NodeJS and ExpressJS parallel processing of rest request - node.js

Question

I am newbie with JavaScript, NodeJS and Express. I writing simple application which does the following
User makes a request.
Server makes mulitple rest calls and renders the response.
How can I make sure that all the calls are complete and I create an object that I can send to the user? I saw people said something about async.parallel. Is that the only way to go? Any examples would help.

Answer 1

You can use promises to run code in sequence.
Here is an example (a little scaled down) of a login functionality I made using promises.
In a module named LoginController I have placed this piece of code.
this.attemptLogin = function(body, res) {
var reason = "";
var user = null;
loginM.findUser(body.username)
.then(function(result) {
if (result.status) {
user = result.result[0];
return this.verifyPassword(body.password, result.result[0].Password);
} else {
reason = {status: false, message: "Incorrect username", result: null};
throw(reason);
}
})
.then(function(result) {
if (result.message) {
res.send({status: true, message: "Successfully logged in", result: user});
return;
} else {
reason = {status: false, message: "Incorrect password", result: null};
throw(reason);
}
}).catch(function(err) {
res.send(err);
});
}
And in another module named LoginModel (LoginM) I have placed this code
this.findUser = function(username, email) {
return new Promise(function (resolve, reject) {
pool.getConnection(function (err, connection) {
if (err) {
reject({status: false, message: err});
} else {
connection.query('select Id, Name, Email, Password from Users ' +
'where (Users.Name = ? OR Users.Email = ?) AND Removed = 0 LIMIT 1', [username, email], function (err, rows) {
connection.release();
if (!err) {
if(rows.length > 0) {
resolve({status: true, message: "Found user", result: rows});
}
else
resolve({status: false, message: null})
} else {
reject({status: false, message: err});
}
});
}
});
});
}
And a similar method for verifyPassword which also returns a promise.
Now, the things to note are that:
the code inside every then is run asynchronously
the then parts are executed in order, i.e, you won´t enter the next then until you have returned something from the previous then
whatever you resolve from the methods returning promises (findUser and verifyPassword) are passed as the variable named result in .then(function(result)