Ufdjrw

I'm new to Node and the concepts of promises, so I'm trying to wrap my head around the timing of when code will get called.

What I'm trying to do is to get a few different pieces of data from the database, then render it using pug.

If I had code like the following, when would the various bits of code get called, and would it achieve what I want it to achieve?

(apologies for any typos, this isn't compiled code)

function getData1(con) 
 return new Promise(function (resolve, reject) 
 con.query('Select * from Table1', function(err, result) 
 if (err) reject(err);
 else resolve(result);
 ) 
 )



function getData2(con) 
 return new Promise(function (resolve, reject) 
 con.query('Select * from Table2', function(err, result) 
 if (err) reject(err);
 else resolve(result);
 ) 
 )


app.get('/', (req, res) => {

 const mysql = require('mysql');
 const con = mysql.createConnection(blah blah blah
 );

con.connect((err) => 
 if (err) throw err;
 console.log('Connected!');
);

var data1;
var getData1 = getData1(con);
getData1.then(function(result) 
 data1 = result;
)

var data2;
var getData2 = getData2(con);
getData2.then(function(result) 
 data2 = result;
)

res.render('index', data1: data1,
 data2 : data2);

I guess, more specifically, what I'm asking is:

1) Does getData1.then() and getData2() block, or do they behave like an event handler that gets called when the promise resolves?

2) Following on from that, Is res.render() only going to be called when we have values for data1, and data2, or does it need to be in the then() function?

3) If it needs to be in the then functions, what's a nice way to handle this given that I have two promises to wait for?

4) All the examples I saw for using the mysql module don't seem to use promises. Since getting a connection is asynchronous(?), isn't it possible that I'm trying to use the connection before I actually have it?

5) I'm from a java background so trying to think of this in terms of threads. Let's say both promises were rejected and I wanted to render the page with both errors, how would I go about building a list of error messages to be rendered? Is this like threads where both promises could reject at once and an attempt to build a list of errors is not safe? How would you go about making it thread safe?

thanks in advance for your comments!!