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I'm using nodeJs express 3 framework with postgreSQL, I'm using the script below to look for a username in DB and populate a variable so I can pass it to my view. Here is my script :

app.js
var app = express();
app.use(express.bodyParser());
......
function fncCheckUsernameAvailability(vstrUsername){
    var pg = require("pg");
    var client = new pg.Client({user: 'xxx', password: 'xxxx', database: 'xxx', host: 'example.com'});
    var response = "";
    client.connect(function(err) {
  if(err) {
    return console.error('could not connect to postgres', err);
  }
 client.query("SELECT username FROM users WHERE username ='"+vstrUsername+"'", function(err, result) {
    if(err) {
      return console.error('error running query', err);
    }
        if(result.rows[0] == undefined){
            //console.log("Username available");
            response = "Username available";//Populating The variable here
        }else{
            //console.log("Username already taken");
            response = "Username already taken";//Populating The variable here
        }
    client.end();
  });
    });
    return response;
}


app.post("/Signup", function(req, res){
var username = req.body.username;
var Response = fncCheckUsernameAvailability(username);
console.log(Response);
}

The response variable is allways "undefined", so how can I make that script waiting until the DB checking is done to populate the "response" variable?

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1 Answer

up vote 1 down vote accepted

You cannot place return values into asynchronous functions. You would instead need to use a callback, and this is what your code might look like:

function fncCheckUsernameAvailability(vstrUsername, callback) {
  client.connect(function(err) {
    if (err) {
      callback(err, null);
      return;
    }

    client.query("SELECT username FROM users WHERE username ='" + vstrUsername + "'", function (err, result) {
      client.end();
      if (err) {
        callback(err, null);
        return;
      }

      if (result.rows[0] == undefined) callback(null, 'Username available.');
      else callback(null, 'Username taken.');
    });
  });
};

You would use the function like this:

app.post("/Signup", function(req, res) {
  var username = req.body.username;
  fncCheckUsernameAvailability(username, function(err, result) {
    console.log(result);
  });
});
share|improve this answer
    
Hi, thanks for the answer but it returs "null" everytime. –  OussamaLord Sep 13 '13 at 20:24
1  
What does err contain? Put a console.log(err) before the console.log(result) and post what it contains. –  hexacyanide Sep 13 '13 at 20:26
    
Hi, really sorry I made a mistake in my table's name , now it is working perfect, thanks. –  OussamaLord Sep 13 '13 at 20:37
    
Hi, this is working fncCheckUsernameAvailability(username, function(err, result) {console.log(result);}); it prints on console but this fncCheckUsernameAvailability(username, function(err, result) {myVar = result;}); will not populate my variable is it something asynchrounous too? –  OussamaLord Sep 13 '13 at 21:07
    
It will populate the variable as long as it is within the callback. If it is null then you probably have an error somewhere. –  hexacyanide Sep 13 '13 at 21:12
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