gistfile1.js

var connection = mysql.createConnection(dbconfig);

function doExist(data, callback){
	connection.connect();
	connection.query('select * from testaccount where username=?',[data.username], function(err,rows){
		//if(err) throw err;
		console.log(rows);
		if(rows[0].username){
			callback(true);
		}else{
			callback(false);
		}
	});
	connection.end();
}

function register(data, callback){
	connection.connect();
	connection.query('insert into testaccount set ?', data, function(err, res){
		console.log(err);console.log(res);
	});
	connection.end();
}
doExist({username:'username'},function(err){
	if(!err){
		register({
			username:'username'
		},function(err){
			
		});
	}
});