it will always return false. here is my code

player.on('checkLogin', function(data)
{   
    var logIn = "";
    connection.query({
    sql: "SELECT * FROM users WHERE username = ?", 
    values: [data.user] },


    function(error, results, fields) 
    {                                               
        if (error) 
        { 
            console.log(error); 
        }

        if(results) 
        {   
            var pass = "";  

            for (i = 0; i < results.length; i++)
            {
                pass = (results[i].password);
            }

            var input = crypto.createHash('md5').update(data.pass).digest("hex");

            if (pass == input)
            {
                logIn = true;
            }                       
        }
    });

    if (logIn == true)
    {
        this.em.emit('login', 
            {
            id: player.playerid 
            });
    }
}.bind(this));

I heard promises will fix this but is there any easy way around this?, thanks in advance

This question gets asked all the time. You need to reply inside the callback. Simply replace logIn = true; with whatever code you wanted to run at the bottom. — user5734311
– user5734311, Commented Feb 16, 2017 at 23:40
i get the error "cannot read property 'emit' of undefined" when it tries to log in — Rachel Dockter
– Rachel Dockter, Commented Feb 16, 2017 at 23:43

Nico · Accepted Answer · 2017-02-16 23:47:21Z

1

The issue you have is your if(login == true) is outside of the completion handlers of the query.

Move the if(logIn == true) into your completion handler.

player.on('checkLogin', function(data)
{   
    var logIn = "";
    connection.query({
    sql: "SELECT * FROM users WHERE username = ?", 
    values: [data.user] },


    function(error, results, fields) 
    {                                               
        if (error) 
        { 
            console.log(error); 
        }

        if(results) 
        {   
            var pass = "";  

            for (i = 0; i < results.length; i++)
            {
                pass = (results[i].password);
            }

            var input = crypto.createHash('md5').update(data.pass).digest("hex");

            if (pass == input)
            {
                logIn = true; //<-- could just handle it here.
            }
            if (logIn == true) //<-- moved inside completion handler
            {
               //log on
            }                       
        }
    });


}.bind(this));

Now the reason it is being called is your connection.query runs asynchronously which is why the function handler is used. Code outside the completion handler will be run immediately.

EDIT from Additional Changes

Based on your changes your this scope will be changed when moved inside the completion handler function. To get a reference back you will need a reference to the player scope (assuming that is what this is). So that can be handled simply by creating a variable of this as var that = this; at the top of your checklogin function. Something like:

player.on('checkLogin', function(data)
{   
    var that = this; //create a variable to store the scope (this)
    var logIn = "";
    connection.query({
    sql: "SELECT * FROM users WHERE username = ?", 
    values: [data.user] },


    function(error, results, fields) 
    {                                               
        if (error) 
        { 
            console.log(error); 
        }

        if(results) 
        {   
            var pass = "";  

            for (i = 0; i < results.length; i++)
            {
                pass = (results[i].password);
            }

            var input = crypto.createHash('md5').update(data.pass).digest("hex");

            if (pass == input)
            {
                logIn = true; //<-- could just handle it here.
            }
            if (logIn == true) //<-- moved inside completion handler
            {
               //log on
              that.em.emit('login',  //<-- reference `that` not `this`
              {
                 id: player.playerid 
              });
            }                       
        }
    });


}.bind(this));

edited Feb 16, 2017 at 23:47

answered Feb 16, 2017 at 23:40

Nico

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6 Comments

Rachel Dockter Over a year ago

then i get the error "cannot read property 'emit' of undefined" when it tries to log in

Rachel Dockter Over a year ago

oh sorry yes ill include it

Nico Over a year ago

@RachelDockter thanks for the update.. I have provided an edit

Nico Over a year ago

Did you at the var that = this; at the top?

Rachel Dockter Over a year ago

i just did and it works now, thankyou very much :):)

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