What you're referring to is called "callback hell". The easiest way to get out of that is to use a Promise library that simplifies it.
I used a node package called bluebird
.
var mysql = require("mysql");
var hash = require("password-hash");
var Promise = require("bluebird");
var settings = require("../settings");
Promise.promisifyAll(require("mysql/lib/Connection").prototype);
Promise.promisifyAll(require("mysql/lib/Pool").prototype);
var db_config = {
user:settings.db.user,
password:settings.db.password,
database:settings.db.database
};
var con = mysql.createPool(db_config);
function query(sql) {
return con.getConnectionAsync().then(function(connection) {
return connection.queryAsync(sql)
.spread(function(rows,fields) {
return rows;
}).finally(function() {
connection.release();
});
});
}
This is a very basic database module I wrote that uses bluebird
to promisify
the database object.
And here's how it's used. It returns a promise! The benefit here is that not only does it return the clutter of callback hell, it makes sure that your code runs asynchronously and the function does not return before things have stopped processing, like in this case, a database query.
function login(user) {
//check for player existance
var query = 'SELECT p.name,p.password,p.id, pd.x, pd.y FROM player p INNER JOIN player_data pd ON p.id = pd.id WHERE p.name='+mysql.escape(user);
return db.select(query).then(function(rows) {
if (!rows.length) return;
return [
rows[0]
];
});
}
Notice how you return a promise, so that you call the then
or spread
method to get those database values you just queried, not having to worry about if rows
will be undefined by the time you want to use it.