async

async

async.waterfall([
      getDbHandle,
      function(args, cb){
        connection = args.connection;

        args = {
          connection: connection,
          email: req.body.email
        };
        cb(null, args);
      },
      User.isEmailExist,
      function validateInput (cb) {
        var check = require('validator').check;

        try {
          check(req.body.email, 'email_invalid').isEmail();
          var args = {
            connection: connection,
            email: req.body.email,
            displayName: req.body.displayName,
            password: req.body.password
          };
          cb(null, args);
        } catch (e) {
          cb(e.message);
        }
      },
      User.add
    ], function (status) {
        res.send({status:status});
        releaseDbHandle(connection);
    });